Common side effects of methylene blue

Common Side Effects of Methylene Blue

Methylene blue is generally well-tolerated at therapeutic doses, but it can cause a range of side effects. These can be grouped into common, less common, and serious adverse effects.

Common Side Effects

• Blue or green discoloration of urine and skin (very common and harmless)

• Nausea, vomiting, and diarrhea

• Abdominal pain or stomach upset

• Changes in taste (dysgeusia) or loss of taste

• Increased sweating

• Feeling hot or cold

• Muscle or joint pain

• Pain or discomfort at the infusion site

• Headache

• Dizziness or lightheadedness

• Skin discoloration (blue or bluish patches)

Less Common Side Effects

• Back pain, muscle spasms, chills

• Runny nose, sore throat

• General feeling of discomfort or illness

• Trouble sleeping

Serious Side Effects (Require Immediate Medical Attention)

• Agitation, confusion, or restlessness

• Chest tightness, chest pain, or rapid heartbeat

• Difficulty breathing or swallowing

• Bluish-colored lips, fingernails, or palms (cyanosis)

• Unusual tiredness or weakness

• Fever

• Hives, rash, or severe allergic reactions (anaphylaxis)

• Unusual bleeding or bruising

• Seizures

• Hemolytic anemia (especially in people with G6PD deficiency)

• Serotonin syndrome (especially when combined with serotonergic medications such as SSRIs, SNRIs, or MAOIs; symptoms include muscle spasms, sweating, agitation, tremor, and confusion)

Other Notable Effects

• Dark urine (harmless and expected)

• Injection site reactions (pain, swelling, redness)

• Pale skin

Summary:

The most common side effects are blue/green discoloration of urine and skin, gastrointestinal upset (nausea, vomiting, diarrhea), headache, and dizziness. Serious reactions such as serotonin syndrome, hemolytic anemia (in G6PD deficiency), allergic reactions, and cardiac issues are rare but require immediate medical attention.