View source for Methylene blue

{{Short description|Blue dye also used as a medication}}
{{Distinguish|methyl blue|new methylene blue|methyl violet}}
{{cs1 config|name-list-style=vanc|display-authors=6}}
{{Infobox drug
| verifiedrevid = 464380613
| image = Methylene blue-2d-skeletal.svg
| image_class = skin-invert-image
| caption = Molecular structure
| image2 = Reflections in a flask of Methylene Blue.jpg
| INN = Methylthioninium chloride
| caption2 = A volumetric flask of a methylene blue solution

<!--Clinical data-->| tradename = Urelene blue, Provayblue, Proveblue, others<ref name=Ric2015>{{cite book| vauthors = Hamilton R |title=Tarascon Pocket Pharmacopoeia 2015 Deluxe Lab-Coat Edition|date=2015|publisher=Jones & Bartlett Learning|isbn=978-1-284-05756-0|page=471}}</ref><ref name=BNF69/>
| Drugs.com = {{drugs.com|monograph|methylene-blue}}
| DailyMedID = Provayblue
| pregnancy_AU = D
| pregnancy_category = 
| routes_of_administration = [[By mouth]], [[Intravenous therapy|intravenous]]
| ATC_prefix = V03
| ATC_suffix = AB17
| ATC_supplemental = {{ATC|V04|CG05}}
| legal_AU = <!-- S2, S3, S4, S5, S6, S7, S8, S9 or Unscheduled-->
| legal_CA = <!-- Schedule I, II, III, IV, V, VI, VII, VIII -->
| legal_UK = <!-- GSL, P, POM, CD, or Class A, B, C -->
| legal_US = Rx-only
| legal_US_comment = <ref name="Provayblue FDA label">{{cite web | title=Provayblue- methylene blue injection | website=DailyMed | date=29 June 2022 | url=https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=4f6848e5-35ed-4046-b13c-3032b5ba3232 | access-date=4 March 2023}}</ref><ref name=AHFS2017/>
| legal_EU = Rx-only
| legal_EU_comment = <ref name="Lumeblue EPAR">{{cite web | title=Lumeblue EPAR | website=European Medicines Agency | date=19 June 2020 | url=https://www.ema.europa.eu/en/medicines/human/EPAR/lumeblue | access-date=4 March 2023}}</ref><ref>{{cite web | title=Lumeblue Product information | website=Union Register of medicinal products | url=https://ec.europa.eu/health/documents/community-register/html/h1470.htm | access-date=3 March 2023}}</ref>

<!--Pharmacokinetic data-->| bioavailability = 
| protein_bound = 
| metabolism = 
| elimination_half-life = 5–24 hours ({{abbrlink|IV|intravenous therapy}})<ref name=AHFS2017/>
| excretion = Renal<br />In rats: 18%({{abbrlink|PO|Oral administration}}), 28% ({{abbr|IV}})<ref name="pmid10952480">{{cite journal | vauthors = Peter C, Hongwan D, Küpfer A, Lauterburg BH | title = Pharmacokinetics and organ distribution of intravenous and oral methylene blue | journal = European Journal of Clinical Pharmacology | volume = 56 | issue = 3 | pages = 247–250 | date = June 2000 | pmid = 10952480 | doi = 10.1007/s002280000124 }}</ref><!--Identifiers-->
| CAS_number_Ref = {{cascite|correct|??}}
| CAS_number = 61-73-4
| ChEMBL_Ref = {{ebicite|correct|EBI}}
| ChEMBL = 405110
| PubChem = 6099
| DrugBank_Ref = {{drugbankcite|correct|drugbank}}
| DrugBank = DB09241
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 5874
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 8NAP7826UB
| KEGG = D10537
| KEGG2 = C00220
| ChEBI_Ref = {{ebicite|correct|EBI}}
| ChEBI = 6872
| synonyms = [[Colour Index International|CI]] 52015, basic blue 9<ref name="Lillie, 1977">{{cite book | vauthors = Lillie RD |title=H. J. Conn's Biological stains |date=1977 |publisher=Williams & Wilkins |location=Baltimore |pages=692p |edition=9th}}</ref>

<!--Chemical data-->| IUPAC_name = 3,7-bis(Dimethylamino)-phenothiazin-5-ium chloride
| chemical_formula = 
| C = 16
| H = 18
| Cl = 1
| N = 3
| S = 1
| SMILES = CN(C)c1ccc2c(c1)sc-3cc(=[N+](C)C)ccc3n2.[Cl-]
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/C16H18N3S.ClH/c1-18(2)11-5-7-13-15(9-11)20-16-10-12(19(3)4)6-8-14(16)17-13;/h5-10H,1-4H3;1H/q+1;/p-1
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = CXKWCBBOMKCUKX-UHFFFAOYSA-M
}}

<!-- Definition and uses -->
'''Methylthioninium chloride''', commonly called '''methylene blue''', is a [[Salt (chemistry)|salt]] used as a [[dye]] and as a medication. As a medication, it is mainly used to treat [[methemoglobinemia]]. It has previously been used for treating [[cyanide poisoning]] and [[urinary tract infection]]s, but this use is no longer recommended.<ref name=AHFS2017/>  It has also been used to treat cases of [[malaria]] for over a century.<ref>{{Cite web |last=MPH |first=Leslie Goldman |date=2025-04-24 |title=What to know about methylene blue |url=https://www.health.harvard.edu/diseases-and-conditions/what-to-know-about-methylene-blue |access-date=2025-10-16 |website=Harvard Health |language=en}}</ref>

<!-- Side effects and mechanism -->
Methylene blue is typically given by [[intravenous|injection into a vein]].<ref name=AHFS2017>{{cite web|title=Methylene Blue|url=https://www.drugs.com/monograph/methylene-blue.html|publisher=The American Society of Health-System Pharmacists|access-date=8 January 2017|url-status=live|archive-url=https://web.archive.org/web/20170510111253/https://www.drugs.com/monograph/methylene-blue.html|archive-date=10 May 2017}}</ref> Common side effects include [[headache]], [[nausea]], and [[vomiting]].

<!-- History and culture -->
Methylene blue was first prepared in 1876, by [[Heinrich Caro]].<ref name=Ah2008>{{cite book| vauthors = Ahmad I, Aqil F |title=New Strategies Combating Bacterial Infection |date=2008 |publisher=John Wiley & Sons |isbn=978-3-527-62294-8 |page=91 |url=https://books.google.com/books?id=Hrdzorisyp8C&pg=PA91 |language=en |url-status=live |archive-url=https://web.archive.org/web/20170918205927/https://books.google.com/books?id=Hrdzorisyp8C&pg=PA91|archive-date=2017-09-18}}</ref> It is on the [[WHO Model List of Essential Medicines|World Health Organization's List of Essential Medicines]].<ref name="WHO21st">{{cite book | vauthors = ((World Health Organization)) | title = World Health Organization model list of essential medicines: 21st list 2019 | year = 2019 | hdl = 10665/325771 | author-link = World Health Organization | publisher = World Health Organization | location = Geneva | id = WHO/MVP/EMP/IAU/2019.06. License: CC BY-NC-SA 3.0 IGO }}</ref>

==Medical uses==

===Methemoglobinemia===
Methylene blue is used to treat [[methemoglobinemia]] by [[redox|chemically reducing]] the [[ferric iron]] in [[hemoglobin]] to [[ferrous iron]].<ref name="AHFS2017" /><ref name="BNF69">{{cite book |title=British national formulary: BNF 69 |date=2015 |publisher=British Medical Association |isbn=978-0-85711-156-2 |edition=69 |page=34}}</ref> Methemoglobinemia can arise from ingestion of certain pharmaceuticals, [[toxin]]s, or [[Vicia faba|broad beans]] in those susceptible.<ref>{{cite book | vauthors = Thomé SD, Petz LD | chapter = Hemolytic Anemia: Hereditary and Acquired | veditors = Mazza J |title=Manual of Clinical Hematology |date=2002 |publisher=Lippincott Williams & Wilkins |location=Philadelphia |isbn=978-0-7817-2980-2 |page=102 |edition=3rd | chapter-url = https://books.google.com/books?id=NzMKMPzbxZwC&pg=PA102 }}</ref> Specifically, it is used to treat methemoglobin levels that are greater than 30% or in which there are symptoms despite [[oxygen therapy]].<ref name="BNF69" /> Normally, through the [[NADH]]- or [[NADPH]]-dependent [[methemoglobin reductase]] enzymes, methemoglobin is reduced back to hemoglobin. When large amounts of methemoglobin occur secondary to toxins, methemoglobin reductases are overwhelmed. Methylene blue, when injected intravenously as an antidote, is itself first reduced to leucomethylene blue, which then reduces the [[heme]] group from [[methemoglobin]] to [[hemoglobin]]. Methylene blue can reduce the half-life of methemoglobin from hours to minutes.<ref name="brent">
{{Cite book| vauthors = Brent J | title =Critical care toxicology: diagnosis and management of the critically poisoned patient.| publisher = [[Elsevier Health Sciences]]| year =2005 }}</ref> At high doses, however, methylene blue actually induces methemoglobinemia, reversing this pathway.<ref name="brent"/>

====Isobutyl nitrite toxicity====
[[Isobutyl nitrite]] is one of the compounds used as [[poppers]], an [[inhalant]] drug that induces a brief [[euphoria]].

