Does Methylene Blue Cure Cancer?

Methylene blue is a deep blue dye. In the last few years it has become a wellness trend. Videos show people dropping it into water and turning their tongues blue. The promises attached to it are broad: more energy, sharper thinking, a longer life. In some posts the claim goes further and says it prevents or cures cancer.

The claim we are checking here is the specific one: that taking methylene blue prevents or cures cancer.

Verdict: not proven. There is no approved methylene blue product for treating or preventing any cancer, and no reliable evidence that swallowing it does so.

Methylene blue is a prescription drug in the United States. The FDA-approved product is ProvayBlue, a methylene blue injection from Provepharm SAS under new drug application 204630. FDA approved it on April 8, 2016, with orphan status, meaning it treats a rare condition. It comes in two vial sizes, both at the same strength. It is given into a vein.

This is a hospital injection with a strength printed on the vial. It is not a supplement you dose yourself.

Labels for methylene blue injection, such as the one on DailyMed, give one use. It is indicated for the treatment of pediatric and adult patients with acquired methemoglobinemia.

Methemoglobinemia is a blood problem, not a cancer. The label gives a weight-based dose given into a vein by clinicians. It says not to give the injection under the skin. Nothing on the label mentions cancer.

Methylene blue injection carries a boxed warning, the most serious warning FDA uses. It says the drug "may cause serious or fatal serotonergic syndrome" when combined with serotonergic drugs and opioids. The label says to avoid using it with:

• Selective serotonin reuptake inhibitors (SSRIs), a common antidepressant class.
• Serotonin and norepinephrine reuptake inhibitors (SNRIs), another antidepressant class.
• Monoamine oxidase inhibitors (MAOIs).
• Opioids.

The label lists these signs of serotonin syndrome: agitation, hallucinations, delirium, coma, fast heartbeat, and unstable blood pressure. It also lists dizziness, sweating, flushing, high body temperature, tremor, rigid muscles, seizures, and nausea, vomiting or diarrhea.

Antidepressants and opioids are both used in cancer care. Someone self-dosing a blue liquid from the internet could be taking one of these without connecting it.

• Call 911 or go to the nearest emergency department if someone who took methylene blue has confusion, seizures, or hallucinations. Also go for a very high temperature, rigid muscles, or if they are hard to wake.

The label lists two contraindications, meaning reasons not to use it:

• Severe hypersensitivity to methylene blue.
• Glucose-6-phosphate dehydrogenase deficiency, known as G6PD deficiency, because of the risk of hemolytic anemia.

The label also says methylene blue interferes with pulse oximeter readings, the clip-on devices that read oxygen levels through the skin. It causes blue discoloration of skin and body fluids.

Methylene blue does appear in cancer research. It is worth understanding what it is doing there.

A search of the federal trials registry (ClinicalTrials.gov) for methylene blue in cancer returns studies on staining and mapping. Examples include sentinel node biopsy in endometrial cancer and methylene blue staining during endoscopy in Barrett's esophagus. In these studies the dye marks tissue so a surgeon or endoscopist can find it.

That is a different job from treating cancer. None of this shows that swallowing methylene blue treats cancer.

FDA maintains a consumer page on this exact pattern. Its title is "Products Claiming to 'Cure' Cancer Are a Cruel Deception."

Two points from it are worth carrying:

• Drugs and devices intended to treat cancer must gain FDA approval or clearance before they are marketed and sold. The review process is what establishes that a product is safe and effective for its stated use.
• Fraudulent cancer products are often advertised as "natural" and falsely labeled as dietary supplements. FDA warns they may cause harm by delaying or interfering with proven treatment, and that without review they may contain dangerous ingredients.

FDA also lists the red flags that mark this kind of marketing: "miracle cure," "works in minutes," "guaranteed." When FDA finds such claims it sends warning letters and can take further legal action.

The FDA says it does not approve dietary supplements before they are marketed and does not test them before they are sold.

Tell your oncology team before taking anything, and bring the actual bottle. The interaction list above is the reason. A pharmacist can check it against every drug you are on.

If a product promises a cure, treat the promise itself as the warning sign rather than the ingredient. Our page on whether supplements can cure cancer covers the pattern across products. Our claim checks on baking soda and turmeric also show how a real laboratory finding gets stretched into a cure story.

• DailyMed: methylene blue injection label.
• Drugs@FDA: ProvayBlue, NDA 204630.
• FDA: products claiming to cure cancer.
• FDA: questions and answers on dietary supplements.
• ClinicalTrials.gov API: methylene blue studies in cancer.