Levamisole is a veterinary deworming drug that has become one of the most common and harmful adulterants in the illicit cocaine supply. Originally developed in the 1960s as a treatment for parasitic worms in livestock, it was briefly used in human medicine before the U.S. Food and Drug Administration pulled its approval in 2000 because of serious side effects, particularly a tendency to wipe out white blood cells. Despite that withdrawal, levamisole remains cheap, widely available in veterinary channels, and physically similar enough to cocaine powder that it has become a go-to cutting agent for drug traffickers around the world. The consequences for people who unknowingly consume it range from immune system collapse to disfiguring skin death to brain damage.
From Livestock Dewormer to Cancer Drug and Back
Levamisole was first synthesized in the early 1960s as an anthelmintic, a drug that kills parasitic worms. It works by mimicking the neurotransmitter acetylcholine at receptors on worm muscle cells, forcing the muscles into sustained contraction and paralyzing the parasite so the host animal can expel it.1Pesticide Science. Mode of action of the anthelmintics morantel, pyrantel and levamisole on muscle cell membrane of the nematode Ascaris suum It became a staple in veterinary medicine for cattle, sheep, pigs, and poultry, and it is still used that way today in many countries.
Researchers soon noticed something unexpected: levamisole also seemed to boost the immune system in treated animals and, eventually, in humans. Through the 1970s and 1980s it gained recognition as an “immunotropic” agent, meaning it could modulate immune responses. That property led to its most prominent human use. In the late 1980s, clinical trials showed that levamisole, combined with the chemotherapy drug fluorouracil, improved survival in patients with operable colon cancer.2International Journal of Immunopharmacology. Levamisole, the story and the lessons For roughly a decade it was a standard part of colon cancer treatment in the United States. But as data accumulated on its side effects and better alternatives emerged, the FDA revoked approval for human use in 2000.3Therapeutic Drug Monitoring. Levamisole—a Toxic Adulterant in Illicit Drug Preparations: a Review It remains available for human use in some countries outside the United States, and its veterinary formulations are sold globally.
How It Ended Up in the Cocaine Supply
At some point in the mid-2000s, levamisole began appearing as an adulterant in seized cocaine samples at alarming rates. By the time public health agencies took notice, it was already widespread. Several properties make it attractive to traffickers. It is an odorless white powder with a “fish-scale” sheen that closely resembles high-quality powder cocaine, making it hard for buyers to detect visually.4PubMed Central. Levamisole: A High Performance Cutting Agent It is cheap and easy to obtain through veterinary supply chains.5PubMed. Levamisole in Illicit Trafficking Cocaine Seized: A One-Year Study
But the story is more interesting than simple economics. Animal research suggests levamisole actually enhances the effects of cocaine. It can boost both the rewarding and stimulant properties of low cocaine doses in rats, while also having modest stimulant activity on its own.6PubMed Central. Levamisole enhances the rewarding and locomotor-activating effects of cocaine in rats The mechanisms behind this synergy appear to involve several pathways: levamisole inhibits an enzyme that breaks down dopamine and other mood-related brain chemicals, it activates nicotinic receptors in the brain, and it raises levels of the body’s natural opioid-like compounds.7PubMed Central. Levamisole and cocaine synergism: a prevalent adulterant enhances cocaine’s action in vivo In other words, levamisole is not just filler. It is a pharmacologically active adulterant that can make a weaker batch of cocaine feel stronger. Whether traffickers figured this out deliberately or stumbled onto it remains unclear, but the result is the same: consumers get a product that feels potent while containing less actual cocaine, and they absorb a drug that can devastate their immune system.
What Levamisole Does to the Immune System
The same immune-modulating properties that once made levamisole useful in cancer therapy are precisely what make it dangerous when consumed repeatedly and without medical supervision. In controlled settings, levamisole ramps up certain immune-cell activities. It increases the maturation of dendritic cells, which are specialized immune cells that activate the broader immune response, and it promotes the production of signaling molecules that steer the immune system toward a particular mode of attack.8PubMed Central. Levamisole enhances immune response by affecting the activation and maturation of human monocyte-derived dendritic cells It also increases certain surface markers on dendritic cells that help stimulate a class of immune cells involved in fighting infections.9PubMed Central. The potential immunomodulatory effect of levamisole in humans and farm animals
The problem is that this immune stimulation is not always targeted. In some people, levamisole triggers the production of antibodies that attack the body’s own neutrophils, the white blood cells that serve as the immune system’s first responders against bacterial infections. Studies of patients who developed dangerously low neutrophil counts while taking levamisole found that all of them had developed an IgM-class antibody that reacted against neutrophils from unrelated donors, not just their own.10Blood. Studies on Levamisole—Induced Agranulocytosis This condition, called agranulocytosis, leaves a person essentially defenseless against bacterial infections. A sore throat or minor wound can become life-threatening.
