system
Given the following post, respond as if you're commenting on Reddit:
human
Why some south american plants produce curare alkaloids, if those alkaloids are not absorbed via GI route and are only effective via parenteral injection?
gpt
Alkaloids are most commonly produced to protect the plant from parasites or animals eating the plant, but can have other roles as well (it's not a well settled question, in part because there are a LOT of different alkaloids).

It's not uncommon for alkaloids to have very different effects depending on what species ingests them - we see this with cocoa, for example, which is fine for human consumption but poison for cats and dogs.

I don't know the original biological role of curare alkaloids, but it's possible the organisms they're protecting against do not have the same barrier we do in the GI tract preventing the poison from entering the body (into the blood or hemolymph or whatever is relevant for the organism). Or the plant may just be relying on the alkaloid tasting bad, even if it isn't actually poisonous for the animals.