Methylene Blue Liver Safety: What 2026 Research Shows

Written by the NooBlue editorial team. NooBlue sells methylene blue only. This page is general information, not medical advice. Every study below is listed in the sources at the end.

A single 500 mg oral dose. That is what healthy volunteers took in the absorption study most often cited in methylene blue liver discussions, 100 times the 5 mg in one NooBlue capsule. Most of what is published about methylene blue and the liver comes from hospital medicine, poisoning models and high-dose studies. Very little describes what a small daily supplement does.

This guide sets out how the body handles methylene blue, how supplement amounts compare with the doses in the research, what the liver evidence shows and where it runs out, who should be careful, and the wider safety rules that matter more than the liver for most people.

Methylene blue safety: the rules that matter most

Before the liver, the bigger picture. The prescribing label for injectable methylene blue (ProvayBlue) is the most detailed safety document for the compound, and its warnings apply in principle to anyone taking it by mouth, even though supplement amounts are far smaller than hospital doses.

• Serotonergic drugs and opioids. The label’s boxed warning says methylene blue may cause serious or fatal serotonin syndrome when combined with serotonergic drugs and opioids, and tells doctors to avoid combining it with SSRIs, SNRIs, MAOIs and opioids. The reason is enzyme inhibition: Ramsay, Dunford and Gillman (British Journal of Pharmacology, 2007) found methylene blue to be a potent, reversible inhibitor of MAO-A, the enzyme that breaks down serotonin. Our pages on methylene blue and serotonin syndrome and methylene blue interactions list the drug classes.
• G6PD deficiency. The label says treating people with G6PD deficiency can cause severe hemolysis (red blood cell breakdown) and lists it as a reason not to use the drug at all. Our G6PD guide explains why.
• Pregnancy and breastfeeding. The label says methylene blue may cause fetal harm, and advises stopping breastfeeding for up to 8 days after an injectable dose because of possible genotoxicity. Do not take a supplement while pregnant or breastfeeding.
• Kidney and liver function. Both organs affect how long methylene blue stays in the body, which the sections below explain.
• Tests and monitors. At hospital doses, methylene blue in the blood can make pulse oximeters read oxygen levels too low, and because it passes into urine it can interfere with urine dipstick tests that rely on a blue indicator. Tell your care team you take it before a procedure or lab test.

Our checklist of who should not take methylene blue and our guide to methylene blue side effects cover the rest.

How the body clears methylene blue

Absorption. Methylene blue is well absorbed by mouth. In a crossover study of 16 healthy volunteers, Walter-Sack and colleagues (European Journal of Clinical Pharmacology, 2009) gave 50 mg intravenously and 500 mg by mouth a week apart and measured an absolute oral bioavailability of 72.3%. High absorption is why an oral dose does anything at all, and it is also why the amount your body has to clear is real rather than theoretical.

The liver’s role. The ProvayBlue label says methylene blue is extensively metabolized in the liver. In lab tests it is processed by three cytochrome P450 enzymes (CYP1A2, CYP2C19 and CYP2D6), but the main route appears to be conjugation by UGT enzymes, including UGT1A4 and UGT1A9. The body also turns a small share of it into azure B, a related dye. In rats, methylene blue given into the gut reached higher concentrations in the intestinal wall and the liver than the same dose given into a vein, which fits with the liver seeing oral doses first (Peter 2000).

Excretion. Methylene blue leaves the body largely in urine, much of it as its colorless reduced form, leucomethylene blue (IARC volume 108). The blue remainder is why urine turns blue or green. Our guide to methylene blue urine color explains what to expect.

How long it stays. Estimates differ. The injectable label gives a half-life of about 24 hours in humans, while an earlier small study from Bern estimated a terminal half-life of 5.25 hours after an intravenous dose (Peter 2000). Our page on methylene blue half-life goes through the numbers.

Other drugs can change the level. In the Walter-Sack study, taking methylene blue with the antimalarial chloroquine significantly raised its plasma concentration. Because several liver enzymes handle methylene blue, other medicines could shift its levels too, which is one more reason to run your medicine list past a pharmacist.

Supplement doses vs the doses in liver research

This comparison clears up most of the confusion. Each row is one dose, so the numbers are directly comparable.

When a paper discusses methylene blue alongside liver failure, transplant surgery or poisoning, it is usually describing a patient who is already very ill, given 10 to 100 times a supplement serving, often straight into a vein. Carrying either the benefits or the harms from that setting over to a 5 mg capsule with breakfast is a big leap in both directions.

What the liver evidence shows, and what it doesn’t

Rodent toxicity studies

The largest safety studies of oral methylene blue were run in rats and mice. IARC’s volume 108 review summarizes a 90-day study at 25 to 200 mg per kg by mouth: the main effects were on red blood cells, with methemoglobin formation and a regenerative anemia. Mice also showed blood-cell production in the liver at 100 mg per kg and above, and iron pigment in the liver’s Kupffer cells at 50 mg per kg and above, which the reviewers read as signs of red blood cell breakdown. Per kg of body weight, these doses are hundreds to thousands of times a 5 mg supplement serving, and the liver changes followed the blood effects rather than showing direct liver damage.

