Why Does Methylene Blue Turn Urine Blue or Green?

Written by Lize Bührmann, founder of Pharmatropia.

Short answer: methylene blue may turn urine blue or green because some of the compound leaves the body through the kidneys. Yellow urine mixed with blue pigment can look green. The colour can be startling, but on its own it does not prove that a product is effective, pure or “detoxing” the body.

The 2023 US prescribing information for medical methylene blue reports that approximately 40% is excreted unchanged in urine. It also warns that the blue dye can interfere with urine tests that rely on a blue indicator. That information comes from a prescription medicine used in clinical care; it should not be treated as evidence for unapproved wellness uses.

Why the colour varies from blue to green

Urine is normally yellow because of naturally occurring pigments. When a blue compound is present, the combined colours may appear turquoise, green or blue-green. Appearance can also change with urine concentration, hydration, bathroom lighting and the amount and timing of exposure.

Methylene blue is also metabolised into related compounds, including azure B. The balance between unchanged dye and metabolites, together with ordinary urine pigment, means two people need not see exactly the same shade.

How long does the colour last?

There is no reliable universal number of hours. The medical label reports an approximate 24-hour half-life in humans, but visible colour is not a precise measure of blood concentration and oral products are not equivalent to intravenous treatment. Dose, formulation, hydration and kidney function may all affect what someone observes.

If the colour follows known methylene blue exposure and fades as the compound clears, that is a plausible explanation. Persistent, unexplained or recurrent discolouration deserves professional assessment.

What blue or green urine does not prove

• It does not prove absorption or benefit. A dye can colour urine without demonstrating a desired effect.
• It does not prove purity. Colour cannot identify contaminants, confirm concentration or replace a credible certificate of analysis.
• It is not evidence of “detox”. The simplest explanation is pigment excretion, not removal of unspecified toxins.
• It does not establish the right dose. Darker colour is not a reason to increase or reduce a product without professional guidance.

For a broader evidence overview, read Methylene Blue: Hype, Evidence and Safety. If you are comparing formats, our capsules-versus-liquid guide covers measuring, staining and storage considerations.

When urine colour needs medical attention

Do not assume every blue, green, red or brown change comes from a supplement. Contact a healthcare professional if the colour is unexplained, persists after stopping the suspected source, or occurs with pain, fever, reduced urine, jaundice, marked fatigue, shortness of breath, confusion or other concerning symptoms.

People with G6PD deficiency require particular caution because methylene blue can cause haemolysis. Dark or reddish-brown urine alongside weakness, pallor, jaundice or breathlessness warrants urgent assessment. Serotonin syndrome is a separate emergency risk when methylene blue is combined with serotonergic medicines or certain opioids.

Methylene blue can affect tests and monitoring

Because it is a dye, methylene blue can interfere with some colour-based laboratory tests. The official prescribing information specifically notes possible interference with a urine dipstick test for leucocyte esterase. It can also affect readings from some optical monitoring devices in clinical settings.

Tell the clinician, nurse or laboratory professional about methylene blue before testing. Do not hide supplement use because it feels unrelated—the colour itself may matter to interpretation.

A sensible way to respond

1. Check whether methylene blue is a known ingredient in anything you took.
2. Do not take more simply because you expected to see a stronger colour.
3. Review medicines for interaction risks, especially antidepressants and other serotonergic agents.
4. Keep the original packaging and batch details in case a clinician needs them.
5. Seek advice if the change is unexplained or accompanied by symptoms.

If you are evaluating a product, use our guide on how to choose methylene blue capsules in South Africa. For interaction screening, see methylene blue and antidepressants.

Frequently asked questions

Is green urine after methylene blue normal?

It can occur because blue dye combines visually with the urine’s yellow colour. “Can occur” is not the same as “always harmless”; symptoms and unexplained persistence still matter.

Does blue urine mean methylene blue is working?

No. It shows pigment is present in urine. It does not demonstrate a neurological, energy or other wellness outcome.

Can methylene blue stain the toilet?

Concentrated dye can stain some porous materials. Follow the product’s handling guidance and clean splashes promptly, without mixing household chemicals.

Can other things cause green urine?

Yes. Medicines, dyes, infection and some medical conditions can change urine colour. If methylene blue exposure is uncertain, obtain clinical advice rather than self-diagnosing from colour.

Educational disclaimer: This article is for general education and does not diagnose the cause of urine discolouration. Seek urgent medical care for severe symptoms or a suspected adverse reaction.

Source: FDA prescribing information for ProvayBlue, revised 2023.