Psychedelic mushroom
Psilocybin can kill in extremely high doses. The LD50 of psilocybin is 280 mg/kg for rats, this is about 1.5 times that of caffeine. In normal psychedelic mushrooms, psilocybin makes up about 1% of their weight. Therefore, nearly 1.7 kilograms of dried mushrooms, or 17 kilograms of fresh mushrooms, would be required for a 60 kg person to reach the 280 mg/kg LD50 rate of rats.