Hospital reports

The injectable label lists elevated liver enzymes and raised bilirubin among the reactions reported after methylene blue class products. It also explains that hemolysis during treatment can raise indirect bilirubin, so some bilirubin rises reflect red blood cell breakdown rather than the liver itself. The label does not give a rate for the liver enzyme reports, and they come from hospital use at intravenous doses.

Animal protection models

In a study in International Immunopharmacology (Chen 2015), rats were poisoned with the herbicide paraquat, which causes severe oxidative liver damage. Rats given methylene blue at 2 mg per kg by injection two hours later had less tissue damage, lower liver enzymes (ALT and alkaline phosphatase) and higher antioxidant enzyme levels. That shows antioxidant activity in liver tissue under extreme stress, in rats. It is not evidence that a daily capsule protects a human liver, and methylene blue is not a liver supplement.

Case reports

A 2010 case report in Transplantation Proceedings described methylene blue given to a 15-year-old in the first days after a liver transplant, to improve low blood oxygen caused by a lung complication of her liver disease (Roma 2010). A single case report cannot establish an effect, and it describes hospital care, not supplement use.

What is missing

There is no long-term controlled human trial of low-dose oral methylene blue with liver enzymes or liver imaging as outcomes. Nothing published supports using it for any liver condition. The absence of data is not evidence of harm, and it is not evidence of safety either. Our overview of what human trials of methylene blue have shown and our methylene blue research statistics page put this in the wider context.

Who should be cautious about methylene blue and the liver

• People with liver disease or reduced liver function. The label tells doctors to monitor patients with any liver impairment for longer, for toxicity and drug interactions, because clearance is delayed. If that applies to you, talk to your doctor before taking methylene blue, and do not start without their agreement.
• People with kidney disease. The label reports significantly higher methylene blue concentrations in people with reduced kidney function and lowers the injectable dose for moderate or severe kidney impairment. The same conversation with your doctor applies.
• Anyone taking serotonergic medicines or opioids. This is the interaction that matters most, whatever the state of your liver. Do not combine them.
• People with G6PD deficiency. Do not take methylene blue. The risk is to red blood cells, not the liver, but it is the clearest exclusion of all.
• Regular drinkers. No study has tested methylene blue with alcohol. Our article on methylene blue and alcohol covers what is known.

Know the general warning signs of a liver problem from any cause. MedlinePlus lists yellowing of the skin and eyes, changes in the color of stool and urine, swelling of the abdomen and legs, and bruising easily, and notes that liver problems sometimes cause no symptoms. Methylene blue already tints urine blue-green, so that sign is harder to read. If you notice any of these, stop and see a doctor, and tell them what you take. Our guide to whether methylene blue is safe to take daily covers long-term use.

How to keep your exposure low

• Use the smallest amount. Methylene blue has a hormetic dose response, with opposite effects at low and high doses (Rojas 2012), so more is not better, and a smaller dose leaves less for your liver and kidneys to clear. Our guide to how many mg of methylene blue per day covers amounts.
• Take one product at a time, with food. NooBlue’s capsule label says one capsule daily with food.
• Check your medicines and your drinks. Interactions carry more risk than the liver does. Our pages on methylene blue and coffee and methylene blue and Adderall cover two common questions.
• Buy USP-grade methylene blue, not lab or aquarium dye. The USP monograph requires USP methylene blue to contain 97.0% to 103.0% methylene blue on the dried basis, and dye made for staining or fish tanks is not made to that standard. Our guide to lab grade vs pharmaceutical grade methylene blue explains the difference.

NooBlue uses USP-grade methylene blue in all three formats. The lab report on our product pages covers the methylene blue ingredient (identity and heavy metals), not every finished batch. Our capsules are 5 mg, $37.99 for 60, or $0.63 per serving (as of Sep 2026). The 1% methylene blue drops give 0.5 mg per drop, $29.99 for 50 mL, and our tablets vs liquid comparison covers the format choice. To compare other brands, see our best methylene blue supplements comparison, or browse the NooBlue shop.

Frequently asked questions

Does methylene blue harm the liver?

No published human study has shown liver injury from oral methylene blue at supplement amounts, but no long-term study has monitored liver markers in people taking it daily. The injectable label lists elevated liver enzymes among reactions reported in hospital use, and it asks for longer monitoring in people with liver impairment because clearance is slower. So the position is “no signal at supplement doses, limited data,” not “proven safe for the liver.”

Is methylene blue harmful to humans?

It can be, in the wrong person or at the wrong dose. It can cause serious serotonin syndrome with serotonergic drugs and opioids, severe red blood cell breakdown with G6PD deficiency, and fetal harm in pregnancy. At high intravenous doses the label describes nausea, chest pain, dizziness, confusion and other effects. For healthy adults who avoid those situations, the published data at supplement amounts do not show a clear harm, although long-term studies are missing.

What is the main warning on methylene blue’s label?

