Atlantic salmon migrate every year from the Swedish River Dal to the sea, and pharmaceutical waste in the water may be affecting this behavior.

A research team from the Swedish University of Agricultural Sciences and Griffith University’s Australian Rivers Institute found that juvenile salmon exposed to the anti-anxiety drug clobazam were more likely to complete the migration and quicker than unexposed fish. The painkiller tramadol had similar effects, suggesting the drugs disrupt social dynamics and influence risk-taking behaviors.

While this may seem like a positive outcome, the researchers warn that any drug-induced change to natural behavior could have unpredictable and potentially harmful consequences for individual species and wider ecosystems. Published in Science, the findings highlight the growing concern around pharmaceutical pollution, especially psychoactive substances, and underscore the need for improved wastewater treatment.

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