Effects of naltrexone on alcohol self-administration in heavy drinkers

The mechanisms underlying the suppressant effects of naltrexone (NTX) on ad libitum alcohol drinking in a bar/restaurant setting were investigated in heavy beer drinkers. Fifty-one male and female heavy drinkers (mean age = 2 2) received 50 mg of NTX or placebo (PBO), p.o., on two separate occasions in a randomized, double-blind crossover protocol. After 7 days of taking me dication, subjects were provided with the opportunity to consume beer ad li bitum during two, 90-min test sessions that were held 1 to 2 weeks apart. B lood samples were collected on test days to ensure medication compliance an d to measure blood levels of NTX and the active beta-naltrexol, Less beer w as consumed during NTX treatment. NTX decreased urges to consume alcohol, N TX-treated subjects also took significantly longer to finish each glass of beer and were more likely to terminate beer drinking early. Self-report sti mulation and ratings of positive mood states were lower during NTX treatmen t. Negative side effects of NTX, such as nausea and headache, were reported more frequently with NTX, Not all of the subjects decreased their beer int ake on NTX, and some subjects drank more beer. Nonresponders to NTX were no t related to blood levels of the active metabolite beta-naltrexol or to a f amily history of alcoholism. Overall, the results of this study suggest tha t NTX affects a number of the components of alcohol drinking sequence, incl uding lowering cravings, decreasing the positive reinforcing effects of alc ohol, and increasing headache and nausea, each of which may contribute to r educing alcohol intake.