Scientists have detected low levels of a range of prescription drugs in the water supplies of 24 major metropolitan areas in the US. The drugs include antibiotics, anticonvulsants(抗痙薬), mood stabilizers, and sex hormones. When people take medications, their bodies do not absorb them entirely, and some of the drugs are passed into the sewage system; some drugs are resistant to current wastewater treatment processes, and when the treated water is released back into the environment, it often ends up as part of the drinking water supply. Such contamination is not confined to the US; studies have detected pharmaceuticals in waters throughout Asia, Australia, Canada, and Europe.