The injectable label carries a boxed warning that methylene blue may cause serious or fatal serotonin syndrome when used with serotonergic drugs and opioids, and it says to avoid combining it with SSRIs, SNRIs, MAOIs and opioids. That warning is why NooBlue tells anyone on those medicines not to take methylene blue.

Can methylene blue raise liver enzymes?

Elevated liver enzymes are listed among reactions reported after methylene blue class products in hospital use, with no rate given. There are no data on supplement amounts. If you already have liver tests for another reason, keep having them and tell whoever orders them that you take methylene blue.

If you have fatty liver, can methylene blue help?

No. There is no clinical evidence for methylene blue in fatty liver, and it is not a treatment for any liver condition. The animal study showing liver protection used acute herbicide poisoning and injected doses. If you have a liver condition, talk to your doctor before taking any supplement.

Who should not take methylene blue?

People with G6PD deficiency, anyone taking SSRIs, SNRIs, MAOIs, opioids or other serotonergic medicines, people who are pregnant or breastfeeding, anyone under 18, and anyone with liver or kidney disease who has not discussed it with their doctor. Our full checklist of who should not take methylene blue covers each group.

Is methylene blue safe for the kidneys?

Methylene blue leaves the body largely in urine, so the kidneys carry much of the load. The injectable label reports significantly higher blood levels in people with reduced kidney function and lowers the hospital dose for moderate or severe kidney impairment. No study has shown kidney injury from low oral doses in healthy people, but if you have kidney disease, talk to your doctor first.

Why do I feel weird after taking methylene blue?

At hospital doses, the label lists confusion, dizziness and changes in vision, and advises against driving until they pass. Headache and nausea are among the most common reactions in its trial. If you take a serotonergic medicine or an opioid and feel agitated, shaky, sweaty, feverish or have a racing heart after methylene blue, seek medical care right away, because those can be signs of serotonin syndrome. For milder oddness at supplement amounts, stop and talk to your doctor or pharmacist before trying again at a lower amount.

Why don’t doctors recommend methylene blue?

Mostly because the evidence for low-dose daily use is thin, and because it needs a medication check first. The best-known human study gave 26 healthy adults a single 280 mg dose and measured them for one hour. Our article on why doctors don’t prescribe methylene blue goes into more depth.

Does methylene blue affect blood pressure?

At hospital doses it can move in both directions. The injectable label lists high blood pressure among reactions reported after methylene blue class products, and low blood pressure has been reported after single doses of 3 mg per kg or more. Supplement amounts are far lower. Our article on methylene blue and blood pressure explains the research.

What is the best methylene blue to start with?

NooBlue’s 5 mg capsules are our pick for a first bottle: a fixed, low amount of USP-grade methylene blue with 10 mg of vitamin C, 60 capsules for $37.99 (as of Sep 2026), one a day with food. NooBlue makes them, so compare other brands too. If you would rather not swallow capsules, our 10 mg methylene blue gummies ($49.99 for 60) and the 1% drops are the other two formats.

Sources

1. PROVAYBLUE (methylene blue) injection, prescribing information (American Regent). DailyMed (boxed warning, G6PD, pregnancy, lactation, hepatic and renal impairment, metabolism, half-life, adverse reactions, overdose, test interference).
2. Walter-Sack I, Rengelshausen J, Oberwittler H, et al. High absolute bioavailability of methylene blue given as an aqueous oral formulation. European Journal of Clinical Pharmacology. 2009;65(2):179-189. PubMed 18810398
3. Peter C, Hongwan D, Küpfer A, Lauterburg BH. Pharmacokinetics and organ distribution of intravenous and oral methylene blue. European Journal of Clinical Pharmacology. 2000;56(3):247-250. PubMed 10952480
4. IARC Monographs volume 108 (Some drugs and herbal products): Methylene blue (absorption, excretion, tissue distribution, 90-day rodent toxicity).
5. Ramsay RR, Dunford C, Gillman PK. Methylene blue and serotonin toxicity: inhibition of monoamine oxidase A (MAO A) confirms a theoretical prediction. British Journal of Pharmacology. 2007;152(6):946-951. PubMed 17721552
6. Chen JL, Dai L, Zhang P, et al. Methylene blue attenuates acute liver injury induced by paraquat in rats. International Immunopharmacology. 2015;28(1):808-812. PubMed 25943564
7. Roma J, Balbi E, Pacheco-Moreira L, et al. Methylene blue used as a bridge to liver transplantation postoperative recovery: a case report. Transplantation Proceedings. 2010;42(2):601-604. PubMed 20304203
8. Rojas JC, Bruchey AK, Gonzalez-Lima F. Neurometabolic mechanisms for memory enhancement and neuroprotection of methylene blue. Progress in Neurobiology. 2012;96(1):32-45. PubMed 22067440
9. Rodriguez P, Zhou W, Barrett DW, et al. Multimodal randomized functional MR imaging of the effects of methylene blue in the human brain. Radiology. 2016;281(2):516-526. PMC5084971
10. United States Pharmacopeia. Methylene Blue monograph (definition: 97.0% to 103.0% on the dried basis).
11. MedlinePlus. Liver Diseases (symptoms).
12. NooBlue product pages for our label facts: capsules, gummies and drops.