“Alcohol is a mild poison” has been a house rule within my extended roleplaying circles for a long time. It fits well into almost any setting or metaphysics, and allows you to do interesting things with intoxication.
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...... it actually is though? its even defined as such in medical texts I've read.
Oh yes, although with roleplaying setting metaphysics, it's probably good to define this to be true if you're using it in your game. (To make sure it interacts with the rules correctly and has the right keywords etc etc.)
For example if you cast "detect poison" do you detect bottles of alcohol, or a hidden wine cellar, etc etc. If your DM has never considered whether or not alcohol is a poison it probably wouldn't occur to them to mention it, but if they have then they might!
Hmmm. It's often said that the difference between medicine and poison is a matter of dosage.
Which means that you could potentially use lesser restoration to kill someone who is receiving mundane treatments for a lethal disease.
Or, heck, consumed in sufficiently large doses, even water can be toxic.
That relationship is why in every edition but fifth, healing is necromancy, and why Heal and Harm are identical in 3rd/pf, because they're the same fundamentally, you just had to tweak the settings on one to get the other.