Internet is full of praise to a liquid chemical called methylene blue, which is sold as a health supplement.
In the last five or ten years, methylene blue was promoted online as an alleged nootropic agent, a substance that improves cognitive function. Sellers claim that brain energy increases, improves memory, concentration and dissipates mental confusion, among other supposed benefits.
Health influencers, such as Podcaster Joe Rogan, is among those who praise him. In February 2025, shortly before being confirmed as Secretary of Health and Human Services, Robert F. Kennedy Jr. appeared in a video pouring into a glass a blue liquid that is very presumed that it is methylene blue, although it never promoted it verbally.
As a researcher specialized in inflammation and cancer, I investigate how dyes affect human health. The statements about methylene blue are attractive, and it is easy to believe in their promise. However, so far, the evidence that supports its health benefits is scarce, and there are serious risks when using this substance outside of medical practice.
What is methylene blue?
Methylene blue is a synthetic dye that is presented in the form of dark green powder and acquires an intense blue color when dissolving in water. My work and that of others suggest that many synthetic dyes widely used in food and medications can trigger potentially harmful reactions in the immune system.
However, unlike food dyes of common use – one of which was recently prohibited by the Food and EU medications administration – methylene blue is not derived from oil, also known as crude oil. On the other hand, it comes from a different family of dyes, which is not considered to present these health risks.
Methylene blue was synthesized for the first time in 1876 as a dye for textiles and was valued by its intense color and its ability to adhere well to fabrics. Shortly after, the German doctor Paul Ehrlich discovered his ability to dye biological tissues and eliminate the parasite that causes malaria, which made him one of the first synthetic drugs used in medicine.
The chemist was not generalized as a treatment against malaria because it was not more effective than quinine, standard treatment at that time. But in the 1930s, the dye found a new use to prove the safety of raw milk or without pasteurizing. If its blue color faded quickly, the milk was contaminated with bacteria, but if it remained blue, it was considered relatively clean.
This security test is now practically obsolete. But it works thanks to the chemical superpower of methylene blue: its molecules can exchange electrons with other molecules, such as a small battery charger.
How do doctors use today?
This same chemical superpower allows some of the medical uses of methylene blue. The most significant is that doctors use it to treat an unusual blood disorder called methemoglobinemia, in which hemoglobin, a protein rich in iron from red blood cells that transports oxygen, adopts a different form that cannot perform its function. Methylene blue restores the function of hemoglobin by transferring an electron.
Doctors also usually use methylene blue to treat the effects of carbon monoxide poisoning, septic clash or drug toxicity such as chemotherapy. It is also used as a surgical dye to highlight specific tissues, such as lymph nodes, or to identify where the tissue has leaks and, therefore, can be damaged.
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How does it affect the brain?
Methylene blue can enter the brain through the protective barrier of the surrounding tissue. The researchers also discovered that this chemical can protect and strengthen mitochondria, cellular structures that are often described as cell power plants. Methylene blue can help mitochondria to generate energy so that cells use it. For these reasons, researchers are studying the effect of methylene blue on the brain.
Until now, most of what is known about the effects of this substance on the brain comes from studies in rats and cells cultivated in laboratory plates, not in people. For example, researchers have discovered that methylene blue can improve learning, enhance memory and protect rats brain cells with a condition similar to Alzheimer’s disease.
Studies in rodents also discovered that methylene blue can protect the brain from the damage caused by a brain injury. Other studies showed that methylene blue is useful in the treatment of ischemic stroke in rats. However, to date, no investigation examined whether the brain from traumatic brain lesions or strokes protects.
Some clinical trials have investigated the effects of methylene blue in the treatment of aspects of Alzheimer’s disease in people, but a review of these tests carried out in 2023 indicates that their results have been mixed and not conclusive. A small study of 26 people discovered that a single low dose of the chemical improved memory by approximately 7 % and increased brain activity during thought tasks. Another study by the same researchers discovered that methylene blue modified the connection between different parts of the brain, although it did not improve thought skills.
Although some studies in people have shown indications that methylene blue could be beneficial for some problems related to the brain, such as pain management and neuropsychiatric disorders, to date, these studies have been small. This suggests that, although there may be circumstances in which methylene blue is beneficial for the patient, researchers have not yet determined what they are.
Is it safe?
Methylene blue is generally safe when used under medical supervision. However, this chemical presents some serious risks.
On the one hand, you can interact with common use medications. Methylene blue inhibits a molecule called monoamineoxidase, whose function is to decompose an important chemical of the brain, serotonin. Many medications of common use to treat anxiety and depression act on serotonin.
Taking the supplement together with these medications can cause a condition called serotonergic syndrome, which can cause agitation, confusion, high fever, accelerated heart rate, muscle stiffness and, in severe cases, seizures or even death.
In people with a rare genetic deficiency of an enzyme called G6PD, methylene blue can cause a dangerous condition in which red blood cells break too fast. In high doses, the chemical can also raise blood pressure or cause heart problems. In addition, it is considered insecure for pregnant or breastfeeding women because it can damage the fetus or the baby.
In general, although scientists have found indications of some fascinating properties of methylene blue, much larger and longer tests are needed to know if it really works, what is the right dose and how sure it is over time.
*Lorne J. Hofseth He is an associate professor and dean of research at the Faculty of Pharmacy of the University of South Carolina.
This note was originally posted in The Conversation
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