Naltrexone is an opioid antagonist, meaning that it blocks your opioid receptors and basically prevents opioids from having an effect. Naltrexone and naloxone (another opioid antagonist) are used in treating opiate addictions.

Not an expert, but my understanding is that these receptors (and naturally occurring opioids) play a role in the reward pathways in the brain, so it's possible that naltrexone and other opioid antagonists could be effective for other types of addiction or compulsive behaviors.

Apprently its an opioid receptor antagonist and its mechanism of action for treating alcoholism isn't well understood. Since it modulates the reward system of the brain it could potentially be useful for any addictive behavior, however there's probably a reason it doesn't seem to be prescribed outside of alcoholism or opioid addiction.

I believe I read that Dr. Sinclair was thinking Naltrexone could also be used to help with any sort of addiction such as smoking or overeating. I don't think there is any clinical research to support this though in the same way there is research supporting its effectiveness with alcoholism.

Commonly used to treat opiate dependence, often a combo of buprenorphine + naltrexone