I stumbled upon this and thought it was interesting. This is from the archives of drug abuse.gov and it has all of the studies for naltrexone and how the funding got started (very interesting). It may be a tad lengthy, but I found it very informative. https://archives.drugabuse.gov/pdf/monographs/09.pdf

"Naltrexone was approved by the FDA in 1984 on the basis of its pharmacological efficacy as a narcotic antagonist and its safety profile. Although clinical efficacy data in the multi-site placebo controlled clinical trial were inconclusive, naltrexone was superior to placebo in producing less heroin use and more abstinence in those who tested the naltrexone blockade by using heroin at least once. In 1995, Naltrexone was approved by the FDA for the new indication of preventing relapse to alcohol use in formerly dependent alcoholic patients (Vocci)." http://archives.drugabuse.gov/meetings/Naltrexone.html

It's been around for such a long time and yet it's still such a secret.

I think a good part of that is due to the abstinence headset and the quest for the silver bullet for AUD, narcotic abuse, etc., that led to taking the pill the wrong way. Eventually the body would compensate for the constant high levels of Nal and the blockade of the opioid receptors would fail, while the habit/compulsion stayed intact. Additionally, selective extinction couldn't occur, so the unhealthy habit remained unchallenged by healthy habits.