The study, published on Monday, also showed that recent data from the United States has indicated similar patterns, including evidence that the rate of prescription opioid abuse has exceeded the rate of heroin use in American household survey populations in recent years.

    "Our study suggests that heroin use has become an increasingly marginal form of drug use among illicit opioid users in Canada, especially outside Vancouver and Montreal," said Dr. Benedikt Fischer, a researcher funded by the Canadian Institutes of Health Research (CIHR) who led the study team.

    Prescription opioids that are commonly prescribed in Canada include OxyContin, morphine, Demerol, Percodan and Tylenol 3 or 4.

    Heroin was the most commonly used opioid in only two of the seven study sites -- Vancouver and Montreal -- reported by about half of the local participants. For the majority of the participants in the other cities, prescription painkillers such ashydromorphone, morphine and oxycodone were the predominant opioidsused.

    The CIHR report suggested that the revelation has implications for drug control policy and treatment programs, which primarily focus on heroin abuse and dependence, according to Fischer.

    "Our drug control policies ought to be targeting prescription opioid abuse more effectively. But we also need to ensure we do not compromise legitimate access to and uses of prescription opioids," he said.

    As the first systematic look at illicit drug usage among street drug users, Fischer's study provided policy makers with the scientific evidence needed to improve public policy and treatment programs and is key to ultimately improving the health of Canadians, experts said.

    The results reported in this study are based mainly on a follow-up sample of 585 participants from Vancouver, Edmonton, Toronto, Montreal, Quebec City, Fredericton and St. John, who were assessed most recently in 2005.