Comment by rex_lupi

They are not "natural" in the sense that humans don't consume ethyl alcohol to survive, in fact it is often quite damaging to biological systems. Apart from some microbes I'm not aware of any other organisms that use alcohol as their energy source. Alcohol/thc/caffeine/nicotine (you name it) do not fall in the "natural" diet of humans. Most psychoactive substances are metabolites which plants/fungi store in them to deter other animals from eating them.