> Maybe a good basis for differentiating “drugs” vs “medicine”?
Perhaps, although I don't think in the way I'd take your statement. Chesterton was quite opposed to the idea that drinking would be medicinal (although maybe he would have allowed that happiness is good medicine?). From the context[1]:
> A new morality has burst upon us with some violence in connection with the problem of strong drink; and enthusiasts in the matter range from the man who is violently thrown out at 12.30, to the lady who smashes American bars with an axe. In these discussions it is almost always felt that one very wise and moderate position is to say that wine or such stuff should only be drunk as a medicine. With this I should venture to disagree with a peculiar ferocity. The one genuinely dangerous and immoral way of drinking wine is to drink it as a medicine. And for this reason, If a man drinks wine in order to obtain pleasure, he is trying to obtain something exceptional, something he does not expect every hour of the day, something which, unless he is a little insane, he will not try to get every hour of the day. But if a man drinks wine in order to obtain health, he is trying to get something natural; something, that is, that he ought not to be without; something that he may find it difficult to reconcile himself to being without. The man may not be seduced who has seen the ecstasy of being ecstatic; it is more dazzling to catch a glimpse of the ecstasy of being ordinary. If there were a magic ointment, and we took it to a strong man, and said, "This will enable you to jump off the Monument," doubtless he would jump off the Monument, but he would not jump off the Monument all day long to the delight of the City. But if we took it to a blind man, saying, "This will enable you to see," he would be under a heavier temptation. It would be hard for him not to rub it on his eyes whenever he heard the hoof of a noble horse or the birds singing at daybreak. It is easy to deny one's self festivity; it is difficult to deny one's self normality. Hence comes the fact which every doctor knows, that it is often perilous to give alcohol to the sick even when they need it. I need hardly say that I do not mean that I think the giving of alcohol to the sick for stimulus is necessarily unjustifiable. But I do mean that giving it to the healthy for fun is the proper use of it, and a great deal more consistent with health.
[1] https://www.gutenberg.org/files/470/470-h/470-h.htm (search for "Omar and the Sacred Vine" -- chapter 7).