Isobutyl nitrite is known to cause [[methemoglobinemia]].<ref>{{cite journal | vauthors = Taylor GM, Avera RS, Strachan CC, Briggs CM, Medler JP, Pafford CM, Gant TB | title = Severe methemoglobinemia secondary to isobutyl nitrite toxicity: the case of the 'Gold Rush' | journal = Oxford Medical Case Reports | volume = 2021 | issue = 2 | article-number = omaa136 | date = February 2021 | pmid = 33614047 | pmc = 7885148 | doi = 10.1093/omcr/omaa136 }}</ref> Severe methemoglobinemia may be treated with methylene blue.<ref>{{cite journal | vauthors = Modarai B, Kapadia YK, Kerins M, Terris J | title = Methylene blue: a treatment for severe methaemoglobinaemia secondary to misuse of amyl nitrite | journal = Emergency Medicine Journal | volume = 19 | issue = 3 | pages = 270–271 | date = May 2002 | pmid = 11971852 | pmc = 1725875 | doi = 10.1136/emj.19.3.270 }}</ref>

===In a combination drug: Methylphen===
{{excerpt|Hyoscyamine/hexamethylenetetramine/phenyl salicylate/methylene blue/benzoic acid|paragraphs=1}}

===Cyanide poisoning===
Since its reduction potential is similar to that of oxygen and can be reduced by components of the [[electron transport chain]], large doses of methylene blue are sometimes used as an antidote to [[potassium cyanide]] poisoning, a method first successfully tested in 1933 by [[Matilda Moldenhauer Brooks]] in San Francisco,<ref name = "brooks" /> although first demonstrated by Bo Sahlin of [[Lund University]], in 1926.<ref name = "brooks">{{Cite journal | title = Methylene blue as an antidote for cyanide and carbon monoxide poisoning | vauthors = Brooks MM | journal = The Scientific Monthly | volume = 43 | issue = 6 | year = 1936 | pages = 585–586| jstor =16280| bibcode = 1936SciMo..43..585M }}</ref><ref>{{cite journal | doi = 10.1001/jama.1933.02740050053028| title = Methylene Blue As Antidote for Cyanide Poisoning| journal = JAMA| volume = 100| issue = 5| page = 357| date = 4 February 1933| vauthors = Hanzlik PJ }}</ref>

===Shock===
Methylene blue increases blood pressure in people with [[vasoplegic syndrome]] (redistributive shock). It does not improve delivery of oxygen to tissues or decrease mortality.<ref>{{cite journal | vauthors = Hosseinian L, Weiner M, Levin MA, Fischer GW | title = Methylene Blue: Magic Bullet for Vasoplegia? | journal = Anesthesia and Analgesia | volume = 122 | issue = 1 | pages = 194–201 | date = January 2016 | pmid = 26678471 | doi = 10.1213/ANE.0000000000001045 | s2cid = 26114442 }}</ref><ref>{{cite journal | vauthors = Stawicki SP, Sims C, Sarani B, Grossman MD, Gracias VH | title = Methylene blue and vasoplegia: who, when, and how? | journal = Mini Reviews in Medicinal Chemistry | volume = 8 | issue = 5 | pages = 472–490 | date = May 2008 | pmid = 18473936 | doi = 10.2174/138955708784223477 | url = http://www.bentham-direct.org/pages/content.php?MRMC/2008/00000008/00000005/0006N.SGM | access-date = 2020-04-01 | url-status = usurped | archive-url = https://web.archive.org/web/20170918205928/http://www.bentham-direct.org/pages/content.php?MRMC%2F2008%2F00000008%2F00000005%2F0006N.SGM | archive-date = 2017-09-18 | url-access = subscription }}</ref>

Methylene blue has been used in [[calcium channel blocker]] toxicity as a possible rescue therapy for distributive shock unresponsive to first-line agents. Limited to [[case report]]s, a 2024 review found low-quality evidence that methylene blue may reduce short-term mortality, duration of the need for vasopressors, and length of hospital stay.<ref name="fern">{{cite journal | vauthors = Fernando SM, Tran A, Soliman K, Flynn B, Oommen T, Wenzhe L, Adhikari NK, Kanji S, Seely AJ, Fox-Robichaud AE, Wax RS, Cook DJ, Lamontagne F, Rochwerg B | title = Methylene Blue in Septic Shock: A Systematic Review and Meta-Analysis | journal = Critical Care Explorations | volume = 6 | issue = 7 | article-number = e1110 | date = July 2024 | pmid = 38904978 | pmc = 11196076 | doi = 10.1097/CCE.0000000000001110 }}</ref>

===Dye or stain===
[[File:Human Cheek Cells.jpg|thumb|280x280px|Human cheek cells stained with methylene blue]]
[[File:Methylene blue Crystals.jpg|thumb|Methylene blue crystals]]
Methylene blue is used in [[colonoscopy|endoscopic]] [[polyp (medicine)|polypectomy]] as an adjunct to [[Saline (medicine)|saline]] or [[epinephrine]], and is used for injection into the [[submucosa]] around the [[Polyp (medicine)|polyp]] to be removed. This allows the submucosal tissue plane to be identified after the polyp is removed, which is useful in determining if more tissue needs to be removed or if there is a high risk for perforation. Methylene blue is also used as a dye in [[endoscopy|chromoendoscopy]], and is sprayed onto the mucosa of the [[gastrointestinal tract]] to identify [[dysplasia]], or pre-cancerous lesions. Intravenously injected methylene blue is readily released into the urine.<ref name="lu-18">{{cite journal |vauthors=Lu G, Nagbanshi M, Goldau N, Mendes Jorge M, Meissner P, Jahn A, Mockenhaupt FP, Müller O |title=Efficacy and safety of methylene blue in the treatment of malaria: a systematic review |journal=BMC Medicine |volume=16 |issue=1 |article-number=59 |date=April 2018 |pmid=29690878 |pmc=5979000 |doi=10.1186/s12916-018-1045-3|doi-access=free}}</ref>

In surgeries such as [[sentinel lymph node]] dissections, methylene blue can be used to visually trace the lymphatic drainage of tested tissues. Similarly, methylene blue is added to [[bone cement]] in orthopedic operations to provide easy discrimination between native bone and cement. Additionally, methylene blue accelerates the hardening of bone cement, increasing the speed at which bone cement can be effectively applied. Methylene blue is used as an aid to visualisation/orientation in several medical devices, including a [[surgical sealant film]]. It can also be used during gastrointestinal surgeries (such as [[bowel resection]] or [[gastric bypass surgery|gastric bypass]]) to test for leaks.{{Citation needed|date=January 2021}}

