Do some plants have medicinal powers because we evolved with them (meaning we are just reinventing what we already knew for thousands of years), or is it more a random phenomenon?
So it’s not unreasonable that other plants may have also developed specific chemicals in response to some pressure from animals.
Though in a twist it turns out that one specific mammal has spread hot peppers far more than any birds ever before.
Wouldn't it make most sense for plants to develop chemicals that kill us, rather than cure us from a disease?
Take caffeine for example, likely it evolved as a defense against pests.
At higher concentrations yeah it’s an insecticide.
On the other hand, some plants do kill us.
Among the most interesting of plant responses is plant latex. Latex is found in lettuce, thistles, rubber, fig, and variety of other plants. Latex is thick with a variety of anti-microbial chemicals to ward off fungus, viruses, bacteria, insects, and more. These chemicals provide a wide distribution of medicinal value. Opium is a plant latex.
Have you considered why Australia has the most poisonous animals on the planet? Many venoms found there can easily kill humans many times over. It is supremely excessive, for humans, but not for the other animals living there. It is a constant state of evolving bio-chemical warfare because the intended victims evolve resistances to the strong venoms until they no longer become strong, so the predators and insects continually develop more targeted venoms to keep up.