Transparency: This article is an overview of approvals, side effects and safety warnings, not a recommendation to use methylene blue. It deliberately contains no dosing information. It is based on the EU product information for Proveblue (EMA), the US label for Provayblue (FDA), Germany’s prescription ordinance, warnings from Germany’s Verbraucherzentrale and Australia’s TGA, and reviews indexed in PubMed, all accessed on 15 Oct 2026. All sources are listed at the end. No affiliate links. More on methodology
Our own self-experiment: Max took methylene blue over 16 months and compared it against his Whoop data. Result: no higher HRV, slightly less deep sleep and slightly lower recovery. All data, limitations and safety notes are in the methylene blue self-experiment with 254 nights of Whoop data. This article adds the medical side.
Key points
- What it is: methylene blue (methylthioninium chloride) is a blue dye and a medicine. It was the first synthetic antimalarial.
- Authorised in the EU: as an injection for acute methaemoglobinaemia (Proveblue, since 2011) and as a tablet to improve visibility during colonoscopy (since 2020). Both are prescription-only.
- Not approved: anything methylene blue is promoted for on TikTok and in biohacking forums, such as focus, mood, energy or anti-ageing.
- Biggest risk: serotonin syndrome in combination with antidepressants and certain painkillers. Methylene blue is itself a potent MAO inhibitor.
- Other exclusions: G6PD deficiency, hypersensitivity to thiazine dyes, pregnancy only if clearly necessary.
- Most visible side effect: blue-green urine and blue skin. Looks harmless, but according to the label it can hinder the diagnosis of cyanosis.
- Products sold online: mostly laboratory chemicals that, according to Germany’s Verbraucherzentrale, lack the purity needed for consumption.
What is methylene blue?
The drug name of methylene blue is methylthioninium chloride. It is a synthetic dye that was already used medically in the 19th century. A systematic review in BMC Medicine (2018) calls it “the first synthetic antimalarial to be discovered”, used “during the late 19th and early 20th centuries against all types of malaria”.
The pharmacological fact that matters most for safety: according to the EU label, “Methylthioninium chloride is a potent reversible inhibitor of monoamine oxidase”, i.e. an MAO inhibitor. The main risk follows from that, see below.
What methylene blue is authorised for
1. Methaemoglobinaemia: the emergency antidote
In methaemoglobinaemia, part of the blood’s haemoglobin is altered so that it no longer carries oxygen. Certain medicines and chemicals can cause it. Methylene blue is the standard antidote.
In the EU, Proveblue has been authorised for this EU-wide since 6 May 2011. Its indication: “Acute symptomatic treatment of medicinal and chemical products-induced methaemoglobinaemia”, in adults, children and adolescents. Proveblue is a solution for injection given slowly into a vein. According to the EMA, “It can only be obtained with a prescription and must be given by a healthcare professional.” The label says it is intended for acute use in emergency situations in hospital only.
A 2026 review in the British Journal of Haematology confirms “intravenous methylene blue remaining first-line treatment for symptomatic cases”. In the US, the equivalent product Provayblue is approved for acquired methemoglobinemia.
2. Colonoscopy: a dye for better visibility
Since 19 August 2020 there has been a second EU authorisation: methylthioninium chloride tablets (formerly Lumeblue, now listed as “Methylthioninium chloride Cosmo”). According to the EMA, they are “used in adults as a dye to help doctors see the lining of the colon (large bowel) more clearly and improve detection of lesions”. This product is also prescription-only. According to the EMA it must not be used with G6PD deficiency, or during pregnancy and breastfeeding.
3. Surgery and diagnostics: a marking dye
In surgery, methylene blue is used as a dye, for example to locate the sentinel lymph node in breast cancer. A 2018 meta-analysis in PLoS One reached a mixed conclusion: methylene blue alone has “an acceptable identification rate but an excessive false negative rate”, and “caution is warranted when using methylene blue dye alone as the mapping method”.
What is being researched but not approved
- Septic shock: A meta-analysis of six randomised trials with 302 patients (Critical Care Explorations, 2024) found that methylene blue may reduce short-term mortality and hospital length of stay, both rated as low-certainty evidence. The authors call for larger trials.
- Alzheimer’s disease: A phase 3 trial of the methylene blue derivative LMTM (Lancet, 2016, 891 participants) was negative: “The primary analysis for this study was negative, and the results do not suggest benefit of LMTM as an add-on treatment.”