It is sometimes used in [[cytopathology]], in mixtures including [[Wright-Giemsa]] and [[Diff-Quik]]. It confers a blue color to both nuclei and cytoplasm, and makes the nuclei more visible.<ref name="pmid26664363">{{cite journal | vauthors = Hu X, Laguerre V, Packert D, Nakasone A, Moscinski L | title = A Simple and Efficient Method for Preparing Cell Slides and Staining without Using Cytocentrifuge and Cytoclips | journal = International Journal of Cell Biology | volume = 2015 | issue =  | article-number = 813216 | year = 2015 | pmid = 26664363 | pmc = 4664808 | doi = 10.1155/2015/813216 | doi-access = free }}</ref> When methylene blue is "polychromed" (oxidized in solution or "ripened" by fungal metabolism,<ref>{{Cite book | vauthors = Kiernan JA | chapter = Chapter 19: On Chemical Reactions and Staining Mechanisms   | series = Education Guide | veditors = Kumar GL, Kiernan JA | title = Special Stains and H & E | date = 2010 | edition = Second | location = Carpinteria, California | publisher = Dako North America, Inc.  |chapter-url= http://www.dako.com/08066_12may10_webchapter19.pdf |archive-url= https://web.archive.org/web/20120513002342/http://www.dako.com/08066_12may10_webchapter19.pdf | quote = What is Giemsa's stain and how does it color blood cells, bacteria and chromosomes? | page = 172 |archive-date=May 13, 2012}}</ref> as originally noted in the thesis of Dr. [[Romanowsky stain|D. L. Romanowsky]] in the 1890s), it gets serially demethylated and forms all the tri-, di-, mono- and non-methyl intermediates, which are [[Azure B]], [[Azure A]], [[Azure C]], and [[thionine]], respectively.<ref>{{cite journal | vauthors = Wilson TM | title = On the Chemistry and Staining Properties of Certain Derivatives of the Methylene Blue Group When Combined With Eosin | journal = The Journal of Experimental Medicine | volume = 9 | issue = 6 | pages = 645–670 | date = November 1907 | pmid = 19867116 | pmc = 2124692 | doi = 10.1084/jem.9.6.645 }}</ref> This is the basis of the basophilic part of the spectrum of [[Romanowsky stain|Romanowski-Giemsa]] effect. If only synthetic Azure B and [[Eosin Y]] is used, it may serve as a standardized [[Giemsa stain]]; but, without methylene blue, the normal neutrophilic granules tend to overstain and look like toxic granules. On the other hand, if methylene blue is used it might help to give the normal look of neutrophil granules and may also enhance the staining of nucleoli and polychromatophilic RBCs (reticulocytes).<ref>{{cite book | vauthors = Lewis SM, Bain BK, Bates I, Dacie JV |title=Dacie and Lewis practical haematology |date=2006 |publisher=Churchill Livingstone/Elsevier |location=Philadelphia, PA |isbn=978-0-443-06660-3 |edition=10th | page = 61 }}</ref>

[[File:Gross pathology of normal brain and brain of patient treated with methylene blue before death.jpg|thumb|Gross pathology of a normal brain and a brain of a patient treated with methylene blue before death.]]
A traditional application of methylene blue is the intravital or supravital staining of nerve fibers, an effect first described by [[Paul Ehrlich]] in 1887.<ref>{{cite journal | vauthors = Ehrlich P | date = 1887 | title = Ueber die Methylenblau Reaktion der lebenden Nerven Substanz. | trans-title = About the methylene blue reaction of the living nerve substance. | language = German | journal =Biologisches Zentralblatt | trans-journal = Biological Central Journal | volume = 6 | pages = 214–224 | url = https://www.pei.de/SharedDocs/Downloads/DE/institut/veroeffentlichungen-von-paul-ehrlich/1886-1896/1887-ueber-methylenblaureaktion-lebender-nervensubstanz.pdf?__blob=publicationFile&v=2 }} cited by {{cite book | vauthors = Baker JR | title = Principles of biological microtechnique. A study of fixation and dyeing. | date = 1958 | location = London | publisher = Methuen }}</ref> A dilute solution of the dye is either injected into tissue or applied to small freshly removed pieces. The selective blue coloration develops with exposure to air (oxygen) and can be fixed by immersion of the stained specimen in an aqueous solution of [[ammonium molybdate]]. Vital methylene blue was formerly much used for examining the innervation of muscle, skin, and internal organs.<ref>{{cite journal | vauthors = Wilson JG | title = Intra vitam staining with methylene blue. | journal = The Anatomical Record | date = July 1910 | volume = 4 | issue = 7 | pages = 267–277 | doi = 10.1002/ar.1090040705 | s2cid = 86242668 | url = https://zenodo.org/record/2478243 }}</ref><ref>{{cite journal | vauthors = Schabadasch A | title = Untersuchungen zur Methodik der Methylenblaufärbung des vegetativen Nervensystems. | trans-title = Investigations on the methodology of methylene blue staining of the autonomic nervous system. | language = German | journal = Zeitschrift für Zellforschung und Mikroskopische Anatomie | trans-journal = Journal of Cell Research and Microscopic Anatomy | date = January 1930 | volume = 10 | issue = 2 | pages = 221–243 | doi = 10.1007/BF02450696 | s2cid = 36940327 }}</ref><ref>{{cite book | vauthors = Zacks SI | date = 1973 | title = The Motor Endplate | edition = 2nd | location = Huntington, NY | publisher = Krieger }}</ref> The mechanism of selective dye uptake is incompletely understood; vital staining of nerve fibers in skin is prevented by [[ouabain]], a drug that inhibits the Na/K-ATPase of cell membranes.<ref name="Kiernan_1974">{{cite journal | vauthors = Kiernan JA | title = Effects of metabolic inhibitors on vital staining with methylene blue | journal = Histochemistry | volume = 40 | issue = 1 | pages = 51–57 | date = June 1974 | pmid = 4136702 | doi = 10.1007/BF00490273 | s2cid = 23158612 }}</ref>

===Placebo===
Methylene blue has been used as a [[placebo]]; physicians would tell their patients to expect their urine to change color and view this as a sign that their condition had improved.<ref>{{Cite web| url =http://www.sciencebasedmedicine.org/?p=29| title =The ethics of deception in medicine| access-date =2008-01-24| vauthors = Novella S | work =Science Based Medicine| date =23 January 2008| url-status =live| archive-url =https://web.archive.org/web/20080129230034/http://www.sciencebasedmedicine.org/?p=29| archive-date =2008-01-29}}</ref> This same side effect makes methylene blue difficult to use in traditional placebo-controlled [[clinical studies]], including those testing for its efficacy as a treatment. One approach is to use a low dose, just enough to turn urine blue, as the placebo group.<ref>{{ClinicalTrialsGov|NCT00214877|Methylene blue for cognitive dysfunction in bipolar disorder}}</ref> However, a low dose does not guarantee inertness.<ref name=psych/>

==Side effects==
{| class="wikitable"
! Cardiovascular<ref name="Mokhlesi2003">{{cite journal | vauthors = Mokhlesi B, Leikin JB, Murray P, Corbridge TC | title = Adult toxicology in critical care: Part II: specific poisonings | journal = Chest | volume = 123 | issue = 3 | pages = 897–922 | date = March 2003 | pmid = 12628894 | doi = 10.1378/chest.123.3.897 | s2cid = 9962335 }}</ref><ref name="Harvey1983">{{cite journal | vauthors = Harvey JW, Keitt AS | title = Studies of the efficacy and potential hazards of methylene blue therapy in aniline-induced methaemoglobinaemia | journal = British Journal of Haematology | volume = 54 | issue = 1 | pages = 29–41 | date = May 1983 | pmid = 6849836 | doi = 10.1111/j.1365-2141.1983.tb02064.x | s2cid = 19304915 }}</ref>
! Central nervous system<ref name="Mokhlesi2003" /><ref name="Harvey1983" />
! Dermatologic<ref name="Mokhlesi2003" /><ref name="Harvey1983" />
! Gastrointestinal<ref name="Mokhlesi2003" /><ref name="Harvey1983" />
! Genito-urinary<ref name="Mokhlesi2003" /><ref name="Harvey1983" />
! Hematologic<ref name="Mokhlesi2003" /><ref name="Harvey1983" />
|- style="vertical-align:top"
|
* [[Hypertension]]
* [[Precordial]] [[pain]]
|
* [[Dizziness]]
* Mental confusion
* [[Headache]]
* [[Fever]]
|
* Staining of skin
* Injection site [[necrosis]] (SC)
|
* Fecal discoloration
* [[Nausea]]
* [[Vomiting]]
* [[Abdominal]] [[pain]]
|
* Discoloration of [[urine]] (doses over 80&nbsp;μg)
* [[Bladder]] irritation
|
* [[Anemia]]
|}

