Flushing Your Anti-Anxiety Pills Down the Toilet Could Affect the Behavior of Wild Fish

A study shows that wild perch are less fearful, eat faster and are more anti-social when exposed to a common pharmaceutical pollutant

wild perch
A study shows that wild perch are less fearful, eat faster and are more anti-social when exposed to a common pharmaceutical pollutant. Image via Bent Christensen

It’s obvious that anti-anxiety medicines and other types of mood-modifying drugs alter the behavior of humans—it’s what they’re designed to do. But their effects, it turns out, aren’t limited to our species.

Over the past decade, researchers have repeatedly discovered high levels of many drug molecules in lakes and streams near wastewater treatment plants, and found evidence that rainbow trout and other fish subjected to these levels could absorb dangerous amounts of the medications over time. Now, a study published today in Science finds a link between behavior-modifying drugs and the actual behavior of fish for the first time. A group of researchers from Umeå University in Sweden found that levels of the anti-anxiety drug oxazepam commonly found in Swedish streams cause wild perch to act differently, becoming more anti-social, eating faster and showing less fear of unknown parts of their environment.

The research group, led by ecologist Tomas Brodin, put wild perch in water with 1.8 micrograms of oxazepam diluted per liter—a level consistent with samples taken from surface waters near human development around Sweden. After 7 days swimming in the contaminated water, the perch had levels of the drug in their tissues that were similar to those of wild perch samples, indicating that the pharmaceutical was being absorbed into their bodies at rates similar to what’s happening in rivers and streams.

When they closely observed the behavior of these contaminated fish, the results were unmistakable. Those dosed with the anti-anxiety drug were more active, more willing to explore novel parts of their environment and more likely to swim away from the rest of their group as compared to fish that were kept in pristine waters. They also ate faster, finishing a set amount of plankton in a shorter time.

The researchers also included a third group of fish, exposed to levels of the drug way higher than those present in the environment. All of the changes shown in the fish exposed to the mild level of the drug were greatly exaggerated in this group, indicating that the drug was indeed responsible for the behavioral changes observed.

The idea of drug-addled fish might be funny, but the researchers say it could be a troubling sign of the way mounting levels of water-borne pharmaceuticals are affecting natural ecosystems. Because perch and other predator fish play a key role in food webs, altered foraging behavior—say, eating more prey—could lead to proliferation of the algae that their prey typically eat, upsetting an ecosystem’s balance as a whole. Or, if wild perch are engaging in more risky behavior (exploring parts of their environment they usually shy away from) it could lower the species’ survival rate.

Additionally, the research group worries that the drug could affect a broad spectrum of wildlife, because the particular receptor it binds to in the brain is widely distributed among aquatic species. And Oxazepam is far from the only drug that’s been found to pollute aquatic ecosystems—in the U.S., traces of over-the-counter painkillers, birth control hormones and illegal drugs have all been detected. “That environmentally relevant concentrations of a single benzodiazepine affect fish behavior and feeding rate is alarming, considering the cocktail of different pharmaceutical products that are found in waters worldwide,” the researchers note in the paper.

These drug molecules can enter the environment in a few different ways. The practice of flushing old pills down the toilet is the first that probably comes to mind—and the easiest to prevent—but many pharmaceutical pollutants result from drug molecules that are ingested properly, go through the human body, pass out in urine and make it through wastewater treatment plants and into the environment. ”The solution to this problem isn’t to stop medicating people who are ill but to try to develop sewage treatment plants that can capture environmentally hazardous drugs,” Jerker Fick, one of the paper’s co-authors, said in a statement.

Get the latest Science stories in your inbox.