A growing number of people switch back and forth between prescription painkillers and heroin, experts tell The New York Times. They call prescription opiates “heroin lite.”

“The old-school user, pre-1990s, mostly used just heroin, and if there was none around, went through withdrawal,” said Stephen E. Lankenau, a sociologist at Drexel University. Today, he said, “users switch back and forth, to pills then back to heroin when it’s available, and back again. The two have become integrated.”

Some young people are introduced to opiates through prescription painkillers. For people in recovery, painkillers can set off heroin craving. “You can get the pills from so many sources,” said Traci Rieckmann, an addiction researcher at Oregon Health & Science University (OHSU). “There’s no paraphernalia, no smell. It’s the perfect drug, for many people.”

About half of the 200 people being treated for heroin addiction at the Cleveland Clinic’s Alcohol and Drug Recovery Center every month started on prescription opiates, according to addiction specialist Dr. Jason Jerry. “Often it’s a legitimate prescription, but next thing they know, they’re obtaining the pills illicitly,” he said. They realize heroin is much less expensive than pills, so they switch.

People who have gone through rehab may be vulnerable to an overdose because they don’t realize their tolerance level has dropped, according to Dr. Nicholas L. Gideonse, the medical director of OHSU Richmond Community Health Center in Portland.