Levamisole side effects — common problems and the rare but serious risks

A small amount of levamisole can cause a dramatic drop in white blood cells in some people. That’s the single fact that makes this drug worth respecting. Whether levamisole was prescribed years ago as an anti-parasite or you suspect exposure through contaminated cocaine, you should know the typical reactions and the warning signs that need urgent care.

Common side effects

Most people who take levamisole experience mild, short-lived symptoms. These include nausea, vomiting, diarrhea, stomach cramps, headache, dizziness, and tiredness. Skin rashes and mild itching also happen. These issues usually show up within hours to a few days and fade if the drug is stopped.

Some people notice temporary changes in taste or muscle aches. If your symptoms are only mild stomach upset or a small rash, call your prescriber for advice — they may tell you to stop the medicine or to watch closely at home.

Serious risks and what to do

The two most dangerous problems linked to levamisole are agranulocytosis (very low white blood cell counts) and vasculitis (inflammation of small blood vessels). Agranulocytosis makes you prone to severe infections. Watch for fever, sore throat, mouth ulcers, swollen glands, unexplained bruises, or wounds that won’t heal. These can appear days to weeks after exposure.

Vasculitis from levamisole often causes purple or black patches on the skin, especially on the ears, nose, hands, and feet. Lesions can look like purpura, blisters, or areas of skin death. If you see these changes, get urgent medical attention.

If you or someone else is showing fever plus sore throat, mouth sores, new skin bruises, or spreading skin lesions, stop the drug (if known) and seek emergency care. Tell clinicians you may have taken levamisole — or, if relevant, that you used cocaine that might have been cut with levamisole. Hospitals usually check a complete blood count (CBC) with differential right away. Treatment may include stopping the drug, antibiotics if there’s infection, and hospital care for very low white cells.

Timing matters: agranulocytosis often shows up 1–3 weeks after exposure, but it can be sooner. Don’t ignore fever or a sore throat even if the rest of you feels fine.

If levamisole is prescribed by your doctor, they should monitor your blood regularly. Tell your provider about any other medicines or immune conditions you have — combining drugs that suppress the immune system increases risk. If you use illicit drugs, avoid them and seek help; if you develop symptoms, be honest with clinicians so they can test and treat correctly.

Bottom line: mild GI or headache side effects are common and often pass. But fever, sore throat, mouth ulcers, unexplained bruising, or purple skin lesions need immediate attention. Quick testing (CBC) and stopping the drug can prevent serious complications.