Levamisole, sold under the brand name Ergamisol among others, is a medication used to treat parasitic worm infections, specifically ascariasis and hookworm infections. It is taken by mouth. Side effects may include abdominal pain, vomiting, headache, and dizziness. Use is not recommended during breastfeeding or the third trimester of pregnancy. Serious side effects may include an increased risk of infection. It belongs to the anthelmintic class of medications. Levamisole was invented in 1966 in Belgium by Janssen Pharmaceuticals. It is on the World Health Organization's List of Essential Medicines. Levamisole is also used as a dewormer for cattle. It is also often used as a cutting agent in illegal cocaine. In February 2026, the Pharmacovigilance Risk Assessment Committee of the European Medicines Agency recommended that medicines containing levamisole be withdrawn from the EU market. This follows an EU-wide review which concluded that the benefits of these medicines no longer outweigh their risks for the treatment of parasitic worm infections in adults and children.
Medical uses
Worms Levamisole was originally used as an anthelmintic to treat worm infestations in both humans and animals. Levamisole works as a nicotinic acetylcholine receptor agonist that causes continued stimulation of the parasitic worm muscles, leading to paralysis. Levamisole has gained prominence among aquarists as an effective treatment for Camallanus roundworm infestations in freshwater tropical fish. Levamisole has been used to treat small ruminant animals since the late 1960s. Levamisole-resistant parasitic worms are common in sheep farms in New Zealand, Uruguay, Paraguay, and Brazil.
Other Levamisole has been used to treat a variety of dermatologic conditions, including skin infections, leprosy, warts, lichen planus, and aphthous ulcers. An interesting side effect these reviewers reported in passing was "neurologic excitement". Later papers, from the Janssen group and others, indicate levamisole and its enantiomer, dexamisole, have some mood-elevating or antidepressant properties, although this was never a marketed use of the drug.
Adverse effects One of the more serious side effects of levamisole is agranulocytosis, or the depletion of the white blood cells. In particular, neutrophils appear to be affected the most. This occurs in 0.08–5% of the studied populations. It has been used as an adulterant in cocaine, resulting in serious side effects that present as levamisole induced necrosis syndrome, in which erythematous painful papules can appear almost anywhere on skin. In September 2025, the Pharmacovigilance Risk Assessment Committee (PRAC) of the European Medicines Agency started a review of medicines containing levamisole, authorized in four countries of the European Union to treat infections caused by parasitic worms in adults and children. The review follows concerns about a risk of leukoencephalopathy with levamisole, a potentially serious condition that damages the white matter of the brain. White matter is made of nerve fibres covered by a protective layer called myelin, which allows efficient communication between different parts of the brain. Leukoencephalopathy can be life-threatening and debilitating, especially when left undiagnosed or untreated. It may lead to a range of neurological symptoms, including but not limited to, confusion, weakness or impaired muscle function, difficulties with movement coordination, and impaired or lost speech or vision. Leukoencephalopathy has already been identified as a potential risk with levamisole, and the product information of levamisole medicines include the general term encephalopathy (a group of brain dysfunction conditions). In February 2026, the PRAC recommended that medicines containing levamisole be withdrawn from the EU market. This follows an EU-wide review which concluded that the benefits of these medicines no longer outweigh their risks for the treatment of parasitic worm infections in adults and children.
Metabolism Levamisole is readily absorbed from the gastrointestinal tract and metabolized in the liver. Its time to peak plasma concentration is 1.5–2 hours. The plasma elimination half-life is fairly quick at 3–4 hours which can contribute to not detecting levamisole intoxication. The metabolite half-life is 16 hours. Levamisole's excretion is primarily through the kidneys, with about 70% being excreted over 3 days. Only about 5% is excreted as unchanged levamisole. Drug testing of racehorse urine has led to the revelation that among levamisole equine metabolites are both pemoline and aminorex, stimulants that are forbidden by racing authorities. Further testing confirmed aminorex in human and canine urine, meaning that both humans and dogs also metabolize levamisole into aminorex, though it is unclear whether plasma aminorex is present at any appreciable level. Blood samples following oral administration of levamisole out to 172 hr post-dose did not demonstrate any plasma aminorex levels above that of the limit of quantification (LoQ). Additionally, in cocaine-positive plasma samples, of which 42% contained levamisole, aminorex was never reported at concentrations higher than LoQ.
Detection in body fluids Levamisole may be quantified in blood, plasma, or urine as a diagnostic tool in clinical poisoning situations or to aid in the medicolegal investigation of suspicious deaths involving adulterated street drugs. About 3% of an oral dose is eliminated unchanged in the 24-hour urine of humans. A post mortem blood levamisole concentration of 2.2 mg/L was present in a woman who died of a cocaine overdose.
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