Methylene blue side effects.
The short answer
The most common side effect is harmless and visible: blue or green urine and a briefly blue tongue. The serious one is an interaction. Methylene blue inhibits an enzyme that breaks down serotonin, so taken with serotonergic antidepressants it can cause serotonin syndrome, which is why the prescription form carries a boxed warning12. It is also unsuitable for people with G6PD deficiency1.
Key takeaways
- Expected and harmless: blue-green urine, a blue tongue, staining on fabric1.
- Serious: serotonin syndrome with SSRIs, SNRIs, MAOIs and other serotonergic drugs12.
- Do not take it with G6PD deficiency (risk of hemolytic anemia)1.
- Pregnancy and nursing: the prescription label advises against routine use1.
- More is not better: methylene blue follows a hormetic dose curve3.
The expected, harmless effects
Methylene blue is a dye, and it behaves like one. Urine often turns blue or green, and the tongue is tinted for a while after a dose. The prescription label lists chromaturia (colored urine) and skin discoloration among its common reactions1.
Other reactions listed on the prescription label include a change in taste, feeling hot, dizziness, sweating, nausea and headache1. That label covers the intravenous drug at medical doses, so it is the most complete safety reference available, not a description of a typical oral serving.
The serious one: serotonin syndrome
Methylene blue inhibits monoamine oxidase A, the enzyme that breaks down serotonin. Combined with drugs that raise serotonin, levels can climb too high. That is serotonin syndrome, which can cause agitation, confusion, a fast heartbeat, high temperature and muscle twitching, and can be dangerous.
The prescription label carries a boxed warning against combining methylene blue with serotonergic drugs1. A systematic review found 50 previously published cases. Every one involved a person also taking serotonergic antidepressants, and all followed methylene blue given by injection or infusion, mostly during surgery. The authors then reported a new case that followed an oral product2.
Serotonergic drugs include SSRIs, SNRIs, tricyclic antidepressants, MAO inhibitors and several others. By the same mechanism, ask before combining methylene blue with serotonergic supplements such as 5-HTP or St. John’s wort. If you take any of these, do not start methylene blue without your doctor.
G6PD deficiency
Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an inherited condition that leaves red blood cells vulnerable to oxidative stress. The prescription label lists it as a contraindication because methylene blue can trigger hemolytic anemia in these patients1. If you have it, or are unsure and have a family history, ask before taking methylene blue.
Pregnancy, nursing, kidneys and liver
The prescription label states that methylene blue may cause fetal harm, advises pausing breastfeeding after treatment, and asks for longer monitoring in people with reduced kidney or liver function because the drug clears more slowly1. If any of these apply, talk to your doctor first.
Why more is not better
Methylene blue’s effects follow a hormetic dose curve. In research, responses rose with dose up to a point, then fell, and at higher doses dropped below baseline; it increased a key mitochondrial enzyme at intermediate doses and decreased it at higher ones3. Measure the serving, and do not chase a stronger effect with a bigger dose.
Common questions
Is blue urine from methylene blue harmful?
No. It is the dye leaving your body, an expected effect listed on the prescription label. It fades once you stop.
Is methylene blue safe?
It has a long medical history, but it is not for everyone. Avoid it with serotonergic medicines, with G6PD deficiency, and in pregnancy, and ask your doctor first if you have kidney or liver problems or take any regular medication.
Can I take methylene blue with an SSRI?
Not without your doctor. The combination can cause serotonin syndrome, and the prescription form of methylene blue carries a boxed warning about it.
Does methylene blue affect the kidneys?
The prescription label asks for longer monitoring in people with reduced kidney function, because methylene blue clears more slowly. If you have kidney disease, talk to your doctor before using it.
Where Thriviom fits
Methylene Blue 1%
Every amount printed on the label, every batch tested by an independent lab, and the report for your lot is yours to look up. Read the full ingredient guide first if you are weighing it up.
Sources
- U.S. Food and Drug Administration (label) PROVAYBLUE (methylene blue) injection, USP: Full Prescribing Information. Drugs@FDA, 2016.
- Zuschlag ZD, Warren MW, Schultz SK. Serotonin Toxicity and Urinary Analgesics: A Case Report and Systematic Literature Review of Methylene Blue-Induced Serotonin Syndrome. Psychosomatics, 2018.
- Bruchey AK, Gonzalez-Lima F. Behavioral, Physiological and Biochemical Hormetic Responses to the Autoxidizable Dye Methylene Blue. American Journal of Pharmacology and Toxicology, 2008.
This article is for general education and is not medical advice. Talk to your doctor or pharmacist before starting a supplement, especially if you are pregnant, nursing, or take any medication. These statements have not been evaluated by the Food and Drug Administration. Thriviom products are not intended to diagnose, treat, cure, or prevent any disease.