Drug dealers lace their products for one overriding reason: profit. By stretching a supply with cheaper substances, a dealer can sell more product from the same starting batch. But profit maximization is only part of the story. Lacing also happens because of supply chain economics, the rise of cheap synthetics, and sometimes to alter how a drug feels to the user.
Stretching the Supply With Fillers
The most straightforward reason for lacing is bulking. Because illicit drugs are completely unregulated, they get diluted at every step of the supply chain with materials that look and feel like the original product. Common fillers include sugars, starches, and local anesthetics like lidocaine. These are cheap, easy to buy, and physically resemble white powder drugs such as cocaine or heroin. A dealer who cuts a kilogram of cocaine with an equal weight of filler has doubled their sellable product without doubling their cost.
Some cutting agents go beyond simple filler. An animal deworming compound called levamisole became one of the most common cocaine adulterants because it checks every box a dealer could want: it’s inexpensive, looks identical to cocaine, and actually prolongs and intensifies cocaine’s effects. That last property matters because it makes the cut product feel closer to the real thing, keeping buyers from noticing the dilution. From the dealer’s perspective, it’s the ideal cheat.
Cheap Synthetics Replacing Plant-Based Drugs
The arrival of illegally manufactured fentanyl reshaped the entire drug market. Fentanyl is roughly 70 times more potent than heroin at suppressing breathing, meaning a tiny amount produces a powerful effect. It’s also synthetic, so it doesn’t require poppy fields, growing seasons, or the complex logistics of smuggling a plant-based product. Manufacturing costs dropped dramatically compared to heroin, which in North America is more expensive, less potent, and harder to produce.
This cost difference created a strong incentive to replace heroin with fentanyl or to lace heroin with it. A supplier can buy a small quantity of fentanyl, mix it into a much larger batch, and sell the result as heroin or as pressed counterfeit pills designed to look like prescription medications. The DEA’s most recent lab testing found that 5 out of 10 counterfeit pills seized contained a potentially lethal dose of fentanyl. That figure has actually decreased from 7 out of 10 in 2023, but it still means half of all tested fakes could kill someone.
The economics are simple. A few grams of fentanyl can do the work of kilograms of heroin. The profit margin on that conversion is enormous, which is why fentanyl has spread so aggressively through the supply chain.
Altering How the Drug Feels
Not all lacing is about stretching product. Some additives are chosen specifically to change the user’s experience. Xylazine, an animal sedative that has spread rapidly through the fentanyl supply, is one example. Research from the National Institute on Drug Abuse suggests some people seek it out intentionally because it extends fentanyl’s short-lived euphoria. Fentanyl’s high fades quickly, which means users need to re-dose frequently. Adding a sedative that lingers in the body makes each dose last longer, which some buyers perceive as better value.
But many users report encountering xylazine without wanting it. For them, it’s simply an unwanted additive they couldn’t avoid because they had no way to know it was in their supply. This highlights a core problem with lacing: the end user rarely has any idea what’s actually in the product they’re buying.
Creating Repeat Customers
There’s a widely discussed theory that dealers lace drugs to create dependency and guarantee repeat business. The reality is more complicated than a deliberate scheme, but the underlying biology is real. All addictive substances work by flooding the brain’s reward system with dopamine, the chemical that signals pleasure and reinforces behavior. Opioids like fentanyl activate this system through a separate pathway as well, binding to the brain’s own opioid receptors. When someone unknowingly takes a stimulant laced with fentanyl, both their dopamine and opioid systems get activated simultaneously, producing a more intense reward signal than the stimulant alone would create.
Over time, repeated activation of these reward pathways causes lasting changes. The brain’s dopamine system becomes less responsive, meaning a person needs more of the substance just to feel normal. If fentanyl has been in their supply without their knowledge, they may develop physical opioid dependence and experience withdrawal symptoms they can’t explain, driving them back to the same product. Whether dealers think through this chain of events consciously or simply notice that certain batches bring customers back faster, the result is the same.
Why Lacing Is So Dangerous
The core danger of lacing is dosing unpredictability. When fentanyl is mixed into a batch of powder or pressed into pills, the distribution is rarely uniform. One pill from a batch might contain almost no fentanyl, while the next contains several times a lethal dose. Because fentanyl is active in microgram quantities (millionths of a gram), even tiny inconsistencies in mixing can be fatal. A researcher comparing the two drugs found that fentanyl is approximately 70 times more potent than heroin at suppressing breathing, which means the margin between a dose that gets someone high and a dose that stops their lungs is razor thin.
Inert fillers carry their own risks, especially for people who inject. When substances like talcum powder or cornstarch enter the bloodstream, they don’t dissolve. Instead, they travel as tiny particles that lodge in small blood vessels. Research published in JAMA documented talc and cornstarch particles embedded in the retinas, lungs, and brains of people who injected cut drugs. Finding these particles in the eyes was considered a marker that significant damage had already occurred in the lungs, where the particles accumulate first.
Testing Before Use
Fentanyl test strips offer one practical way to check a drug supply before use. Studies have found commercially available strips to be highly sensitive (96 to 100%) and highly specific (90 to 98%) when compared against gold-standard laboratory methods. They can also detect common fentanyl relatives like acetylfentanyl and furanylfentanyl. To use them, you dissolve a small amount of the substance in water and dip the strip.
The limitation is that test strips only tell you whether fentanyl is present or absent. They can’t tell you how much is in the sample, which matters because the amount varies wildly even within a single batch. A negative result also doesn’t rule out other dangerous adulterants like xylazine, levamisole, or novel synthetics that the strips aren’t designed to detect. Testing reduces risk but doesn’t eliminate it, because the fundamental problem with laced drugs is that no one in the supply chain is controlling quality or consistency.