- Malaria: Historically used. According to the 2018 BMC Medicine review, methylene blue has been considered “a potentially useful partner drug for artemisinin-based combination therapy”. It is not authorised for this in the EU.
Methylene blue as a biohacking trend
On social media, methylene blue is promoted as a “mitochondria booster”: more energy, a clearer head, better mood, higher HRV. In September 2025, Australia’s medicines regulator TGA issued a safety advisory about “the increasing importation and use of unregistered oral methylene blue (methylthioninium chloride) products”, promoted for unapproved uses “such as cognitive enhancement, mood improvement, and anti-ageing effects”. The TGA will notify Border Force to seize and destroy non-compliant products.
None of these uses is approved. What the published studies on cognitive effects actually show, and what they don’t, is summarised in Max’s self-experiment, together with his own Whoop data. It also explains why a tracker alone can only partly capture such effects.
Side effects according to the label
The following comes from the EU product information for Proveblue and refers to intravenous use in hospital.
Very common (more than 1 in 10):
- blue skin discoloration
- blue-green urine (chromaturia)
- sweating
- nausea
- dizziness
Most commonly reported in clinical trials overall: “dizziness, paraesthesia, dysgeusia, nausea, skin discoloration, chromaturia, sweating, injection site pain and pain in extremity.”
More serious:
- “Intravenous injection of methylthioninium chloride has occasionally caused hypotension and cardiac arrhythmias, and such disorders might prove fatal on rare occasions.”
- Haemolytic anaemia (frequency not known), especially with G6PD deficiency.
- Anaphylactic reactions (frequency not known).
- Skin photosensitivity under strong light sources.
Two effects that distort measurements:
- The blue colouring of skin, urine and faeces “may hinder a diagnosis of cyanosis”, according to the EU label.
- Pulse oximetry may give a false oxygen saturation reading during administration. The FDA label says it may result in “an underestimation of the oxygen saturation reading”.
The key safety points
Serotonin syndrome with antidepressants and opioids
This is the point most often lost in the biohacking context. The EU label states:
“Methylthioninium chloride may cause serious or fatal serotonergic syndrome when used in combination with serotonergic drugs. Avoid concomitant use of methylthioninium chloride with selective serotonin reuptake inhibitors (SSRIs), serotonin and norepinephrine reuptake inhibitors (SNRIs), monoamine oxidase inhibitors and opioids”
As examples, the label names bupropion, buspirone, clomipramine, mirtazapine and venlafaxine, and the opioids tramadol, fentanyl, pethidine and dextromethorphan (the latter is also found in cough suppressants).
The FDA puts this warning at the very top of the US Provayblue label as a boxed warning, the most prominent form of warning in US prescribing information.
G6PD deficiency
With a deficiency of the enzyme glucose-6-phosphate dehydrogenase, methylene blue is contraindicated according to both the EMA and the FDA, because of the risk of haemolytic anaemia (destruction of red blood cells). According to a 2008 review in the Lancet, G6PD deficiency “is the most common human enzyme defect, being present in more than 400 million people worldwide”.
Other contraindications
According to the Proveblue label, also:
- hypersensitivity to methylthioninium chloride or other thiazine dyes
- nitrite-induced methaemoglobinaemia during treatment of cyanide poisoning
- methaemoglobinaemia due to chlorate poisoning
- NADPH reductase deficiency
Pregnancy and breastfeeding
- EMA (Proveblue): animal studies have shown reproductive toxicity, the potential risk for humans is unknown. Proveblue “should not be used during pregnancy unless clearly necessary, e.g. in life-threatening methaemoglobinaemia”. Breastfeeding should be discontinued for up to 8 days after treatment.
- FDA (Provayblue): “may cause fetal harm when administered to a pregnant woman”.
- TGA: “Methylene blue should not be used during pregnancy. It has been associated with birth defects in both humans and animals.”
- According to the EMA, the colonoscopy tablets must not be taken during pregnancy or breastfeeding at all.
Legal status in Germany and the quality question
Prescription requirement: Annex 1 of Germany’s prescription ordinance (AMVV) lists methylthioninium salts “for parenteral use in humans”, i.e. injections and infusions. The two EU-authorised products are prescription-only anyway, according to the EMA.
