Many pharmacies don’t provide patients with instructions on how to properly dispose of unused opioids and antibiotics, according to a new study.

Researchers surveyed California pharmacies, and found that fewer than half provided disposal instructions that met Food and Drug Administration (FDA) guidelines, Time reports.

The study found 43% of pharmacy workers knew how to deal with antibiotics, while only 23% knew what to do with opioids. Just 10% followed the FDA’s preferred recommendation to take back unused medications from customers.

“The FDA has specific instructions on how to dispose of these medications, and the American Pharmacists Association has adopted this as their standard. Yet it’s not being given to the consumer correctly the majority of the time,” lead researcher Hillary Copp said in a news release.

Unused opioids should not be left in a medicine cabinet, since they can fall into the wrong hands, the researchers noted. The FDA recommends that if a take-back option is not readily available, opioids should be flushed down a toilet, since people may otherwise find and accidentally ingest or intentionally abuse them, even when they have been mixed with an unpalatable substance and thrown into the trash.