Study Suggests Anti-Anxiety Medication Exposure Is Making Salmon Take Greater Risks

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Research indicates that Atlantic salmon exposed to a common anti-anxiety medication exhibit faster migration, raising concerns about ecological implications

Sara Hashemi – Daily Correspondent

April 16, 2025 1:02 p.m.

In an era where human medication use is prevalent, traces of these substances often infiltrate ecosystems, even after wastewater treatment processes. Approximately 1,000 distinct pharmaceutical compounds have been identified in waterways globally, extending even to regions like Antarctica. Recent findings reveal the potential impacts of these contaminants on wildlife behavior, notably among aquatic species.

“Pharmaceutical pollution, or chemical pollution, is an often overlooked but significant factor in global environmental change,” states Jack Brand, the principal investigator and an environmental scientist at the Swedish University of Agricultural Sciences. He emphasized to Benji Jones at Vox that such pollution poses risks that may be underestimated by the public and represents a critical challenge for aquatic ecosystems.

To investigate these concerns, Brand’s research team administered clobazam—a drug commonly used for anxiety and sleep disturbances—to juvenile Atlantic salmon in dosages reflective of those likely encountered in nature. The researchers utilized tracking technology to observe the influences of the drug on the fish’s migration route from the Dal River in Sweden to the Baltic Sea, a distance of approximately 17 miles.

Results indicated that the clobazam-treated salmon demonstrated a higher likelihood of reaching the Baltic Sea, showing an accelerated passage through significant hydropower dams that typically impede fish movements. These revelations were published in the journal Science recently.

Experts hypothesize that the altered migration patterns could stem from an heightened propensity for risk-taking in the drugged fish. “This interaction between two environmental challenges is fascinating,” comments Olivia Simmons, a salmon ecologist from the Norwegian Institute for Nature Research, while discussing the findings with Rebecca Dzombak at the New York Times. She notes that “these bolder salmon might be swimming faster due to reduced inhibitions.”

However, enhanced speed could lead to detrimental outcomes for the salmon population. “It is crucial to recognize that alterations in natural behaviors and ecology may lead to broader negative impacts on the species and other wildlife within the ecosystem,” cautions Marcus Michelangeli, a co-author and behavioral ecologist at Griffith University in Australia, in a statement.

Brand further elaborates to Jonathan Lambert at NPR that clobazam exposure may result in salmon becoming more solitary and prone to risk-taking, effectively leading them through obstacles without waiting for their companions.

In laboratory observations, the researchers noted additional solitary behaviors in clobazam-treated salmon. These fish tended to avoid forming schools, even in the presence of predators such as northern pike, which could increase their risk of predation.

“It’s akin to playing cards,” explains Giovanni Polverino, a behavioral ecologist at the University of Tuscia in Italy, who was not associated with this research, when discussing the implications of risk-taking behavior in animals. “Higher risks can lead to greater losses, including life-threatening situations for the fish.”

Despite these challenges, there is optimism regarding the future for fish populations as highlighted by Michelangeli. Advances in wastewater treatment technologies are showing promise in reducing pharmaceutical pollutants, and scientists are actively pursuing the development of medications that break down more swiftly in the environment.

“By innovating pharmaceuticals that degrade faster or lessen their environmental impact after use, we can significantly lessen the negative effects of pharmaceutical contamination in aquatic ecosystems in the future,” he emphasizes.

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