Methylene blue is a [[monoamine oxidase inhibitor]] (MAOI)<ref>
{{cite journal | vauthors = Ramsay RR, Dunford C, Gillman PK | title = Methylene blue and serotonin toxicity: inhibition of monoamine oxidase A (MAO A) confirms a theoretical prediction | journal = British Journal of Pharmacology | volume = 152 | issue = 6 | pages = 946–951 | date = November 2007 | pmid = 17721552 | pmc = 2078225 | doi = 10.1038/sj.bjp.0707430 }}</ref> and, if infused intravenously at doses exceeding 5&nbsp;mg/kg, may result in [[serotonin syndrome]] if combined with any [[selective serotonin reuptake inhibitor]]s (SSRIs) or other serotonergic drugs (e.g., [[duloxetine]], [[sibutramine]], [[venlafaxine]], [[clomipramine]], [[imipramine]]).<ref name="pmid16978328">{{cite journal | vauthors = Gillman PK | title = Methylene blue implicated in potentially fatal serotonin toxicity | journal = Anaesthesia | volume = 61 | issue = 10 | pages = 1013–1014 | date = October 2006 | pmid = 16978328 | doi = 10.1111/j.1365-2044.2006.04808.x | s2cid = 45063314 | doi-access =  }}</ref>

It causes [[hemolytic anemia]] in carriers of the [[G6PD]] enzymatic deficiency ([[favism]]).<ref>{{cite journal | vauthors = Rosen PJ, Johnson C, McGehee WG, Beutler E | title = Failure of methylene blue treatment in toxic methemoglobinemia. Association with glucose-6-phosphate dehydrogenase deficiency | journal = Annals of Internal Medicine | volume = 75 | issue = 1 | pages = 83–86 | date = July 1971 | pmid = 5091568 | doi = 10.7326/0003-4819-75-1-83 }}</ref> The actual degree of this danger is a subject of controversy as the association was made based on very few cases. A 2018 meta-analysis on clinical trials against malaria in Africa, where the moderate A minus type of G6PD deficiency is prevalent, shows no association between MB and hemolysis in such patients. There was, however, a clinically insignificant reduction in hemoglobin.<ref name=Lu2018/>

== Pregnancy ==
While use during [[pregnancy]] may harm the baby, not using it in methemoglobinemia is likely more dangerous.<ref name="AHFS2017" /><ref name="BNF69" />

== Pharmacokinetics ==
After intravenous administration in humans, methylene blue shows a multiphasic change in concentration, with a terminal half-life of 5.25 hours. The initial disappearance from blood actually reflects its movement into organs, with brain, liver, and bile all showing significantly higher concentrations than blood in rats. The overall [[Area under the curve (pharmacokinetics)|area under the curve]] in oral (dry gelatin capsule) administration is only 6.5% of the AUC for IV administration; judging from rat studies, the significantly altered organ distribution plays a key role in this difference.<ref name="pmid10952480"/>

Administration as an oral solution (500&nbsp;mg in 200&nbsp;mL) greatly increases the bioavailability to 72.3±23.9%. In this newer study, the terminal half-lives were reported as 18.5±11.8 hours for IV use and 18.3±7.2 hours for oral use. The t<sub>max</sub> for oral use is 2.2 hours, compared to 0.5 hours for iv use.<ref name="pmid18810398">{{cite journal | vauthors = Walter-Sack I, Rengelshausen J, Oberwittler H, Burhenne J, Mueller O, Meissner P, Mikus G | title = High absolute bioavailability of methylene blue given as an aqueous oral formulation | journal = European Journal of Clinical Pharmacology | volume = 65 | issue = 2 | pages = 179–189 | date = February 2009 | pmid = 18810398 | doi = 10.1007/s00228-008-0563-x | url = https://hal.archives-ouvertes.fr/hal-00477926/file/PEER_stage2_10.1007%252Fs00228-008-0563-x.pdf }}</ref>

==Chemistry==
Methylene blue is a formal derivative of [[phenothiazine]]. It is a dark green powder that yields a blue solution in [[water (molecule)|water]]. The hydrated form has 3 molecules of water per unit of methylene blue.

===Preparation===
This compound is prepared by oxidation of 4-aminodimethylaniline in the presence of [[sodium thiosulfate]] to give the quinonediiminothiosulfonic acid, reaction with dimethylaniline, oxidation to the indamine, and cyclization to give the thiazine:<ref name=ull>{{cite encyclopedia| vauthors = Berneth H |chapter=Azine Dyes |encyclopedia= Ullmann's Encyclopedia of Industrial Chemistry |year=2012 |publisher=Wiley-VCH |place=Weinheim |doi=10.1002/14356007.a03_213.pub3|isbn=978-3-527-30673-2}}</ref>
:[[File:Synthesis of methylene blue.png|class=skin-invert-image|600px]]
A green electrochemical procedure, using only [[dimethyl-4-phenylenediamine]] and sulfide ions has been proposed.<ref>{{Cite journal | vauthors = Maleki A, Nematollahi D |date=December 2009 |title=An efficient electrochemical method for the synthesis of methylene blue |url=https://linkinghub.elsevier.com/retrieve/pii/S1388248109004846 |journal=Electrochemistry Communications |language=en |volume=11 |issue=12 |pages=2261–2264 |doi=10.1016/j.elecom.2009.09.040|url-access=subscription }}</ref>

===Light absorption properties===
[[File:Methylene blue absorption spectrum.png|thumb|Absorption spectrum of methylene blue, in terms of the [[molar extinction coefficient]] (base 10 logarithm). In this dataset, a peak [[absorbance]] of 1.7 (i.e., 98% of transmitted light absorbed) was observed with 665 nm light passing through 1 cm of 10 micromolar methylene blue solution.]]
The maximum absorption of light is near 670&nbsp;nm. The specifics of absorption depend on several factors, including [[protonation]], [[adsorption]] to other materials, and [[metachromasy]] – the formation of [[Dimer (chemistry)|dimers]] and higher-order aggregates depending on concentration and other interactions:<ref>{{cite journal|title=Visible spectroscopy of methylene blue on hectorite, laponite B, and barasym in aqueous suspension| vauthors = Cenens J, Schoonheydt RA |journal=Clays and Clay Minerals |volume=36 |number=3 |pages=214–224 |year=1988 |doi=10.1346/ccmn.1988.0360302 |bibcode=1988CCM....36..214C | s2cid = 3851037 |doi-access=}}</ref>

{| class="wikitable"
!Species
!Absorption peak
!Extinction coefficient (dm<sup>3</sup>/mol·cm)
|-
| MB<sup>+</sup> (solution)
| 664
| 95000
|-
| MBH<sub>2</sub><sup>+</sup> (solution)
| 741
| 76000
|-
| (MB<sup>+</sup>)<sub>2</sub> (solution)
| 605
| 132000
|-
| (MB<sup>+</sup>)<sub>3</sub> (solution)
| 580
| 110000
|-
| MB<sup>+</sup> (adsorbed on clay)
| 673
| 116000
|-
| MBH<sub>2</sub><sup>+</sup> (adsorbed on clay)
| 763
| 86000
|-
| (MB<sup>+</sup>)<sub>2</sub> (adsorbed on clay)
| 596
| 80000
|-
| (MB<sup>+</sup>)<sub>3</sub> (adsorbed on clay)
| 570
| 114000
|}

=== Redox properties ===
[[File:Methylene Blue Redox Reaction.svg|thumb|right|Reversible reduction of methylene blue]]
Under reducing conditions, the blue-colored methylene blue cation (MB<sup>+</sup>) gains 1H<sup>+</sup> and 2e<sup>−</sup> to become the electrically neutral and colorless '''leucomethylene blue''' (LMB).<ref>{{cite book |chapter=Methylene Blue | chapter-url = https://publications.iarc.fr/_publications/media/download/6707/581359b111699ead293649c15000080016dce9f3.pdf |title=IARC Monographs on the Evaluation of Carcinogenic Risks to Humans  |pages= 155–183 (166) |volume=108|date=2016}}</ref> The redox midpoint potential E{{sub|0}}' is +0.01 V.<ref>{{cite book | vauthors = Jakubowski H | date = 2016 | chapter = Chapter 8: Oxidation/Phosphorylation B: Oxidative Enzymes | title = Biochemistry Online | chapter-url = https://employees.csbsju.edu/hjakubowski/classes/ch331/oxphos/oloxidativeenzymes.html }}</ref>

The redox properties can be seen in a classical demonstration of [[chemical kinetics]] in general chemistry, the "[[Blue bottle (chemical reaction)|blue bottle]]" experiment. Typically, a solution is made of [[glucose]] (dextrose), methylene blue, and [[sodium hydroxide]]. Upon shaking the bottle, [[oxygen]] oxidizes methylene blue, and the solution turns blue. The dextrose will gradually reduce the methylene blue to its colorless, reduced form. Hence, when the dissolved dextrose is entirely consumed, the solution will turn blue again.<ref name="Cook1994"/>

