Cocaine is almost never pure by the time it reaches a user. At the street level, the average purity of cocaine in the U.S. is about 83%, meaning roughly one-fifth of what someone buys is something other than cocaine. What makes up that other portion ranges from harmless fillers like sugar to dangerous contaminants like fentanyl, and the specific mix varies by batch, region, and supplier. Understanding what’s in the supply matters because many of the most serious health consequences attributed to cocaine actually come from what it’s cut with.
Inert Fillers: Bulking Up the Product
The simplest and most common cutting agents are sugars and starches. These are cheap, white, powdery, and dissolve easily, making them nearly impossible to distinguish from cocaine by appearance alone. Lactose, mannitol, and inositol are among the most frequently used. They’re pharmacologically inactive, meaning they don’t produce any drug effects on their own. Their only purpose is to increase volume so dealers can sell less cocaine for the same price.
These fillers carry minimal health risk when snorted, though they can cause minor nasal irritation over time. They’re considered the least dangerous category of adulterant, but their presence is essentially universal. Even wholesale-level cocaine, which averages about 88% purity according to 2024 DEA data, contains some amount of non-cocaine material.
Local Anesthetics: Faking the Numbness
One of the ways people test cocaine informally is by rubbing it on their gums. If it causes numbness, they assume it’s potent. Dealers exploit this by adding local anesthetics like lidocaine, procaine, and benzocaine, all of which produce the same numbing sensation cocaine does. These agents mimic cocaine’s anesthetic effect, masking the product’s reduced purity.
What they can’t replicate is cocaine’s high. Local anesthetics interact with some of the same nerve pathways, but their effects are insufficient to produce cocaine’s stimulant or euphoric properties. The danger is that users feel the expected numbness and assume they’re getting strong cocaine, then take more to chase the high they’re not getting, increasing their exposure to whatever else is in the batch. Lidocaine in particular can affect heart rhythm at high doses, which compounds the cardiac stress cocaine already causes.
Levamisole: The Most Widespread Adulterant
Levamisole is a veterinary deworming drug, and it is by far the most pervasive active adulterant in the cocaine supply. DEA testing found it in 73% of seized cocaine specimens in 2009, and subsequent estimates put the figure above 80%. A hospital study of urine samples from cocaine users found levamisole in 78% of those that tested positive for cocaine.
Why a cattle dewormer ends up in cocaine isn’t entirely clear, but it’s likely added at the production stage in South America rather than by street-level dealers. Some researchers believe it may enhance or prolong cocaine’s effects by interacting with the brain’s reward pathways, which would make it attractive to producers looking to stretch their product without complaints from buyers.
The health consequences of levamisole are severe. It can cause a condition called agranulocytosis, where the body’s white blood cell count drops dangerously low, leaving a person unable to fight off infections. It also triggers a painful skin condition called cutaneous vasculitis, where blood vessels in the skin become inflamed, leading to dark, necrotic patches that often appear on the ears, nose, and cheeks. Hospitals in cities with high cocaine use have reported clusters of patients presenting with these symptoms, and levamisole is now a recognized cause. Because it’s added before cocaine reaches the country, there’s essentially no way for a user to avoid it without laboratory-grade testing.
Stimulants: Caffeine and Beyond
Other stimulants are sometimes added to cocaine to boost or mimic its energizing effects. Caffeine is among the most common. It increases heart rate, raises blood pressure, and produces a sense of alertness that can partially mask diluted cocaine. When combined with cocaine, caffeine compounds the cardiovascular stress. Both substances independently affect the heart’s electrical signaling, and together they increase the risk of irregular heart rhythms. In people with undiagnosed heart conditions, this combination can be especially dangerous.
Amphetamines and other synthetic stimulants occasionally appear as well, though less consistently than caffeine. These add unpredictability because their onset, duration, and intensity differ from cocaine’s short-acting profile, making it harder for a user to gauge what they’ve taken.
Phenacetin: A Hidden Kidney Threat
Phenacetin is a painkiller that was pulled from most markets decades ago because of its toxicity, but it remains a common cocaine adulterant in some regions. It’s white, powdery, and cheap, making it an easy filler. The problem is that regular exposure to phenacetin causes serious kidney damage, including scarring of the tiny blood vessels inside the kidneys. A long-term epidemiological study found that regular phenacetin users had a 16-fold increased risk of dying from kidney or urological disease compared to non-users, along with nearly triple the risk of fatal cardiovascular disease. People who use cocaine regularly may be accumulating kidney damage from phenacetin without realizing the source.
Fentanyl: The Deadliest Contaminant
The most dangerous substance found in cocaine today is fentanyl, a synthetic opioid that is active in microgram quantities. Unlike most cutting agents, fentanyl isn’t added to enhance or mimic cocaine’s effects. It likely enters the supply through cross-contamination during production or packaging, or is added deliberately by some sellers. Because fentanyl is lethal in doses as small as two milligrams, even trace amounts in a cocaine batch can cause a fatal overdose.
The numbers reflect this. In 2023, there were 29,449 cocaine-involved overdose deaths in the United States, and nearly 70% of stimulant-involved overdose deaths that year also involved illicitly manufactured fentanyl. Fentanyl has been the main driver of the rise in cocaine-related deaths since 2015. Many of these deaths occur in people who didn’t intend to take an opioid at all.
This is particularly dangerous because cocaine users typically have no opioid tolerance. A dose of fentanyl that might not kill someone who regularly uses heroin can stop breathing in someone whose body has never encountered an opioid.
How People Test for Contaminants
Fentanyl test strips are the most accessible tool for checking cocaine for fentanyl contamination. They cost a few dollars each and work by detecting fentanyl in a dissolved sample. The process is straightforward: dissolve a small amount of the drug (at least 10 mg) in about half a teaspoon of water, dip the strip for 15 seconds, then lay it flat and read the result after two to five minutes. A single pink line means fentanyl was detected. Two lines means it wasn’t.
These strips have real limitations. They can’t tell you how much fentanyl is present, only whether it’s there. They may miss some fentanyl analogs like carfentanil. And because fentanyl isn’t always evenly distributed throughout a batch, one portion might test negative while another contains a lethal dose. Still, they’re the most practical option currently available and are considered a meaningful harm reduction tool by the CDC.
For other adulterants like levamisole, lidocaine, or phenacetin, there’s no simple at-home test. Some drug-checking services use more advanced methods to identify a broader range of substances, but these aren’t widely available in most areas. Reagent testing kits sold online can confirm the presence of cocaine itself but generally can’t identify specific cutting agents.
Why Purity Varies So Much
Cocaine gets cut at multiple points along the supply chain. At the wholesale level, where large quantities change hands, average purity runs around 88%. By the time it’s broken into smaller amounts for street sale, purity drops to about 83% on average, with individual samples varying widely. Some batches test well above 90%, while others fall below 50%. Each time the product changes hands, there’s an opportunity for someone to add filler and increase their profit margin. The result is that two purchases from the same city, even the same seller, can contain very different substances and very different levels of actual cocaine.