Great question, Lonewarrior. So, the nerve cell, having its receptors blocked by naltrexone, "feels" deprived of the neurotransmitter, and so puts out more receptors for them, so that next time, it will be more sensitive to the endorphins. That is up-regulation. Before I heard about TSM, I had heard about LDN - low dose naltrexone. Not for help with alcohol, but used for a way of improving mood, perhaps in depression. The idea, as I understand it, is to temporarily deprive your neurons of endorphins or endogenous opiates during the night with very small doses of naltrexone while you were asleep, so your nerve cells would up-regulate their receptors. Then, during the day, one would theoretically enjoy a higher sensitivity to these neurotransmitters or hormones... I don't have any experience with it, but an interesting theory! I am a newbie here, but I do wonder what role this plays in TSM. And what it has to do with something as complex as sex I really don't venture to speculate!
So - back to your question: I think you don't want to block your receptors entirely. Only when you have alcohol on board. So you take it when you drink, and allow it to wear off, probably during the day when you are not going to drink anyway. So the receptors don't bloom too much. This up-regulation might be, I think, one of the reasons you really don't want to drink without the naltrexone. Again, I'm new to this, but it makes sense to me.
So guess what happens when, before naltrexone, we drink for extended periods day after day - we get "down-regulation". That's why we feel shaky when we stop. The nerve cells, accustomed to alcohol, have decreased their sensitivity to it, and then when you stop drinking, they really are missing the calming effect of alcohol, and fire too readily. They become too sensitive, too irritable, so normal sounds are too loud, normal light hurts your eyes, etc. Of course this is oversimplified, and alcohol, unlike opioids and endorphin, does not actually need receptors to get into a cell, it is a small molecule that easily goes everywhere. The concept is the same.
This down-regulaton of receptors is exactly what does happen with tolerance to narcotics, for example, so people with chronic pain who take narcotics every day need higher and higher doses.