In the [[Mitochondrion|mitochondrial]] [[electron transport chain]], reduced methylene blue (MBH<sub>2</sub>) directly reduces [[cytochrome c]] rather than to oxygen, limiting the formation of [[superoxide]].<ref name="pmid17928358">{{cite journal | vauthors = Atamna H, Nguyen A, Ames BN | title = Methylene blue delays cellular senescence and enhances key mitochondrial biochemical pathways | journal = [[The FASEB Journal]] | volume = 22 | issue=3 | pages = 703–712 | date = 2008 |url=https://d1wqtxts1xzle7.cloudfront.net/41715377/fj.07-9610com.full-libre.pdf?1454057116=&response-content-disposition=inline%3B+filename%3DMethylene_blue_delays_cellular_senescenc.pdf&Expires=1743199680&Signature=ItIIdTkGebvWdx5Xp7QM4EAb1FWD6ytz5jmUrmR6r25dQwDj53ZGRMgXjUvkX7xhMJCwYSS8LNqQ0TT5oiLJWgvdQyEAiyMoTkdCLInanRGNP6xW5GhYlLWfwIwILUbKZyKOMF-fjc-PTTtjvZNgyiR3yJIhxLBOfooWCg9i10w4-6qZu5oTulqcwUQmBbSBzdtETJBxRemlydYjJDSMqnpzOUPDfdJsF1OhJJ0kTbWJ3nh18RQvH68~9InEZsCMgP5EYTd64K5dF~ss-uYwnDoDTTDIdr48nWxYo1hfprrS9aLymKlk6OpPW1IZ9Pk4oDS4xg1TPCQ4zK7InhD0RQ__&Key-Pair-Id=APKAJLOHF5GGSLRBV4ZA | doi = 10.1096/fj.07-9610com  | doi-access = free | pmid = 17928358 }}</ref><ref name="pmid23118969">{{cite journal | vauthors = Poteet E, Winters A, Yang S | title = Neuroprotective actions of methylene blue and its derivatives | journal = [[PLOS One]] | volume = 7 | issue = 10 | article-number = e48279 | date = 2012 | doi = 10.1371/journal.pone.0048279 | doi-access = free | pmc = 3485214 | pmid = 23118969 | bibcode = 2012PLoSO...748279P }}</ref> 
Methylene blue has been shown to directly accept electrons from [[Nicotinamide adenine dinucleotide|NADH]], [[Nicotinamide adenine dinucleotide phosphate|NADPH]], and [[Flavin adenine dinucleotide|FADH<sub>2</sub>]].<ref name="pmid23118969" />

==Other uses==

===Redox indicator===
Methylene blue is widely used as a [[redox indicator]] in [[analytical chemistry]].<ref name="Cook1994">{{cite journal | vauthors = Cook AG, Tolliver RM, Williams JE |title=The Blue Bottle experiment revisited: How Blue? How Sweet? |journal=Journal of Chemical Education |date=February 1994 |volume=71 |issue=2 |page=160 |doi=10.1021/ed071p160|bibcode=1994JChEd..71..160C }}</ref><ref name="Anderson2012">{{cite journal | vauthors = Anderson L, Wittkopp SM, Painter CJ, Liegel JJ, Schreiner R, Bell JA, Shakhashiri BZ |title=What is happening when the Blue Bottle bleaches: An Investigation of the methylene blue-catalyzed air oxidation of glucose |journal=Journal of Chemical Education |date=9 October 2012 |volume=89 |issue=11 |pages=1425–1431 |doi=10.1021/ed200511d|bibcode=2012JChEd..89.1425A }}</ref><ref name="Rajchakit2016">{{cite journal | vauthors = Rajchakit U, Limpanuparb T |title=Rapid Blue Bottle experiment: Autoxidation of benzoin catalyzed by redox indicators |journal=Journal of Chemical Education |date=9 August 2016 |volume=93 |issue=8 |pages=1490–1494 |doi=10.1021/acs.jchemed.6b00018|bibcode=2016JChEd..93.1490R }}</ref> Solutions of this substance are blue when in an oxidizing environment, but will turn colorless if exposed to a reducing agent.<ref name="Harvey1919">{{cite journal | vauthors = Harvey EN | title = The relation between the oxygen concentration and rate of reduction of methylene blue by milk | journal = The Journal of General Physiology | volume = 1 | issue = 4 | pages = 415–419 | date = March 1919 | pmid = 19871757 | pmc = 2140316 | doi = 10.1085/jgp.1.4.415 }}</ref><ref name="Anderson2012" />

===Photosensitizer===
Methylene blue is also a [[photosensitizer]] used to create [[singlet oxygen]] when exposed to both oxygen and light. It is used in this regard to make organic [[peroxides]] by a [[Diels-Alder]] reaction which is [[selection rule#Electronic spectra|spin forbidden]] with normal atmospheric [[triplet oxygen]].{{Citation needed|date=January 2021}}

With the help of light, methylene blue can be used to kill some viruses and some bacteria.<ref name=asm>{{cite web |title=Methylene Blue: The Little-Known Disinfectant |url=https://asm.org/articles/2022/march/methylene-blue-the-little-known-disinfectant |website=ASM.org |language=en}}</ref> This kind of photo-disinfection has also been done inside of human bodies ([[antimicrobial photodynamic therapy]]).<ref>{{cite journal | vauthors = Boltes Cecatto R, Siqueira de Magalhães L, Fernanda Setúbal Destro Rodrigues M, Pavani C, Lino-Dos-Santos-Franco A, Teixeira Gomes M, Fátima Teixeira Silva D | title = Methylene blue mediated antimicrobial photodynamic therapy in clinical human studies: The state of the art | journal = Photodiagnosis and Photodynamic Therapy | volume = 31 | article-number = 101828 | date = September 2020 | pmid = 32473398 | doi = 10.1016/j.pdpdt.2020.101828 }}</ref> The same process can also be used to disinfect blood plasma.<ref>{{cite journal | vauthors = Lachert E |title=Methods of pathogen inactivation in whole blood and red blood cells: current state of knowledge |journal=Acta Haematologica Polonica |date=31 August 2021 |volume=52 |issue=4 |pages=406–411 |doi=10.5603/AHP.2021.0076 |url=https://journals.viamedica.pl/acta_haematologica_polonica/article/download/AHP.2021.0076/63958|doi-access=free }}</ref>

Methylene blue is theoretically also applicable to other forms of [[photodynamic therapy]], i.e., the use of oxygen, light, and a photosensitizer to kill cells. Research on using it to kill cancer cells locally is in a preclinical stage.<ref>{{cite journal | vauthors = Taldaev A, Terekhov R, Nikitin I, Melnik E, Kuzina V, Klochko M, Reshetov I, Shiryaev A, Loschenov V, Ramenskaya G | title = Methylene blue in anticancer photodynamic therapy: systematic review of preclinical studies | journal = Frontiers in Pharmacology | volume = 14 | article-number = 1264961 | date = 28 September 2023 | pmid = 37841915 | pmc = 10568458 | doi = 10.3389/fphar.2023.1264961 | doi-access = free }}</ref> Its cytotoxicity may be related to its ability to inhibit [[tubulin]] polymerization.<ref>{{Cite journal | vauthors = Baksheeva VE, La Rocca R, Allegro D, Derviaux C, Pasquier E, Roche P, Morelli X, Devred F, Golovin AV, Tsvetkov PO | title = NanoDSF Screening for Anti-tubulin Agents Uncovers New Structure–Activity Insights | journal = Journal of Medicinal Chemistry | date = 2025 | doi = 10.1021/acs.jmedchem.5c01008 }}</ref>

