Female subjects who had received naltrexone gained 40% less weight six months later and 20% less weight a year later than did those who had received a placebo. Naltrexone had no impact on weight gain in male subjects, however. The reason why it helped women, but not men, the researchers suggested, may be because "the opioid system has been shown to be involved in sweet and palatable food intake, eating hedonics, and sugar bingeing, [and] women are more likely than men to have disordered eating and binge on high-fat and sweet foods."
Naltrexone also reduces alcohol craving by blocking the mu opioid receptor. It was approved by the Food and Drug Administration more than a decade ago for treating alcohol dependence. See Psychiatric News for information on that topic. However, naltrexone seems to benefit certain individuals with alcohol dependence more than others depending on which variant of the gene that makes the mu opioid receptor they've inherited. Read more about that in Psychiatric News as well. To read about a naltrexone implant in drug addiction patients, see the American Journal of Psychiatry.