Lab tests had shown that cocaine affects animals too, as one would expect. Now the drug has been tested on wild animals
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Lab tests had shown that cocaine affects animals too, as one would expect. Now the drug has been tested on wild animals
08:38 AM • April 23 2026 IDT
Cocaine may be fun at parties but physiologically it is a stimulant that may trigger negative experiences, from pounding heart to anxiety to tremors, seizures and death. There's also an addictive facet. Now, thanks less to drug lords and more to addicts the world over using toilets, cocaine has reached the wild.
The question is what effect it has there. This was examined by Jack Brand and colleagues reporting in the Cell Press journal Current Biology on Monday, in the first experimental investigation into how cocaine pollution impacts wild baby salmon, as opposed to lab fish and their ilk.
The drug is famously a pastime strictly for the rich. Is cocaine in the water seriously a problem? Yes, in some places; and it isn't because frowning cops are throwing drug lords' stashes into the sea. It's because despite its price, cocaine use has become so prevalent that it and its derivatives have become detectable in sewage; it leaks from manufacturing facilities; and such are the vagaries of international trade, that some just gets lost.
About 292 million people are estimated to have taken illegal drugs in 2022 and of that, almost a tenth are thought to have used coke. All of them pee, and depending on the quality of their dealers and of the local waste water treatment, some of that coke and its metabolite winds up in the water.
In the lab, we already know that cocaine affects other terrestrial and marine animals. One 2021 study found that cocaine given to Perna perna mussels "triggered a complex pattern of neuroendocrine responses," and lists them at length. Separate work showed that rats given alcohol before being given cocaine were more prone to develop addiction.
We need to know what impact cocaine has on wild animals because we care, or at least we eat them, and there are already enough drugs-of-abuse in some waters for seafood to come out positive in drug tests. In 2024 the world went crazy for the "cocaine sharks" of Brazil – were they eating bales of cocaine lost at sea? We still don't know but the fact is that 13 sharpnose sharks caught by Rio de Janeiro, home to many a drug production lab, tested positive for coke.
The next year, researchers reported on the global occurrence and distribution of recreational and medical drugs in rivers, testing for example for cocaine, amphetamine, methamphetamine, the "party drug" MDMA, ketamine and opioids such as fentanyl (which has a half-life of 45 hours in rivers). The rivers of the south and north Americas are more afflicted with stimulants like cocaine while opioid levels were higher in African rivers.
But it had not been clear how pollution from the crap-tons of coke humankind is snorting or injecting or swallowing or misplacing affects creatures in the wild. The underlying assumption was that even small concentrations in the sea, river or lake may have potency because cocaine interacts with neurological mechanisms that are the same in us and other creatures, the team explains.
A key problem to checking how drugs affect animals in the wild is controlling the parameters. Concentrations of the drug, administration of it, how the animal takes it up, et cetera – those can vary enormously. Yet now a team has cracked that conundrum.
How did they control the parameters? Slow-release cocaine implants, designed from the fish's perspective to emulate cocaine in the water, were inserted into in 2-year-old smolts of wild Atlantic salmon. The juvenile smolts were then released into in Sweden's Lake Vattern. Then the team studied how they behaved compared with peers with implants, but that had not been dosed.
This large-scale field experiment was done in Sweden's Lake Vattern, which is not some piddling pond but a vast body of freshwater over 1,900 square kilometers in surface area.
Before the experiment, they tested its water for illicit drugs within a kilometer of the release site. Why yes, they did find traces cocaine and its metabolite but at low enough levels not to confound the experiment, Brand confirms. Crucially, in a parallel laboratory experiment, smolts housed in local freshwater from the environment without implants had no detectable cocaine or benzoylecgonine in their brain or muscles, suggesting the lake didn't have enough of the drug to affect its fish.
Indeed, if the lake had a lake had a cocaine problem, it would have confounded the experiment, but it didn't, he confirms.
To be clear, salmon do not naturally occupy Lake Vattern. The landlocked lake is annually seeded with baby Atlantic salmon to replace a particularly burly species of trout that went extinct in the 1920s. That is sad.
"They don't migrate to sea and back, and the lake is stocked annually with hatchery-reared juveniles to support a recreational fishery (including catch-and-release-or-keep angling). We took advantage of that existing stocking program for our release," Brand explains.
So they chose Lake Vattern because it didn't have a cocaine problem, it had fish tracking equipment in place, and salmon were being stocked there annually anyway so people wouldn't miss the trout. Also, using stocked fish gave them experimental control over the parameters: all the salmon were the same age and size.
How were the slow-release capsules implanted? "Under anaesthesia, we made a small incision in the abdomen and inserted a slow-release implant - essentially a small volume of a fatty substance with a known concentration of cocaine or benzoylecgonine dissolved in it," Brand says. "The fat-based substance releases the drug gradually over time, mimicking the chronic low-level exposure a fish would experience swimming in polluted water."
Don't try that at home with the goldfish, kids. "At the same time and through the same incision, we inserted an acoustic tag so the fish only had to be anesthetized once," Brand adds. "This allowed us to track the fish once they were in the lake. The control group received an identical surgery and an identical fatty implant, just without any drug." And the results?
You could say that fish on coke danced all night, to paraphrase what Brand and his colleagues discovered. The implants didn't cause a higher death rate; and as for behavior, smolts implanted with cocaine ranged roughly twice as far as their sober peers from the point of release into the lake.
On average the control fish reached a maximum of about 19–20 kilometers from the release site, and that didn't really change over the eight-week experiment. Fish exposed to the metabolite kept pushing farther, reaching about 32 kilometers from release in the final two weeks of the study.
That is a 60 percent increase in dispersal distance, which is not a small effect, Brand tells Haaretz by email. Those salmon were hyper.
One wonders how fish metabolize cocaine. Do they metabolize cocaine, and is it into benzoylecgonine like in us? "The conversion seems to be much less efficient in salmon than it is in humans, where benzoylecgonine usually builds up to higher levels in blood than the cocaine itself," Brand answers. "This usually results in greater levels of benzoylecgonine actually being excreted into the environment by people.
"This is partly what makes our results so interesting," he adds. "We found that this metabolite is likely posing a more substantial risk to fish in highly polluted habitats than was previously appreciated – perhaps even more so than cocaine itself."
Oy. "In humans, benzoylecgonine is generally considered largely inactive – a breakdown product on its way out of the body," he explains. But apparently in fish, separate lab work suggests it drives larger changes.
Why might fish on coke or benzoylecgonine swim so much more? Same reason we do when on coke. It's a psychomotor stimulant. In fact, the fact that fish on coke swim "frantically" (not their word) was not unexpected.
Why benzoylecgonine rather than coke drives fish to swim madly is less obvious, he adds. "Honestly, the mechanism is one of the open questions our paper raises. We can show the behavioral effect clearly, but explaining exactly why it happens at a neurochemical level will take follow-up work."
So what have we? The first study to mimic coke and metabolite concentrations that fish would experience in "nature" near relevant cities, and to check their effect on said fish. The amounts used mimic the case near cities marked for high cocaine use. The fish went psychomotorically nuts. You stand warned.
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