Levamisole also pushes neutrophils to form what are called neutrophil extracellular traps, web-like structures that neutrophils release to ensnare pathogens. Normally this is a useful defense mechanism, but levamisole causes excessive and inappropriate trap formation, which damages blood vessel walls and fuels autoimmune inflammation.11PubMed Central. A role for muscarinic receptors in neutrophil extracellular trap formation and levamisole-induced autoimmunity The combination of losing neutrophils to antibody destruction while also having the remaining neutrophils cause vascular damage creates a particularly nasty double hit.
Skin Necrosis and Vasculitis
The most visually striking consequence of levamisole exposure is purpuric skin damage, a pattern of dark purple or black lesions that often appears on the earlobes, nose, cheeks, and extremities. The distribution is distinctive enough that emergency physicians who have seen it before can sometimes suspect levamisole involvement on sight. A typical case involves purpuric and necrotic lesions on the nose, cheeks, and ears, accompanied by low white blood cell and platelet counts, along with positive tests for anti-neutrophil cytoplasmic antibodies.12PubMed Central. Levamisole-adulterated cocaine induced skin necrosis of nose, ears, and extremities: Case report Earlobes are so commonly affected that earlobe necrosis in a cocaine user has become almost a clinical calling card for this condition.13PubMed Central. Levamisole-contaminated cocaine: an emergent cause of vasculitis and skin necrosis
Under the microscope, the affected skin shows a mix of small-vessel inflammation and blood clotting within tiny vessels, with deposition of complement proteins that indicate the immune system is attacking the vessel walls.14PubMed. Cocaine-related retiform purpura: evidence to incriminate the adulterant, levamisole Additional research has found that levamisole likely works together with cocaine’s own metabolic products to amplify this microvascular injury, involving complement-mediated damage, programmed cell death in blood vessel walls, and elevated expression of adhesion molecules that attract inflammatory cells to the vessel lining.15The American Journal of Dermatopathology. Cocaine-Associated Retiform Purpura: A C5b-9–Mediated Microangiopathy Syndrome Associated With Enhanced Apoptosis and High Levels of Intercellular Adhesion Molecule-1 Expression The result is tissue death that can require surgical removal of affected skin, and in severe cases the damage is permanent and disfiguring.
Neurological Damage
Beyond the skin and the blood, levamisole can attack the brain. A condition called multifocal inflammatory leukoencephalopathy, which involves inflammation and damage to the brain’s white matter, has been linked to levamisole-adulterated cocaine. In one reported case, a 29-year-old man experienced two separate episodes of severe neurological symptoms with widespread white-matter lesions in the brainstem and cerebellum after sporadic cocaine use. A urine test confirmed levamisole exposure. His deficits improved after stopping cocaine and receiving high-dose steroid treatment, but the authors emphasized that early diagnosis was critical for recovery.16PubMed Central. Multifocal leukoencephalopathy associated with intensive use of cocaine and the adulterant levamisole in a 29-year old patient
Not all cases resolve so well. A fatal case has been documented in which levamisole-associated leukoencephalopathy caused irreversible neurological damage, leading to the patient’s death.17PubMed. Fatal levamisole-associated multifocal inflammatory leukoencephalopathy following levamisole-adulterated cocaine use The range of outcomes, from full recovery with prompt steroid treatment to death, underscores both the seriousness of the condition and the importance of clinicians thinking of levamisole when a cocaine user presents with unexplained neurological decline.
A Diagnosis That Fools Doctors
One of levamisole’s most dangerous properties is that the autoimmune response it triggers looks, on standard lab tests, almost identical to genuine autoimmune diseases like granulomatosis with polyangiitis (formerly called Wegener’s) or lupus. The vast majority of affected patients test positive for p-ANCA antibodies, and many are also positive for additional autoantibodies including anti-double-stranded DNA, antinuclear antibodies, and anti-cardiolipin antibodies.18PubMed Central. Levamisole adulterated cocaine associated ANCA vasculitis: review of literature and update on pathogenesis A characteristic feature is dual positivity for both PR3 and MPO ANCA, a pattern that is unusual in primary autoimmune vasculitis but common in drug-induced forms.
