If you abused any stims that make you lose weight a lot, dropping them usually pushes your bodyweight in the other direction. Know a few people like this. They always relapse
That is cultural. It’s poison you take to change your mind state and small enough amounts are usually tolerable enough to not cause too much of a problem. I have a drink from time to time but to say otherwise is incorrect.
Ok now put it in context to this conversation. The post said he gained weight after he became sober from "drug abuse". You said it is unlikely to gain weight when you quit abusing alcohol. So therefore... He was not abusing alcohol but some other drug that has a side effect of weight loss. You're welcome, now you can continue not using your brain.