Effects of nalmefene on eating were investigated in two groups of ten male 
volunteers, in a double-blind placebo-controlled study. The nalmefene treated 
group ate 22% less, both in terms of absolute weight and caloric intake, of a 
standardised buffet-meal than did the placebo group. No differences in 
subjective ratings of hunger or satiety were found between the groups, 
suggesting that the reduced feeding was not a consequence of any change in 
motivation to eat. When analysed by nutrient content, nalmefene was found to 
reduce fat and protein, but not carbohydrate, intakes. Analyses of intakes of 
individual foods showed a differential effect of nalmefene on foods rated as 
highly palatable. Thus the apparent nutrient specificity of nalmefene appeared 
to be an indirect consequence of its effect on palatability. Nalmefene also 
caused slight increases in self-rated alertness, and decreases in ratings of 
tiredness and elation, although it was thought unlikely that these accounted for 
observed changes in eating behaviour. No other side-effects were detected, and 
performance on a choice reaction time task was unaffected. These results add 
weight to suggestions that endogenous opioids are involved in reward-related 
aspects of feeding associated with food palatability.