Penicillin is indeed the only in the group not to be plant-based. It comes from a mould (fungus) with antibacterial propertis, as observed by Fleming in the distant 1928. https://en.m.wikipedia.org/wiki/Penicillium
Warfarin is found in sweet clovers. Its story is really fascinating; I recommend having a look at this video on the topic . For hardcore people who're into pharm, the story is also reported on Goodman & Gilman. https://tube.cadence.moe/watch?v=OnzF0oJkYe0
People routinely eat poisonous herbs. Fennel is a great example.
But when my grandfather was in his 90s and taking Warfarin, every time my aunt saw the pill bottle, she would say (referring to her days in the Peace Corps), "that's what we used to kill rats in Kenya!"
"I appreciate SDF but it's a general-purpose server and the name doesn't make it obvious that it's about art." - Eugen Rochko