PAUL R. STERRY/Nature Photographers Ltd/Alamy Illicit drug use is a growing global health concern that causes a financial burden of hundreds of billions of dollars in the US alone. But hidden beneath the societal costs of this human epidemic is a potential ecological crisis. As methamphetamine levels rise in freshwater streams, fish are increasingly becoming addicted. “Where methamphetamine users are, there is also methamphetamine pollution,” says Pavel Horký at the Czech University of Life Sciences. Humans excrete methamphetamines into wastewater, but treatment plants aren’t designed to deal with such substances. Because of this, as treated wastewater flows into streams, so do methamphetamines and other drugs.