We conducted a study in which the rewarding effects of propofol were assessed in humans, using a discrete-trials choice procedure. Normal healthy volunteers (n = 12) were exposed in a blind fashion to acute bolus injections of 0.6 mg/kg of propofol twice and to a similar volume of Intralipid twice. Then, for the next three sessions, subjects chose which drug (identified by a color code) they wished to receive. We defined propofol choosers if individuals chose propofol two or three times, and nonchoosers if they chose propofol once or not at all. By using a chi 2 goodness-of-fit test of a random choice model, the choice distribution differed significantly from a random choice distribution (P < 0.005). Six subjects were choosers: four subjects chose propofol on all three choice occasions and two subjects chose the drug on 2/3 occasions (referred to hereafter as propofol choosers). Six subjects were nonchoosers: five subjects chose Intralipid on all three choice occasions, and one subject chose Intralipid twice (referred to hereafter as propofol nonchoosers). During sampling sessions, propofol choosers reported pleasant acute effects and no unpleasant residual effects, whereas propofol nonchoosers reported either unpleasant acute subjective effects and/or residual effects from propofol. We conclude that 1) propofol may be rewarding (reinforcing) in some individuals without a history of drug abuse, and 2) further abuse liability testing is needed with this drug.

This study provides evidence that degree of impairment caused by sedative and analgesic drugs used in ambulatory surgery is similar to that obtained with a dose of alcohol that produces a blood alcohol concentration of 0.11%. We suggest that anesthesiologists can use alcohol as a standard by which to assess degree of impairment produced by drugs used for sedation/analgesia.

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