===Sulfide analysis===
The formation of methylene blue after the reaction of [[hydrogen sulfide]] with [[dimethyl-p-phenylenediamine]] and [[Ferric|iron(III)]] at pH&nbsp;0.4&nbsp;–&nbsp;0.7 is used to determine by [[Ultraviolet-visible spectroscopy|photometric measurements]] [[sulfide]] concentration in the range 0.020 to 1.50&nbsp;mg/L (20&nbsp;ppb to 1.5&nbsp;ppm).<ref name="Siegel1965">{{cite journal | vauthors = Siegel LM | title = A direct microdetermination for sulfide | journal = Analytical Biochemistry | volume = 11 | issue = 1 | pages = 126–132 | date = April 1965 | pmid = 14328633 | doi = 10.1016/0003-2697(65)90051-5 }}</ref> The test is very sensitive and the blue coloration developing upon contact of the reagents with dissolved H<sub>2</sub>S is stable for 60&nbsp;min. Ready-to-use kits such as the ''Spectroquant'' [[sulfide]] test<ref>{{cite web|url=http://photometry.merck.de/|title=Analytik und Probenvorbereitung|archive-url=https://web.archive.org/web/20070315204844/http://photometry.merck.de/|archive-date=2007-03-15 | publisher = Merck KGaA | location = Darmstadt, Germany }}</ref> facilitate routine analyses. The methylene blue sulfide test is a convenient method often used in soil microbiology to quickly detect in water the metabolic activity of [[sulfate reducing bacteria]] (SRB). In this colorimetric test, methylene blue is a product formed by the reaction and not a reagent added to the system.<ref name="Siegel1965" />

The addition of a strong [[reducing agent]], such as [[ascorbic acid]], to a sulfide-containing solution is sometimes used to prevent sulfide oxidation from atmospheric oxygen. Although it is certainly a sound precaution for the determination of sulfide with an [[ion selective electrode]], it might however hamper the development of the blue color if the freshly formed methylene blue is also reduced, as described here above in the paragraph on redox indicator.<ref name="Anderson2012" />

===Test for milk freshness===
Methylene blue is a dye behaving as a [[redox indicator]] that is commonly used in the [[food industry]] to test the freshness of [[milk]] and [[dairy]] products.<ref name=AHFS2017/><ref name = "Thornton_1930">{{cite journal | vauthors = Thornton H |title=Studies on Oxidation-Reduction in Milk: The Methylene Blue Reduction Test |journal=Journal of Dairy Science |date=May 1930 |volume=13 |issue=3 |pages=221–245 |publisher=Elsevier Inc. |doi=10.3168/jds.S0022-0302(30)93520-5 |doi-access=free }}</ref> A few drops of methylene blue solution added to a sample of milk should remain blue (oxidized form in the presence of enough dissolved {{O2}}), otherwise (discoloration caused by the reduction of methylene blue into its colorless reduced form) the dissolved {{O2}} concentration in the milk sample is low indicating that the milk is not fresh (already abiotically oxidized by {{O2}} whose concentration in solution decreases) or could be contaminated by [[bacteria]] also consuming the atmospheric {{O2}} dissolved in the milk.<ref name = "Thornton_1930" /> In other words, [[Oxygenation (environmental)|aerobic]] conditions should prevail in fresh milk, and methylene blue is simply used as an indicator of the dissolved oxygen remaining in the milk.<ref name="Harvey1919" />

===Water testing===
{{Further|MBAS assay}}

The adsorption of methylene blue serves as an indicator defining the adsorptive capacity of granular [[activated carbon]] in water filters. Adsorption of methylene blue is very similar to adsorption of pesticides from water; this quality makes methylene blue serve as a good predictor for filtration qualities of carbon. It is also a quick method of comparing different batches of activated carbon of the same quality.
A [[color reaction]] in an acidified, aqueous methylene blue solution containing [[chloroform]] can detect [[anionic surfactant]]s in a water sample. Such a test is known as an [[MBAS assay]] (methylene blue active substances assay).

The MBAS assay cannot distinguish between specific surfactants, however. Some examples of anionic surfactants are [[carboxylate]]s, [[phosphate]]s, [[sulfate]]s, and [[sulfonate]]s.{{citation needed|date=July 2022}}

===Methylene blue value of fine aggregate===
The methylene blue value is defined as the number of milliliters of standard methylene blue solution decolorized 0.1&nbsp;g of [[activated carbon]] (dry basis).<ref>{{cite web | title = Test Methods for Activated Carbon | url = https://activatedcarbon.org/images/Test_method_for_Activated_Carbon_86.pdf | work = European Council of Chemical Manufacturers' Federations | date = April 1986 }}</ref>
Methylene blue value reflects the amount of clay minerals in [[construction aggregate|aggregate]] samples.<ref>{{cite report |url=http://www.astm.org/Standards/C1777.htm| id = ASTM C1777 | title = Standard Test Method for Rapid Determination of the Methylene Blue Value for Fine Aggregate or Mineral Filler Using a Colorimeter | date = 7 July 2020 | location = West Conshohocken, PA | publisher = ASTM (American Society for Testing and Material) International |url-status=live |archive-url= https://web.archive.org/web/20140228153812/http://www.astm.org/Standards/C1777.htm |archive-date=2014-02-28 | doi = 10.1520/C1777-20 | url-access = subscription }}</ref> In  [[materials science]], methylene blue solution is successively added to fine aggregate which is being agitated in water. The presence of free dye solution can be checked with a stain test on a filter paper.<ref>{{Cite web | author = Standing Committee on Concrete Technology (SCCT) |url= https://www.cedd.gov.hk/filemanager/eng/content_78/cs3_2013_original.pdf |title=Construction Standard CS3:2013 – Aggregates for Concrete| publisher = The Government of the Hong Kong Special Administrative Region | date = May 2013 }}</ref>

===Biological staining===
{{cleanup section|reason=Duplicate of preceding stain section, just broader and "less medical".|date=February 2025}}
In biology, methylene blue is used as a [[dye]] for a number of different staining procedures, such as [[Wright's stain]] and [[Jenner's stain]]. Since it is a temporary staining technique, methylene blue can also be used to examine [[RNA]] or [[DNA]] under the [[microscope]] or in a gel: as an example, a solution of methylene blue can be used to stain RNA on hybridization membranes in [[northern blot]]ting to verify the amount of nucleic acid present. While methylene blue is not as sensitive as [[ethidium bromide]], it is less toxic and it does not [[Intercalation (biochemistry)|intercalate]] in nucleic acid chains, thus avoiding interference with nucleic acid retention on hybridization membranes or with the hybridization process itself.{{Citation needed|date=January 2021}}

It can also be used as an indicator to determine whether eukaryotic cells, such as yeast, are alive or dead. The methylene blue is reduced in viable cells, leaving them unstained. However, dead cells are unable to reduce the oxidized methylene blue, and the cells are stained blue. Methylene blue can interfere with the respiration of the yeast as it picks up hydrogen ions made during the process.{{Citation needed|date=January 2021}}

===Aquaculture===
* Methylene blue is used in [[aquaculture]] and by tropical fish hobbyists as a treatment for fungal infections.<ref name=fish/> With the help of light, it is also effective against bacteria and viruses.
* It can also be effective in treating fish infected with the parasitic [[protozoa]] ''[[Ichthyophthirius multifiliis]]'' (ich), although a combination of [[malachite green]] and [[formaldehyde]] is far more effective against it.<ref name=fish/>
* Methylene blue also works against nitrite poisoning as it treats the resulting methemoglobinemia. Like in humans, it also treats cyanide poisoning.
* Non-professional sources also claim that it works for ammonia poisoning,<ref>{{cite web |title=Methylene Blue as an Anti-Fungal & Anti-Parasitic Drug for Aquarium Fish |url=https://www.thesprucepets.com/methylene-blue-1379926 |website=The Spruce Pets |language=en}}</ref> but there is little medical literature to back this up.

It is usually used to protect newly laid fish eggs from being infected by fungus. This is useful when the hobbyist wants to artificially hatch the fish eggs.<ref name=fish>{{Cite web | title = Methylene Blue |url=https://www.3lfish.com/fish-medicants/#methylene-blue | work = 3 Little Fish Sdn Bhd |date=10 September 2021 | location = Kelana Jaya, Selangor, Malaysia }}</ref> For poisoning, injury (prevention of infection), or sickness, methylene blue is given as a "medicated bath" for the fish.

