Most wastewater facilities do not have the capability of removing pharmaceuticals during the waste treatment process, so any drugs flushed down the toilet or drain can end up back in our drinking water. Antibiotics and hormonal drugs (e.g., birth control pills) have been found in surface water throughout the United States. Their presence is blamed for sexual changes in fish and the increasing resistance of infections to antibiotic treatment. Putting medicines in the trash is no better. Animals or humans may find and ingest them. Once the drugs make it to landfills, they can wind up in our drinking water supply.
The New York State Department of Environmental Conservation has initiated a "Don't Flush" campaign to inform consumers of the danger of improper disposal. Many municipalities are offering collections - George and I went to Ithaca's today to discard my expired medicines. If you are unable to take advantage of a safe and supervised collection, put your unwanted medicine in a closed container with an undesirable substance like cat litter or coffee grounds and tape it securely.