The risks of drug addiction must be more carefully balanced with the need to provide pain relief for patients recovering from urological procedures, a study published in the Journal of Urology said.

The researchers, led by Dr. Cory Bates of the University of Utah Health Sciences Center, said they noticed most patients did not take the entire supply of prescribed painkilling medication after their urological procedure, according to Reuters, meaning that the excess pills could be used recreationally.

Almost 90 percent of patients who found themselves with extra narcotics simply kept the medicine at home, which poses a risk of abuse, given that leftover pills are one of the major sources of illicit narcotics in the U.S., the study said. Forty percent of the legally prescribed painkillers in the U.S. every year go unused by the person they were prescribed for, the researchers added.

Reuters reported that excess pills should be mixed in with an unappetizing substance like coffee grounds or cat litter and thrown away, though the government's office of National Drug Control Policy should be consulted for specific disposal instructions.