"We are seeing an increase in the number of patients addicted to prescription drugs, so we wanted to better understand how they first got hooked," said Professor Richard Blondell of the University of Buffalo and senior author on the study.

"This information suggests that there is a progressive nature to opioid use, and that prescription opioids can be the gateway to illicit drug addiction."

"It also tells us that people who use prescriptions illegally may be at greater risk for subsequent heroin use than those who use prescriptions legally."

Slightly more than half of the study group -- 51 per cent -- said they first used the drugs for post-surgical pain, back pain or after an injury.

49 percent said that they were curious and/or someone they were with had the drugs.

Those who became addicted from using drugs legally prescribed for pain were more likely to be older, female, have a university degree, and more likely to take their drugs orally, rather than nasally or via injection.

Users' comments on how they got started using drugs other than for pain, and why they continued, were revealing.

'Pill parties' were a common starting point.

One person said the drug 'was handed to me by my friend, this guy I know, someone who was at the party.'

Another patient said young people are using it "like Viagra.'

When asked if any doctor had ever asked about a substance use problem before writing a prescription, of the 53 participants who answered the question, 74 per cent said no.

Professor Blondell emphasised that the prescribing physician is in the best position to prevent or address addiction in their patients.

"I tell patients that addiction can be an unintended side-effect that occurs occasionally with the use of these medications," he said.

"Doctors need to be able to help them if this occurs, so doctors will need to monitor the use of these medications closely."

"I also tell patients to discard unused medication ASAP to prevent addiction in themselves and those, such as teenage family members, who might get their hands on these leftover pills."

Image credit: Bill Barber / CC BY-NC 2.0