We can go even further beyond. This distinction is only wxclusive when we're talking about a living thing. When talking about the substances themselves, one is a subcategory of the other. A venomous snake is not poisonous, but a venomous venom is a poisonous poison.
The fact that we're having this discussion at all kind of proves that either English is losing the distinction, or it was never as clear a distinction as people sometimes make it out to be. Either way I'm fine with it because it doesn't seem like a very useful distinction to make in everyday language, and you can sidestep it entirely by using a word like toxic instead.