I've read that when a person becomes addicted to something, the substance in question actually hijacks the pleasure centers of the brain, such that the addictive substance becomes the person's main, if not only, source of pleasure.
If a person stays sober long enough, the brain can gradually rewire itself to where it's possible to feel pleasure "normally," but the cravings can become incredibly strong in the meantime. And every time someone "falls off the wagon," the process has to start all over again. I suspect that's why relapses are so common and why there are so many people who have a really hard time achieving long term sobriety.
That is my admittedly limited layperson's understanding of the matter, but it makes a lot of sense to me. I know even less about naltrexone, but it sounds like the drug may be helping with the rewiring of the pleasure centers, providing something that allows the brain to function more notmally without the drug of choice sooner than it would be able to otherwise, or both. Or maybe something else altogether, but whatever it is, it works, and it sounds like something close to a miracle to me.
I wish it had come along in time for my alcoholic dad. He found AA to be helpful and was on the wagon most of the time while I was growing up, but every so often life would get to be a little too much, he'd succumb to the siren call of a frosty class of beer, and boom, there he was in relapse land. After which he would beat himself up for his "lack of self control."
I'll bet naltrexone could have helped him a lot. It's too late for him, but I'm glad it's there for alcoholics and other addicts now, and I hope it gets wider and wider use, because it sounds amazing.