Profiling the subjective, psychomotor, and physiological effects of tramadol in recreational drug users

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.