Methylene Blue: What the research Says, and Why the MHRA Warns About Antidepressants

What is methylene blue?

Methylene blue (methylthioninium chloride) is a blue dye first made in the 1870s. In the UK it is a licensed medicine, given by slow injection to treat drug-induced methaemoglobinaemia, a condition where the blood cannot carry oxygen properly. It is also used as a surgical dye and in some urinary products abroad.

Since around 2023 it has been promoted on social media as a "nootropic" (a brain-boosting substance) and longevity tool, often as drops added to water.

Why is methylene blue popular now?

Methylene blue spread through longevity podcasts and short videos from around 2023, often shown as a few drops turning a glass of water bright blue. Its appeal is easy to see: it is old, cheap, has a real medical history, and its lab effects on mitochondria sound like a direct route to "more energy". Some sellers describe it as "pharmaceutical grade" or "USP grade", which sounds reassuring but says nothing about whether it is appropriate to take at home.

Google's shopping results in the UK mix these human-use drops with aquarium treatments and laboratory stains, which shows how blurred the market is.

Is methylene blue legal to buy in the UK?

Methylthioninium chloride is a licensed medicine in the UK for a specific hospital use, and the MHRA's safety update relates to that licensed product. Drops and capsules sold online for brain health are not licensed for those uses, so they have not been assessed by the MHRA for quality, dose or benefit. If a product makes medicinal claims (for example treating depression or memory loss), it is being presented as a medicine without a licence.

What does it claim to do?

Supporters say methylene blue:

• boosts energy by helping mitochondria (the energy-producing parts of cells) work better
• sharpens memory and focus
• lifts mood and helps depression
• protects the brain against ageing and dementia
• acts as an antioxidant and slows ageing

The mitochondria idea has a real basis: in the lab, methylene blue can pass electrons along the chain that cells use to make energy. The question is whether that translates into benefits for healthy people taking it at home.

What does the evidence show?

Memory and focus

The study most often quoted is a 2016 randomised trial in 26 healthy adults aged 22 to 62. One hour after a single low dose, brain scans showed more activity during attention and memory tasks, and correct answers on a memory test rose by 7% compared with placebo. It was carefully done but tiny and measured only one dose. Harvard Health notes that a 2023 study at similar doses found an 8% drop in brain blood flow, so even the short-term picture is unclear.

Mood

A 2017 crossover trial in 37 people with bipolar disorder found methylene blue added to their usual treatment improved residual depression and anxiety. This was in a specialist setting with careful medicine checks, which matters given the interaction risk below.

Dementia

A methylene blue derivative called LMTM was tested in a phase 3 trial in mild to moderate Alzheimer's disease. The main analysis was negative: it did not show benefit as an add-on treatment. The trial was funded by the drug's developer.

Energy and longevity

We found no human trials showing methylene blue improves energy, fitness, healthspan or lifespan in healthy people. Claims rest on lab and animal work.

Who should be careful?

This is the most important section of this page.

People taking antidepressants or other serotonergic drugs. Methylene blue is a potent inhibitor of MAO-A, the enzyme that breaks down serotonin. The MHRA warned that high IV doses should be avoided in people on serotonergic antidepressants such as SSRIs, clomipramine and venlafaxine because of central nervous system toxicity, with features including confusion, agitation, altered muscle tone and reduced consciousness. The UK product information extends the warning to SNRIs, MAOIs and opioids. A systematic review found the reactions were consistent with serotonin syndrome, and a 2018 case report and review described serotonin syndrome after oral, not just injected, methylene blue. Serotonin syndrome can be fatal.

Common serotonergic medicines include sertraline, citalopram, fluoxetine, venlafaxine, duloxetine, amitriptyline, tramadol and some migraine and cough medicines. If you take any regular medicine, speak to a pharmacist before using methylene blue.

People with G6PD deficiency. The UK SmPC lists glucose-6-phosphate dehydrogenase deficiency as a contraindication because of the risk of haemolytic anaemia (red blood cells breaking down). Many people with G6PD deficiency do not know they have it.

Pregnant and breastfeeding women. The SmPC says it should not be used in pregnancy unless clearly necessary, as animal studies showed reproductive toxicity.

Anyone buying online. "USP" or "pharmaceutical grade" describes purity, not safety for self-treatment. Aquarium and laboratory dyes are not made for people and may contain impurities.

If you are still considering it: what to know

We do not recommend self-treatment with methylene blue and feature no products. If you are curious:

• Speak to your GP or pharmacist first, and bring a full list of your medicines and supplements, including St John's wort.
• Ask whether you should be tested for G6PD deficiency.
• Expect blue-green urine; this is harmless but can mask other changes.
• Be sceptical of any seller making claims about energy, anti-ageing or "mitochondrial support". None are backed by human trials.

Bottom line

Methylene blue is a genuine medicine with a narrow, proven hospital use. Its wellness reputation rests on one small single-dose memory study, a supervised psychiatric trial and laboratory work. Against that sits a clear regulatory warning about serotonin toxicity with very common antidepressants and a contraindication in G6PD deficiency. For energy, focus and healthy ageing, sleep, exercise and treating any underlying condition remain far better supported.