Methylene blue is not without side effects to fish.<ref>{{cite journal | vauthors = Nipu N, Wei L, Hamilton L, Lee H, Thomas J, Mennigen JA | title = Methylene blue at recommended concentrations alters metabolism in early zebrafish development | journal = Communications Biology | volume = 8 | issue = 1 | article-number = 120 | date = January 2025 | pmid = 39856203 | pmc = 11760885 | doi = 10.1038/s42003-025-07471-8 }}</ref>

==History==
Methylene blue has been described as "the first fully synthetic drug used in medicine". Methylene blue was first prepared in 1876 by German chemist [[Heinrich Caro]].<ref>Heinrich Caro was an employee of the Badische Anilin- und Sodafabrik, BASF, of Mannheim, Germany, which received a patent for methylene blue in 1877:
*  Badische Anilin- und Sodafabrik, BASF, of Mannheim, Germany, "Verfahren zur Darstellung blauer Farbstoffe aus Dimethylanilin und anderen tertiaren aromatischen Monaminen" [Method for preparation of blue dyes from dimethylaniline and other tertiary aromatic monoamines], Deutsches Reich Patent no. 1886 (issued:  December 15, 1877).
*  Available on-line at:  {{cite book | vauthors = Friedlaender P |title=Fortschritte der Theerfarbenfabrikation und verwandter Industriezweige |trans-title=Progress of the manufacture of coal-tar dyes and related branches of industry |date=1888 |publisher=Julius Springer |location=Berlin, Germany |volume=1 |pages=247–249 |url=https://books.google.com/books?id=3akMAAAAYAAJ&pg=PA247 |language=German |access-date=2016-10-12 |archive-date=2015-03-21 |archive-url=https://web.archive.org/web/20150321021246/http://books.google.com/books?id=3akMAAAAYAAJ&pg=PA247}}</ref>

Its use in the treatment of malaria was pioneered by [[Paul Guttmann]] and [[Paul Ehrlich]] in 1891. During this period before World War I, researchers like Ehrlich believed that drugs and dyes worked in the same way, by preferentially staining pathogens and possibly harming them. Changing the [[cell membrane]] of pathogens is how various drugs work, so the theory was partially correct, although far from complete. Methylene blue continued to be used in World War II, where it was not well-liked by soldiers, who observed, "Even at the loo, we see, we pee, [[navy blue]]."{{citation needed|date=February 2025}}

It was discovered to be an antidote to [[carbon monoxide poisoning]] and [[cyanide poisoning]] in 1933 by [[Matilda Moldenhauer Brooks|Matilda Brooks]].<ref>{{cite journal | doi = 10.1001/jama.1933.02740010061028| title = Methylene Blue As Antidote for Cyanide and Carbon Monoxide Poisoning| journal = JAMA| volume = 100| page = 59| date = January 1933| vauthors = Brooks MM}}</ref>

Methylene blue was the original prototype or [[lead compound]] for the design of many antimalarials including [[chloroquine]], antihistamines, and antipsychotics including [[chlorpromazine]].<ref>{{cite journal | vauthors = Wainwright M |title=Dyes in the development of drugs and pharmaceuticals |journal=Dyes and Pigments |date=January 2008 |volume=76 |issue=3 |pages=582–589 |doi=10.1016/j.dyepig.2007.01.015}}</ref>

== Research ==

===Malaria===
Antimalarial use of the drug has recently (2009) been revived.<ref>{{cite journal | vauthors = Coulibaly B, Zoungrana A, Mockenhaupt FP, Schirmer RH, Klose C, Mansmann U, Meissner PE, Müller O | title = Strong gametocytocidal effect of methylene blue-based combination therapy against falciparum malaria: a randomised controlled trial | journal = PLOS ONE | volume = 4 | issue = 5 | article-number = e5318 | year = 2009 | pmid = 19415120 | pmc = 2673582 | doi = 10.1371/journal.pone.0005318 | doi-access = free | bibcode = 2009PLoSO...4.5318C }}</ref> It simultaneously targets many biological processes in the [[apicomplexan]] pathogen<ref>{{cite journal | vauthors = Calderón M, Weitzel T, Rodriguez MF, Ciapponi A |title=Methylene blue for treating malaria |journal= Cochrane Database of Systematic Reviews|date=20 October 2017 |volume=2022 |issue=6 |article-number=CD012837 |doi=10.1002/14651858.CD012837 |pmc=6485827}}</ref>  though the main mechanism seems to be causing a lethal amount of redox cycling.<ref name=Lu2018/>

A 2018 meta-analysis finds that it has proven effective against ''[[P. falciparum]]'' in Africa. It effectively reduces levels of the transmission-stage [[gametocyte]] and has synergy with the standard [[artemisinin-based combination therapy]] (ACT). Its effects against other malarial species and ''P. falciparum'' populations in other locations are unclear.<ref name=Lu2018>{{cite journal | vauthors = Lu G, Nagbanshi M, Goldau N, Mendes Jorge M, Meissner P, Jahn A, Mockenhaupt FP, Müller O | title = Efficacy and safety of methylene blue in the treatment of malaria: a systematic review | journal = BMC Medicine | volume = 16 | issue = 1 | article-number = 59 | date = April 2018 | pmid = 29690878 | pmc = 5979000 | doi = 10.1186/s12916-018-1045-3 | doi-access = free }}</ref>

===Ifosfamide toxicity===
Another use of methylene blue is to treat [[ifosfamide]] [[neurotoxicity]]. Methylene blue was first reported for treatment and [[prophylaxis]] of ifosfamide neuropsychiatric toxicity in 1994. A toxic metabolite of ifosfamide, [[chloroacetaldehyde]] (CAA), disrupts the mitochondrial [[respiratory chain]], leading to an accumulation of [[nicotinamide adenine dinucleotide]] hydrogen (NADH). Methylene blue acts as an alternative [[electron acceptor]], and reverses the NADH inhibition of hepatic [[gluconeogenesis]] while also inhibiting the transformation of chloroethylamine into chloroacetaldehyde, and inhibits multiple amine oxidase activities, preventing the formation of CAA.<ref>
{{cite journal | vauthors = Alici-Evcimen Y, Breitbart WS | title = Ifosfamide neuropsychiatric toxicity in patients with cancer | journal = Psycho-Oncology | volume = 16 | issue = 10 | pages = 956–960 | date = October 2007 | pmid = 17278152 | doi = 10.1002/pon.1161 | s2cid = 27433170 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Abahssain H, Moukafih B, Essangri H, Mrabti H, Meddah B, Guessous F, Fadhil FZ, Souadka A, Errihani H | title = Methylene blue and ifosfamide-induced encephalopathy: Myth or reality? | journal = Journal of Oncology Pharmacy Practice | volume = 27 | issue = 1 | pages = 143–149 | date = January 2021 | pmid = 33153383 | doi = 10.1177/1078155220971843 }}</ref>

The dosing of methylene blue for treatment of ifosfamide neurotoxicity varies, depending upon its use simultaneously as an adjuvant in ifosfamide infusion, versus its use to reverse psychiatric symptoms that manifest after completion of an ifosfamide infusion. Reports suggest that methylene blue, up to six doses a day, has resulted in improvement of symptoms within 10 minutes to several days.<ref>
{{cite journal | vauthors = Patel PN | title = Methylene blue for management of Ifosfamide-induced encephalopathy | journal = The Annals of Pharmacotherapy | volume = 40 | issue = 2 | pages = 299–303 | date = February 2006 | pmid = 16391008 | doi = 10.1345/aph.1G114 | s2cid = 21124635 }}</ref> Alternatively, it has been suggested that intravenous methylene blue every six hours for prophylaxis during ifosfamide treatment in people with history of ifosfamide neuropsychiatric toxicity.<ref>
{{cite journal | vauthors = Dufour C, Grill J, Sabouraud P, Behar C, Munzer M, Motte J, Oberlin O, Paci A, Hartmann O | title = [Ifosfamide induced encephalopathy: 15 observations] | language = fr | journal = Archives de Pédiatrie | volume = 13 | issue = 2 | pages = 140–145 | date = February 2006 | pmid = 16364615 | doi = 10.1016/j.arcped.2005.10.021 }}</ref> Prophylactic administration of methylene blue the day before initiation of ifosfamide, and three times daily during ifosfamide chemotherapy has been recommended to lower the occurrence of ifosfamide neurotoxicity.<ref>
{{cite journal | vauthors = Aeschlimann C, Cerny T, Küpfer A | title = Inhibition of (mono)amine oxidase activity and prevention of ifosfamide encephalopathy by methylene blue | journal = Drug Metabolism and Disposition | volume = 24 | issue = 12 | pages = 1336–1339 | date = December 1996 | pmid = 8971139 | doi = 10.1016/S0090-9556(25)08471-5 }}</ref>

