An opioid antagonist, naltrexone, reduces preference for sucrose in humans

Eight healthy nonobese volunteers were asked to rate, on a pleasure-displeasure scale, sucrose and salty solutions as well as alimentary and nonalimentary odors. Effects of intragastric glucose load (vs. water load) and naltrexone (vs. placebo) were tested. Naltrexone produces a significant decrease for sweetened solution on the pleasure scale, a shift even stronger than that of the glucose load itself. Such a decrease is also observed for alimentary odors but not for responses to nonalimentary stimuli. Thus the opioid system is involved in ingestive behavior in humans, and this action is perhaps specific.