Methylene blue, also known as methylthioninium chloride, is a compound with a dark blue-green color. The chemist and textile manufacturer, Heinrich Caro, initially synthesized the substance as a clothing dye in 1876.

Later, scientists started exploring its potential clinical uses. They discovered that methylene blue has various properties and mechanisms of action that could influence biological functions in the body.

Despite the potential benefits of methylene blue, the medication can cause side effects that may be severe. These include serotonin syndrome in people taking certain medications and various central nervous system symptoms.

In 2016, the FDA approved methylene blue as a treatment for methemoglobinemia. However, the FDA has not officially approved various off-label uses of the medication. “Off-label” means doctors may sometimes prescribe the medication to treat conditions besides methemoglobinemia if they feel it will be safe and beneficial for their patients.

Researchers are also exploring several promising potential uses of methylene blue that scientists may be able to develop in the future.

The FDA has currently only approved methylene blue to treat methemoglobinemia.

Methemoglobinemia affects the structure of iron molecules in the blood, preventing oxygen from binding to them. As a result, the blood cannot transport enough oxygen throughout the body, which may lead to severe and life-threatening complications.

Off-label methylene blue uses include:

• Diagnostic mapping: Health professionals may use methylene blue as a dye to help identify and map out lymph nodes and other specific areas during imaging procedures.
• Malaria: Methylene blue may help kill malaria parasites that are resistant to other treatments.
• Vasoplegic syndrome: Vasoplegic syndrome is a rare occurrence in which the blood vessels widen uncontrollably during cardiac surgery, causing a severe drop in blood pressure. Methylene blue may help treat the condition.
• Ifosfamide-induced encephalopathy: Ifosfamide is a chemotherapy drug that doctors use to treat various types of cancer. The drug may cause encephalopathy in 10% to 30% of people, which is a buildup of toxins that can result in brain damage and death. Research suggests that methylene blue may be an effective treatment.

Researchers are investigating the potential of methylene blue as a treatment for Alzheimer’s disease and other neurodegenerative conditions. The medication may inhibit the buildup of an abnormal protein in the brain called tau that may contribute to cognitive decline.

More research is necessary to determine how safe and effective these emerging uses of methylene blue may be.

Research is ongoing into other potential benefits of methylene blue, including:

Researchers believe the antioxidative properties of methylene blue could help reduce the oxidative stress involved in aging and cell damage.

Antioxidants fight unstable molecules called free radicals in the body that can lead to oxidative damage. As a person ages, the accumulation of oxidative damage to their DNA, proteins, and lipids may affect how their cells work.

Researchers believe it may be possible to use methylene blue to help prevent some of the oxidative damage involved in aging, which could help treat age-related conditions like memory loss, neurodegeneration, and skin aging.

However, more large-scale clinical research in humans is necessary to determine whether methylene blue has significant benefits in supporting aging.

Methylene blue may relieve pain in the following ways:

• Anti-inflammation: The medication may trigger various anti-inflammatory pathways and decrease the expression of pro-inflammatory proteins called cytokines. The decrease in inflammation may reduce pain.
• Sodium current reduction: Sodium currents refer to the flow of sodium molecules through channels in cells. The channels transmit pain signals to the brain. Methylene blue may help reduce sodium current activity and alleviate pain.
• Denervation: Methylene blue may help destroy nerve endings in the skin, blocking them from sending pain signals.

Although methylene blue has potential benefits as a pain-reliever, it may lead to serious side effects at certain doses. These include serotonin toxicity, or serotonin syndrome, a potentially life threatening condition. Research also suggests that methylene blue can damage brain cells.

More research into methylene blue’s pain relieving effects in humans is necessary.

Research suggests that combining methylene blue with a type of cancer treatment called photodynamic therapy could have anticancer benefits.

Photodynamic therapy uses a light-activated drug to destroy cancer cells. A 2023 review of human and animal studies suggests that photodynamic therapy with methylene blue may be effective against various types of cancer, including carcinoma, melanoma, and colorectal cancer.

More research is necessary to determine how safe and effective methylene blue may be as a cancer treatment.

A person should use methylene blue according to a doctor’s instructions, or under the supervision of a healthcare professional. There are potential side effects and a risk of health complications.

To treat methemoglobinemia, a healthcare professional will typically administer a 1% solution of methylene blue intravenously (through a vein) at a dose of 1 milligram (mg) per kilogram (kg) of a person’s body weight.

If people choose to take methylene blue supplements, they must choose a pharmaceutical-grade product, which will have “USP” on the label. Follow the dosage instructions on the package label.

The medication may cause adverse effects, which can include:

• discolored urine
• limb pain
• serotonin syndrome
• tremors
• confusion
• dizziness
• headaches

Methylene blue may cause the following serious health complications in babies:

Experts advise that a person should not take methylene blue if they:

• have had hypersensitivities or allergic reactions to the medication in the past
• are pregnant, as the medication may result in fetal death
• have a glucose-6-phosphate dehydrogenase deficiency

Methylene blue may increase the risk of serotonin syndrome for people who take medications that affect serotonin. These include the following types of antidepressants:

Methylene blue is available without a prescription, sometimes in the form of oral supplements. It is important to note that the FDA does not regulate the safety or efficacy of supplements in the same way as medications.

Intravenous methylene blue to treat methemoglobinemia requires a prescription and should be administered by a healthcare professional.

A doctor may safely prescribe other forms of methylene blue for off-label uses.

Methylene blue can cause serious, sometimes life threatening, complications. A person should check with a doctor before starting any new medications or supplements and follow the doctor’s instructions.

Methylene blue is a medication that the FDA has approved to treat methemoglobinemia, a blood disorder that affects the blood’s ability to transport oxygen.

A doctor may sometimes use or prescribe the medication off-label to treat certain conditions, including vasoplegic syndrome and malaria.

Researchers are studying methylene blue as a potential treatment for various health conditions, including certain cancers and Alzheimer’s disease.

There are potential benefits and risks of methylene blue. A person should speak with a doctor about whether the medication is safe for them.