What is sold online: The drops and capsules sold in web shops and by influencers are not authorised medicines. Germany’s Verbraucherzentrale (consumer advice centre) writes (as of August 2026) that laboratory chemicals such as methylene blue are being promoted like dietary supplements, especially on social media, that these products are not intended for consumption and therefore lack the necessary purity, and that this can be very dangerous.
Why purity is a real issue here: In its assessment report for Proveblue, the EMA noted: “Methylthioninium chloride has a strong affinity for metals, and it is difficult to manufacture a substance that complies with the Ph Eur monograph.” Proveblue qualified for the centralised EU procedure precisely because there was no commercial source of the active substance in pharmacopoeia quality and the manufacturer had developed a metals-free synthesis route. The report explicitly distinguishes this substance from “other less pure grades of methylthioninium chloride”.
In September 2025, the Blue Ridge Poison Center in Virginia reported “an increase in calls” about exposure to oral methylene blue. It adds: “because these products are sold as dietary supplements, they are not subject to U.S. Food and Drug Administration (FDA) standards or testing, meaning concentration and purity may vary greatly between products.”
Verdict
Methylene blue is a real, old medicine with a clear role: as an emergency antidote for methaemoglobinaemia and as a dye in diagnostics and surgery. There it is given in hospital, by healthcare professionals, in pharmaceutical-grade quality.
The biohacking trend uses the same substance for purposes nobody has approved, mostly in the form of laboratory chemicals. The risks stay the same: an MAO inhibitor that can trigger life-threatening serotonin syndrome with common antidepressants and painkillers, and a dye that can destroy red blood cells in people with G6PD deficiency. If you take medication or are unsure, talk to a doctor or pharmacist first.
What a self-experiment with methylene blue shows in tracker data, and what it doesn’t, is in the methylene blue self-experiment.
Sources
- EMA, Methylthioninium chloride Proveblue, EPAR overview (indication, authorisation 6 May 2011, prescription status): ema.europa.eu
- EMA, Proveblue product information / SmPC (contraindications, warnings, interactions, pregnancy, adverse reactions): ema.europa.eu (PDF)
- EMA, Proveblue public assessment report (metal affinity, purity): ema.europa.eu (PDF)
- EMA, Methylthioninium chloride Cosmo (formerly Lumeblue), colonoscopy tablets, authorised 19 Aug 2020: ema.europa.eu
- FDA, Provayblue prescribing information, revised 02/2024 (boxed warning, contraindications, pregnancy, pulse oximetry): accessdata.fda.gov (PDF)
- German prescription ordinance (AMVV), Annex 1 (German): gesetze-im-internet.de
- Verbraucherzentrale, “Gesundheitsgefahr durch illegale Stoffe”, as of 10 Aug 2026 (German): verbraucherzentrale.de
- TGA (Australia), safety advisory on imported unregistered methylene blue products, 25 Sep 2025: tga.gov.au
- Blue Ridge Poison Center / UVA, ToxTalks “Oral methylene blue”, September 2025: med.virginia.edu (PDF)
- Lu G et al.: Efficacy and safety of methylene blue in the treatment of malaria: a systematic review. BMC Med 2018;16:59. PubMed 29690878
- Fernando SM et al.: Methylene Blue in Septic Shock: A Systematic Review and Meta-Analysis. Crit Care Explor 2024;6(7):e1110. PubMed 38904978
- Gauthier S et al.: Efficacy and safety of tau-aggregation inhibitor therapy in patients with mild or moderate Alzheimer’s disease, phase 3. Lancet 2016;388:2873–2884. PubMed 27863809
- Li J et al.: Sentinel lymph node biopsy mapped with methylene blue dye alone in patients with breast cancer, systematic review and meta-analysis. PLoS One 2018;13(9):e0204364. PubMed 30235340
- Twine AJ et al.: Methaemoglobinaemia: From pathophysiology to contemporary clinical management. Br J Haematol 2026;209(3):900–910. PubMed 42381511
- Cappellini MD, Fiorelli G: Glucose-6-phosphate dehydrogenase deficiency. Lancet 2008;371:64–74. PubMed 18177777
This article is not medical advice and does not replace a conversation with a doctor or pharmacist. It deliberately contains no dosing information. As of 15 October 2026.