PT  - JOURNAL ARTICLE
AU  - Angela N Duke
AU  - George E Bigelow
AU  - Ryan K Lanier
AU  - Eric C Strain
TI  - Discriminative Stimulus Effects of Tramadol in Humans
AID  - 10.1124/jpet.111.181131
DP  - 2011 Jan 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - jpet.111.181131
4099  - http://jpet.aspetjournals.org/content/early/2011/04/05/jpet.111.181131.short
4100  - http://jpet.aspetjournals.org/content/early/2011/04/05/jpet.111.181131.full
AB  - Tramadol is an unscheduled atypical analgesic that acts as an agonist at mu opioid receptors and inhibits monoamine reuptake. Tramadol can suppress opioid withdrawal and chronic administration can produce opioid physical dependence; however, diversion and abuse of tramadol is low. The present study further characterized tramadol in a three-choice discrimination procedure. Non-dependent volunteers with active stimulant and opioid use (N=8) participated in this residential laboratory study. Subjects were trained to discriminate between placebo, hydromorphone (8 mg), and methylphenidate (60 mg) and tests of acquisition confirmed that all volunteers could discriminate between the training drugs. The following drug conditions were then tested during discrimination test sessions: placebo, hydromorphone (4, 8 mg), methylphenidate (30, 60 mg), and tramadol (50, 100, 200, 400 mg). In addition to discrimination measures, which included discrete choice, point distribution, and operant responding, subjective and physiological effects were measured for each test condition. Both doses of hydromorphone and methylphenidate were identified as hydromorphone- and methylphenidate-like, respectively. Lower doses of tramadol were generally identified as placebo, with higher doses (200, 400 mg) identified as hydromorphone, or opioid-like. The highest dose of tramadol increased ratings on the stimulant scale, but was not significantly identified as methylphenidate-like. Tramadol did not significantly increase subjective ratings associated with reinforcement. Taken together, these results extend previous work with tramadol as a potential medication for the treatment of opioid dependence and withdrawal, showing acute doses of tramadol exibit a profile of effects similar to opioid agonists, and may have abuse liability in certain populations.