=== Neuropsychiatric disorders ===
Methylene blue inhibits [[monoamine oxidase]], inhibits the [[glutamatergic]] system (via inhibition of [[NO synthase]] and [[soluble guanylate cyclase]]), modulates mitochondrial function (by acting as an electron acceptor), and decreases the activation of [[inflammasome]]s [[NLRP3]] and [[NLRC4]]. As a result, it's been considered potentially useful in [[neuropsychiatric disorder]]s. In humans it has been tried for (listed in decreasing order of evidence quality): [[bipolar disorder]] (especially [[Depression (mood)|depressive]] symptoms), [[Alzheimer's disease]], [[claustrophobia]], ifosfamide encephalopathy, and [[schizophrenia]]. With methylene blue, a higher dose does not necessarily work better than a lower dose.<ref name=psych>{{cite journal | vauthors = Alda M | title = Methylene Blue in the Treatment of Neuropsychiatric Disorders | journal = CNS Drugs | volume = 33 | issue = 8 | pages = 719–725 | date = August 2019 | pmid = 31144270 | doi = 10.1007/s40263-019-00641-3 }}</ref>

== Society and culture ==
In the late 2010s and early 2020s, a [[social media]] [[trend]] emerged promoting the use of methylene blue for various medical purposes, including [[Anti-aging treatment|anti-aging]], metabolism enhancement, cognitive improvement, cancer treatment, and [[COVID-19]] treatment.<ref name="Whitehead_2022">{{Cite web | vauthors = Whitehead J |date=2022-03-18 |title=Medical expert issues warning about fish tank disinfectant craze |url=https://www.the-independent.com/life-style/health-and-families/fish-tank-cleaner-anti-aging-doctor-methylene-blue-b2038679.html |access-date=2025-03-12 |website=The Independent |language=en}}</ref><ref name="Tiller_2022">{{Cite web | vauthors = Tiller N |date=2022-04-20 |title=When Medicines Go Rogue, Part 1: Methylene Blue |url=https://skepticalinquirer.org/exclusive/when-medicines-go-rogue-methylene-blue/ |access-date=2025-03-12 |website=[[Skeptical Inquirer]] |language=en-US}}</ref><ref name="Liddell_2025">{{Cite web | vauthors = Liddell J |date=2025-02-06 |title=What was RFK Jr putting in his drink mid-flight? |url=https://www.independent.co.uk/news/world/americas/us-politics/rfk-jr-drinking-flight-methylene-blue-b2693495.html |access-date=2025-03-12 |website=The Independent |language=en}}</ref><ref name="Stebbing_2025">{{Cite web | vauthors = Stebbing J |date=2025-01-27 |title=From methylene blue to vitamin E, here's why health and wellness supplements are no silver bullet for cancer |url=https://theconversation.com/from-methylene-blue-to-vitamin-e-heres-why-health-and-wellness-supplements-are-no-silver-bullet-for-cancer-247847 |access-date=2025-03-12 |website=The Conversation |language=en-US}}</ref> Currently there is no scientific consensus on, and no FDA approval for, its effectiveness and safety for these purposes.<ref name="Whitehead_2022" /><ref name="Tiller_2022" /><ref name="Stebbing_2025" /> Medical experts cautioned that methylene blue can be toxic in high doses and may [[Drug interaction|interact with other medications]], potentially reducing their effectiveness or causing unforeseen side effects. Therefore, it should only be used under a doctor's prescription.<ref name="Whitehead_2022" /><ref name="Tiller_2022" />

This trend probably started following the publication of a few scientific papers exploring the potential of methylene blue for treating some medical conditions,<ref name="Whitehead_2022" /> such as [[progeria]],<ref>{{cite journal | vauthors = Xiong ZM, Choi JY, Wang K, Zhang H, Tariq Z, Wu D, Ko E, LaDana C, Sesaki H, Cao K | title = Methylene blue alleviates nuclear and mitochondrial abnormalities in progeria | journal = Aging Cell | volume = 15 | issue = 2 | pages = 279–290 | date = April 2016 | pmid = 26663466 | pmc = 4783354 | doi = 10.1111/acel.12434 }}</ref> and [[skin aging]].<ref>{{cite journal | vauthors = Xiong ZM, O'Donovan M, Sun L, Choi JY, Ren M, Cao K | title = Anti-Aging Potentials of Methylene Blue for Human Skin Longevity | journal = Scientific Reports | volume = 7 | issue = 1 | article-number = 2475 | date = May 2017 | pmid = 28559565 | pmc = 5449383 | doi = 10.1038/s41598-017-02419-3 | bibcode = 2017NatSR...7.2475X }}</ref> It was also explored as part of anticancer [[photodynamic therapy]] using lasers.<ref>{{cite journal | vauthors = Taldaev A, Terekhov R, Nikitin I, Melnik E, Kuzina V, Klochko M, Reshetov I, Shiryaev A, Loschenov V, Ramenskaya G | title = Methylene blue in anticancer photodynamic therapy: systematic review of preclinical studies | journal = Frontiers in Pharmacology | volume = 14 | article-number = 1264961 | date = 2023-09-28 | pmid = 37841915 | pmc = 10568458 | doi = 10.3389/fphar.2023.1264961 | doi-access = free }}</ref> One systematic review of the studies expresses optimism but emphasizes the need for more extensive research to confirm methylene blue's clinical applications.<ref>{{cite journal | vauthors = Xue H, Thaivalappil A, Cao K | title = The Potentials of Methylene Blue as an Anti-Aging Drug | journal = Cells | volume = 10 | issue = 12 | page = 3379 | date = December 2021 | pmid = 34943887 | pmc = 8699482 | doi = 10.3390/cells10123379 | doi-access = free }}</ref> Another review takes a more critical stance, stating that "it is obvious that the clinical use of [methylene blue] represents a rather controversial problem given the heterogeneity of available data and the lack of preclinical data, which is in conflict with standards of safe use of such substances in human medicinal practice".<ref>{{cite journal | vauthors = Bužga M, Machytka E, Dvořáčková E, Švagera Z, Stejskal D, Máca J, Král J | title = Methylene blue: a controversial diagnostic acid and medication? | journal = Toxicology Research | volume = 11 | issue = 5 | pages = 711–717 | date = October 2022 | pmid = 36337249 | pmc = 9618115 | doi = 10.1093/toxres/tfac050 }}</ref>

In January 2025, [[Robert F. Kennedy Jr.|Robert F. Kennedy Jr]], then the [[United States Secretary of Health and Human Services|U.S. health secretary]] nominee, was filmed adding droplets of an unidentified blue liquid to his drink during a flight.<ref>{{Cite news |title=The Right Chemistry: TikTok is crazy for methylene blue, but not for the right reasons |url=https://www.montrealgazette.com/opinion/columnists/article887766.html}}</ref> While many have speculated that it was methylene blue, Kennedy has not addressed the claims.<ref name="Liddell_2025" /><ref>{{Cite news | vauthors = Mahdawi A |date=2025-02-11 |title=Did RFK Jr really drink fish medicine? He definitely has weird ideas about 'making America healthy again' |url=https://www.theguardian.com/commentisfree/2025/feb/11/did-rfk-jr-really-drink-fish-medicine-definitely-has-weird-ideas-making-america-healthy-again |access-date=2025-03-12 |work=The Guardian |language=en-GB |issn=0261-3077}}</ref><ref>{{Cite news |date=2025-02-06 |title=Robert F. Kennedy Jr.'s viral video sparks mystery over blue liquid. What Is Methylene Blue? |url=https://economictimes.indiatimes.com/magazines/panache/rfk-jr-s-viral-video-sparks-mystery-over-blue-liquid-what-is-methylene-blue/articleshow/117987350.cms?from=mdr |access-date=2025-03-12 |work=[[The Economic Times]] |issn=0013-0389}}</ref>

== References ==
{{Reflist}}

== External links ==
{{Commons}}
* {{cite web | url = https://druginfo.nlm.nih.gov/drugportal/name/methylthioninium%20chloride | archive-url = https://web.archive.org/web/20200411015505/https://druginfo.nlm.nih.gov/drugportal/name/methylthioninium%2520chloride | archive-date = April 11, 2020 | publisher = U.S. National Library of Medicine | work = Drug Information Portal | title = Methylene blue }}
* {{cite web | title=Methylene blue test | website=MedlinePlus | url=https://medlineplus.gov/ency/article/003412.htm }}

{{Antidotes}}
{{Stains}}
{{Glutamatergics}}
{{Monoamine metabolism modulators}}
{{Tricyclics}}
{{Portal bar|Medicine}}
{{Authority control}}

{{DEFAULTSORT:Methylene Blue}}
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