Colleen L. Barry, a professor of health policy and management at the Johns Hopkins Bloomberg School of Public Health and one of the researchers who conducted the survey, said the findings illustrate how few Americans recognize that such well-meaning gestures can have consequences for people susceptible to addiction.
The response is "a very sympathetic reason for very sub-optimal and problematic behavior," Barry said. Health officials need to send "a clear-cut public health message that these medications should never be shared in any circumstance."
A separate study in the same journal, also released Monday, shows that about 15 percent of people who were hospitalized for short periods submitted claims for a new opioid prescription within seven days of discharge. Of those, 42 percent also put in a claim after 90 days, indicating continued use of a painkiller.
That study, which looked at nearly 624,000 Medicare recipients who were not using opioids in the 60 days before being hospitalized, also determined that results varied widely among facilities. Patients who were more satisfied with their pain control while in the hospital "had modestly higher rates" of opioid use after being released. But the researchers, led by Anupam B. Jena at Harvard Medical School's Department of Health Care Policy, did not determine whether that was because of appropriate or inappropriate prescribing.
Many authorities believe that over-prescribing of painkillers by physicians, coupled with illegal diversion and sharing of narcotics, have helped fuel the nation's prescription-drug epidemic. Nearly 165,000 people have died of overdoses from prescription-opioid medications such as oxycodone, hydrocodone and morphine since 2000.
According to a survey conducted by the federal Substance Abuse and Mental Health Services Agency, half of people who misused prescription painkillers got them from a friend or relative, while 22 percent got them from a doctor. The survey, conducted in 2013 and 2014, also showed that 4.3 million Americans had engaged in "non-medical use" of prescription painkillers in the previous month.
In March, the Centers for Disease Control and Prevention issued guidelines that urge doctors to use more caution in prescribing narcotic painkillers. That includes using non-narcotic alternatives, prescribing the lowest effective dose of a drug and limiting the number of doses to the smallest possible.
In the Hopkins survey, 57 percent of respondents said they have or expect to have leftover medication. That included more than 60 percent of people who no longer were using the painkillers and 53 percent of those who were still taking them. Almost half said they would hold on to the drugs for future use.
Some were expecting to get rid of their leftover pills, either by flushing them down the toilet (14 percent), putting them in the trash (7 percent), throwing them out after mixing them with something to prevent further use (6 percent) or turning them into a drug store or returning them to a "take-back" program (12 percent).
Barry said authorized take-back programs, such as those run by the federal Drug Enforcement Administration, are very difficult for most people to find. Drug stores generally will not accept medication containers that have been opened, she said.
More troubling, she noted, is that just 21 percent of the people surveyed said they kept their painkillers in a place that locks or latches -- with less than 9 percent saying their medication was in a location that could be locked.
"The overwhelming majority with these prescriptions in their homes are keeping them in locations that are very accessible" to young children who might find them accidentally and young adults who might experiment with them, Barry said. That includes nightstands, counter-tops and briefcases.
Nearly half of the survey's respondents said they had received no information on safe storage or proper disposal of painkillers.