Tramadol is a mu
opioid agonist that also inhibits the reuptake of
norepinephrine and
serotonin. Because non-medical use of prescription
opioids, including
tramadol, has increased in the U.S. over the last several years, we sought to profile its subjective, psychomotor, and physiological effects in
recreational drug users. Twenty-two subjects received placebo, 50 or 100 mg
tramadol,
morphine, or 2 mg
lorazepam in a randomized, crossover, double-blind design. The last 12 subjects in the study received 25 mg
morphine, a dose that is putatively equianalgesic to 100 mg
tramadol. In these subjects,
morphine induced
miosis and several other mu agonist subjective effects; 100 mg
tramadol increased "feel drug effect" and drug liking ratings, and decreased pupil size, but the
miotic effect was not statistically significant.
Lorazepam, but neither
tramadol nor
morphine, impaired psychomotor performance. When the placebo,
tramadol, and
lorazepam data from all 22 subjects were analyzed, 100 mg
tramadol induced
miosis, and several subjective effects were increased significantly, including ratings of drug liking and "want to take again." The present results indicating that a clinically-prescribed dose of oral
tramadol has abuse liability-related effects in
recreational drug users suggest the need for further abuse liability testing of the oral formulation in
opioid abusers.