Whether they meant to do it or simply ingested it..
Amanita mushroom, AKA the fly agaric, is both hallucinogenic and poisonous. It's used in small doses to induce vivid and intense dreams. Amanita muscaria is legal in North America.
Mandrake is a real plant. It's toxic in higher doses and powerfully deliriant in lower doses. Learn about the strange world of the mandrake root.