Isn't Aspirin psychoactive in the same way? I.e. it takes away pain, which influences your psyche in an obvious way.

It's nit psychoactive in the sense that is has any direct perceptible effect on the brain. It reduces inflammation, which can be perceived as less pain indirectly altering your mental state.

Whereas psychoactive drugs generally affect the actual underlying processes in the brain through various interactions with receptor, enzymes, or neurotransmitters.

I hope that distinction makes sense.

You could argue that. there is no clear line of course, but most people would agree that a beer influences them more than aspirin or an antibiothic.

I see. To me, it is not very useful to talk about "psychoactive" substances, since sugar, caffeine, or nicotine are also "psychoactive". I would recommend the term "entheogens" in your original post.

Entheogen is even worse, that specifically means psychoactive drugs used for religious purposes. And guess what: nicotine is an entheogen!