You shouldn’t flush unwanted medicines down the drain or toilet because of the environmental impact, but there are exceptions.
Use local drug-disposal programs, if possible (check with your city, county or pharmacist). If there is no disposal program, you should throw away unwanted drugs in the household trash after mixing them with some unpalatable substance (such as used coffee grounds) in a disposable container or sealable bag.
However, the Food and Drug Administration (FDA) recommends that powerful painkillers, controlled substances and a few other drugs be flushed because they can be especially harmful to children, pets and anyone they are not intended for. These drugs usually come with disposal directions.