New York, Aug 18 (IANS): The use of heroin is not only increasing, but it is now being coupled with the abuse of prescription painkillers, says a new study.

The heroin-prescription drug combination is also hitting groups that were not traditionally viewed as widespread opiate users, said Shannon Monnat, assistant professor of rural sociology, demography, and sociology at Pennsylvania State University in the US.

The recent trend is a domino effect of addiction that began in the 1980s and 1990s when the over-prescription of painkillers led to an increase in addiction to those drugs, she explained.

"Over the last several years there have been more restrictions put in place, including prescription-drug monitoring programs and the introduction of a tamper-proof opioid, making it difficult to crush, liquefy and inject the substance," Monnat said.

"What this has done is restrict access to prescription painkillers for people who previously became addicted to them. These people sometimes transition into heroin, which has become incredibly cheap and easily accessible," she pointed out.

The researchers used data from the 2010-2013 National Survey on Drug Use and Health.

Some addicts who were introduced to heroin also turn to abusing both painkillers and heroin at the same time.

While most opiate addicts are still addicted to only painkillers, the number of addicts using heroin and the number of users who are addicted to both painkillers and heroin are increasing faster than painkiller-only abusers.

"You do not eliminate the addiction simply by eliminating access to the drug," Monnat said.

"People who are addicted to the morphine substance will find a substitute," she noted.

The findings appeared online in the journal Addictive Behaviours.