This laboratory resemblance has real consequences. In one case series, five of six patients admitted with purpuric lesions and vasculitis were initially diagnosed with and treated for autoimmune conditions before their actual diagnosis of levamisole-induced vasculopathy was recognized.19PubMed. Levamisole toxicity mimicking autoimmune disease Misdiagnosis matters because the treatment paths diverge sharply. A patient with primary autoimmune vasculitis would be started on long-term immunosuppressive therapy, while a patient with levamisole-induced disease needs, above all, to stop the exposure. The condition generally improves once the offending drug is removed, and aggressive immunosuppression is only needed short-term to control the acute flare. Some patients have been treated successfully with a combination of plasmapheresis, which filters the offending antibodies from the blood, and short courses of immunosuppressive drugs.20PubMed. Plasmapheresis and steroid treatment of levamisole-induced vasculopathy and associated skin necrosis in crack/cocaine users
The takeaway for clinicians is that any patient presenting with vasculitis, purpura, or neutropenia who uses cocaine should be tested for levamisole exposure. And for patients, understanding this risk matters because the symptoms can appear confusing and frightening, and telling your doctor about cocaine use, though uncomfortable, could prevent weeks of inappropriate treatment.
The Aminorex Problem
Levamisole’s dangers do not end with the drug itself. The body metabolizes levamisole into aminorex, a compound that was once marketed as a weight-loss pill in the 1960s before it was pulled from the market because it caused fatal pulmonary hypertension. Aminorex acts like an amphetamine at the brain’s monoamine transporters, meaning it can release dopamine, serotonin, and norepinephrine.21PubMed Central. Aminorex, a metabolite of the cocaine adulterant levamisole, exerts amphetamine like actions at monoamine transporters This means that a person taking levamisole-adulterated cocaine is unknowingly exposed to an amphetamine-like substance on top of the cocaine, with added cardiovascular and pulmonary risks that neither drug alone would fully predict. The historical connection to pulmonary hypertension is particularly alarming, because that condition involves dangerous elevation of blood pressure in the lung’s arteries, and it can be irreversible.
This metabolic quirk also complicates drug testing. Standard urine screens for cocaine or amphetamines may not flag aminorex, and dedicated testing for levamisole itself requires specialized methods that are not available at most hospitals. The lag between exposure and clinical consequences, combined with the difficulty of detecting the drug, means many cases are likely going undiagnosed.
How Widespread Is the Problem
Measuring exactly how much of the cocaine supply contains levamisole is difficult because the answer varies by region and shifts over time. What is clear is that levamisole’s presence has grown substantially since it was first identified as a cocaine adulterant and that measurement in human samples has become an increasing focus for toxicology labs.22PubMed. Bioanalytical methods for quantitation of levamisole, a widespread cocaine adulterant Though it remains available for legitimate veterinary use globally, its human medical options outside the United States and illicit availability worldwide ensure that the supply chain for adulterating cocaine remains uninterrupted.3Therapeutic Drug Monitoring. Levamisole—a Toxic Adulterant in Illicit Drug Preparations: a Review
One creative approach to tracking levamisole at a population level involves monitoring wastewater. By analyzing sewage for chemical biomarkers, public health researchers can estimate how much of a given drug a community is consuming without relying on self-reports or hospital admissions. A recent study using automated real-time wastewater surveillance found that levamisole loads rose on weekends and during public events, closely tracking the pattern of cocaine’s primary metabolite, confirming that levamisole remains a persistent companion of cocaine in the drug supply.23PubMed. Intraday trends of chemical biomarkers in wastewater monitored through automated real-time surveillance That kind of data is valuable because it captures consumption patterns across an entire population, including people who never interact with the healthcare system.
Veterinary Resistance and the Ongoing Supply
Levamisole’s continued availability is partly a consequence of its importance in veterinary medicine, where it remains a widely used dewormer for livestock. But even in that role, the drug faces challenges. Parasitic worms have developed resistance to levamisole in many regions. Research on the blood-feeding stomach worm of sheep found that resistance to levamisole is an incompletely recessive trait influenced by multiple genes, meaning it builds up gradually in worm populations under selection pressure from repeated drug use.24ScienceDirect (International Journal for Parasitology). Inheritance of levamisole and benzimidazole resistance in an isolate of Haemonchus contortus As resistance spreads, farmers in some regions have moved to other dewormers, but in many parts of the world levamisole remains cheap enough and effective enough to sustain high production volumes. Those volumes, in turn, sustain the supply available to drug traffickers.
There is a grim irony in the situation. A drug that was once considered safe enough for human cancer patients, and remains safe enough for routine use in livestock, has become one of the more dangerous substances in the illicit drug supply, not because it is inherently deadly at the doses used, but because it is consumed repeatedly, without medical monitoring, by people who do not know they are taking it. The immune-related side effects that were manageable under clinical supervision, where doctors could check blood counts and stop the drug at the first sign of trouble, become catastrophic when no one is watching. The white-blood-cell crash, the skin necrosis, the brain inflammation, all these complications are in principle detectable early and often reversible if caught in time. The tragedy is that by the time most people learn they have been exposed, the damage is already severe.