Dapsone safety: what to know before and while taking it

Think about dapsone as a useful but demanding medicine. It treats conditions from leprosy to dermatitis herpetiformis and sometimes prevents Pneumocystis infections. But it can cause serious blood problems and allergic reactions. Read this to know the main risks, what tests your doctor should run, and the clear signs that mean you need urgent care.

Key risks and side effects

The biggest safety issues are hemolysis (breaking down red blood cells) and methemoglobinemia (blood can’t carry oxygen well). If you have G6PD deficiency, dapsone can trigger severe hemolysis — that’s why testing G6PD before starting is standard. Other common problems include nausea, headache, and less commonly peripheral neuropathy with long use.

Watch for DRESS (drug reaction with eosinophilia and systemic symptoms) — a serious allergic reaction with fever, widespread rash, swollen lymph nodes, and liver problems. DRESS often appears in the first 4–6 weeks. If you get a high fever plus rash or jaundice, stop dapsone and get medical help immediately.

Some drugs change dapsone levels: rifampin can lower it (may reduce effect), while cimetidine can raise dapsone and increase risk of methemoglobinemia. Combining dapsone with other bone marrow–suppressing medicines (like trimethoprim-sulfamethoxazole) raises the chance of low blood counts.

Practical monitoring and what to do

Before starting: get a CBC (complete blood count), liver tests, and a G6PD screen. Typical dapsone doses: for dermatitis herpetiformis 50–100 mg daily; for leprosy often 100 mg daily as part of combination therapy. Your doctor will adjust based on your condition and response.

Early checks: repeat CBC and liver tests 2–4 weeks after starting. If stable, check every 2–3 months during the first year, then less often if you’re doing well. If you notice fast heart rate, dark urine, pale skin, shortness of breath, or blue lips/fingertips, seek urgent care — these can be signs of hemolysis or methemoglobinemia.

If methemoglobinemia is diagnosed, treatment is often methylene blue IV. Important: methylene blue can’t be used safely in people with G6PD deficiency, so doctors may choose alternatives (ascorbic acid, supportive care, or exchange transfusion) based on the situation. Always tell emergency staff about G6PD status.

Pregnancy and breastfeeding: dapsone crosses the placenta and enters breast milk. It’s sometimes used in pregnancy when benefits outweigh risks, but this needs close medical oversight. Don’t start or stop dapsone on your own — talk with your prescriber about safer options if you’re pregnant or breastfeeding.

Bottom line: dapsone works, but it needs respect. Get G6PD tested, stick to the lab schedule, watch for specific symptoms, and report other medicines you take. That keeps treatment effective and lowers risk.