Abuse of prescription opioid medications has increased dramatically in the United States during the past decade, as indicated by a variety of epidemiological sources. However, few studies have systematically examined the relative reinforcing effects of commonly abusedopioid medications. The current double-blind, placebo-controlled in-patient study was designed to compare the effects of intravenously delivered fentanyl (0, 0.0625, 0.125, 0.187, and 0.250mg/70kg), oxycodone (0, 6.25, 12.5, 25, and 50mg/70kg), morphine (0, 6.25, 12.5,25, and 50mg/70kg), buprenorphine (0, 0.125, 0.5, 2, and 8mg/70kg), and heroin (0, 3.125, 6.25, 12.5, and 25mg/70kg) in morphine-maintained heroin abusers (N = 8 completers maintained on 120mg per day oral morphine in divided doses (30mg q.i.d.)). All of theparticipants received all of the drugs tested; drugs and doses were administered in non-systematic order. All of the drugs producedstatistically significant, dose-related increases in positive subjective ratings, such as ‘I feel a good drug effect’ and ‘I like the drug.’ In general, the order of potency in producing these effects, from most to least potent, was fentanyl>buprenorphine>heroin>morphine>oxycodone. In contrast, buprenorphine was the only drug that produced statistically significant increases in ratings of ‘I feel a bad drug effect’ and it was the only drug that was not self-administered above placebo levels at any dose tested. These data suggest that the abuseliability of buprenorphine in heroin-dependent individuals may be low, despite the fact that it produces increases in positive subjective ratings. The abuse liabilities of fentanyl, morphine, oxycodone, and heroin, however, appear to be similar under these experimental conditions.
