Cocaine can be laced with dozens of different substances, ranging from harmless fillers like sugar to potentially lethal contaminants like fentanyl. The Drug Enforcement Administration estimates that over 25% of cocaine submissions in 2024 also contained fentanyl or fentanyl-related compounds, making contamination one of the most serious risks associated with cocaine use today.
Inert Fillers Used to Add Bulk
The simplest and most common form of adulteration involves substances added purely to increase weight and volume. Sugars and starches are cheap, easy to purchase, and blend seamlessly into white powder. These fillers are pharmacologically inactive, meaning they don’t produce any drug-like effects on their own. Beyond minor nasal irritation, they carry relatively little additional health risk compared to the cocaine itself. Other common bulking agents include creatine and paracetamol (the active ingredient in Tylenol).
Local Anesthetics That Mimic Cocaine
One of cocaine’s well-known properties is that it numbs tissue on contact. Many people test their purchase by rubbing a small amount on their gums, checking for that telltale numbing sensation. Dealers exploit this by adding other numbing agents like lidocaine, benzocaine, procaine, and tetracaine. These substances block nerve signals in the same way cocaine does, so the “tongue test” can’t distinguish between pure cocaine and a heavily cut product. A sample that feels potent based on numbness alone may actually contain far less cocaine than expected.
While these numbing agents work on nerve endings similarly to cocaine, they don’t produce the same stimulant high. Their potency at the brain’s reward pathways is far too low to replicate cocaine’s euphoric effects. They exist in the supply chain purely to deceive buyers into thinking they’re getting a stronger product.
Levamisole: The Most Widespread Adulterant
Levamisole is a veterinary deworming medication found in roughly 80% of cocaine seized in the United States, according to DEA estimates. Its prevalence is striking. Unlike inert fillers, levamisole carries serious health consequences.
The most dangerous effect is agranulocytosis, a severe drop in white blood cells that cripples the immune system. People with this condition become vulnerable to infections their body would normally fight off easily. Levamisole has also been linked to a painful skin condition called cutaneous vasculopathy, where blood vessels near the skin become inflamed and damaged, sometimes leading to tissue death. The Substance Abuse and Mental Health Services Administration issued a public alert about levamisole contamination as far back as 2009, and it remains pervasive in the supply.
Research suggests levamisole may actually enhance cocaine’s effects in the body, which could explain why it became so dominant as an adulterant. It’s not just filler. It appears to synergize with cocaine’s action on the brain, giving dealers an economic incentive to use it over cheaper, inactive alternatives.
Fentanyl and Other Opioids
Fentanyl contamination in cocaine is the most acutely dangerous trend in the current drug supply. A community-based drug checking study found fentanyl in nearly 15% of powder cocaine samples, with significant geographic variation. The same study found heroin in about 7% of powder cocaine samples. Crack cocaine appeared less likely to contain fentanyl, with none detected in the samples tested.
The combination is particularly hazardous because cocaine and opioids stress the body in opposite, compounding ways. Cocaine drives up heart rate, blood pressure, and the heart’s demand for oxygen. Fentanyl simultaneously suppresses breathing, reducing the oxygen supply available. This mismatch puts enormous strain on the heart and brain. One study found that cocaine significantly decreased overall blood flow to the brain, a problem made far worse when breathing is already depressed by an opioid. For someone who uses cocaine but has no opioid tolerance, even a small amount of fentanyl can cause fatal respiratory failure.
Xylazine: A Growing Concern
Xylazine is a veterinary sedative that has increasingly appeared in the illegal drug supply, including cocaine. The CDC reports that it can be mixed into cocaine, heroin, or fentanyl either to enhance sedative effects or simply to increase the weight of a product for sale. It is not approved for use in humans.
In people, xylazine slows breathing, drops blood pressure, and reduces heart rate. It has also been associated with severe skin wounds that are prone to infection and slow to heal. Critically, xylazine is not an opioid, so naloxone (Narcan) does not reverse its effects. In the drug checking study mentioned above, the presence of xylazine dramatically reduced people’s ability to correctly identify whether fentanyl was also in their sample. Correct identification dropped from 92% to just 42% when xylazine was present, suggesting it masks or confuses the effects of other contaminants.
Other Active Adulterants
Several other pharmacologically active substances appear regularly in cocaine. Phenacetin, a painkiller pulled from many markets due to kidney damage risks, is one of the more frequently identified cutting agents in European and North American samples. Caffeine adds a mild stimulant boost that can make diluted cocaine feel slightly more potent. Diltiazem, a blood pressure medication, and hydroxyzine, an antihistamine with sedative properties, have also been found. Each of these carries its own set of side effects that users are unlikely to anticipate or recognize.
How Testing Works and Where It Falls Short
Fentanyl test strips are the most widely available harm reduction tool for checking cocaine. Originally designed for urine drug testing, these inexpensive strips can detect low levels of fentanyl in a dissolved drug sample. They work as competitive immunoassays: the absence of a visible test line means the substance tested positive for fentanyl.
However, test strips have real limitations. They are designed to detect fentanyl specifically, and while they catch many fentanyl-related compounds, they won’t reliably flag every synthetic opioid analogue. They also cannot detect xylazine, levamisole, local anesthetics, or most other adulterants. For broader screening, community-based drug checking services that use laboratory analysis provide more comprehensive results, though access varies widely by region.
Cocaine-specific test strips (used to confirm cocaine is present) were found to be roughly ten times less sensitive than their listed specifications, detecting cocaine only at concentrations about 2.5 micrograms per milliliter rather than the advertised 0.2. This matters less for fentanyl detection but highlights that test strip performance doesn’t always match the label.
Why Purity Levels Don’t Tell the Whole Story
DEA analysis shows that wholesale cocaine purity in the U.S. rose to 88% in 2024, up from 86% the year before. Higher purity at the wholesale level might seem like it would reduce adulterant exposure, but the contamination that matters most often happens further down the supply chain, closer to the point of sale. A product that starts at 88% purity at the kilo level can look very different by the time it reaches an individual buyer. Each transaction along the way creates an opportunity for someone to add fillers, numbing agents, or other substances to stretch profits. The fentanyl contamination data, showing it in over a quarter of cocaine submissions to labs in 2024, makes clear that high wholesale purity hasn’t solved the adulteration problem at street level.