Ever been prescribed an opioid painkiller by your doctor and kept the leftovers in your medicine cabinet when you stopped needing them? Six out of 10 Americans who’ve taken those drugs say they have done just that—suggesting that doctors often prescribe more of the pills than necessary, and that patients don’t know how to properly use, store, and dispose of the drugs.

That’s the conclusion of researchers at Johns Hopkins Bloomberg School of Public Health, after surveying 1,032 adults across the U.S. who had been prescribed opioids. Results were published in JAMA Internal Medicine.

“Keeping leftover opioids for future use is a bad idea,” says Marvin M. Lipman, M.D., Consumer Reports chief medical adviser. “It encourages inappropriate use later on, and makes it possible for other people, including children, to get their hands on these potentially dangerous and addictive drugs.”

The survey also suggests that many people keep the drugs around longer than they should in part because their doctors never cautioned them against it. Less than half of respondents said that they recalled receiving information on safe storage (49 percent) or proper disposal (45 percent) from their doctors.

The findings confirm the results of Consumer Reports’ own survey of more than 2,000 adults published last December. It found that more than 80 percent of people didn’t lock up their narcotic painkillers, including the opioids Oxycontin, Percocet, and Vicodin—even though nearly three-quarters said they had children living at home. That comes to more than 16 million households across the U.S. where powerful opioid painkillers sit unsecured in medicine cabinets, closets, and kitchen drawers.

Opioids continue to be among the most commonly prescribed medications in the U.S. and were responsible for the deaths of more than 28,000 people in 2014, more than any other year on record according to the Centers for Disease Control and Prevention.