One of the most toxic plants in the world, the deadly nightshade (Atropa belladonna) is filled with tropane alkaloids, which can kill an adult in large enough doses. Its primary active agent, atropine, attacks the parasympathetic nervous system and disrupts its ability to regulate subconscious activities like breathing.
Considering its lethality, it may come as a surprise that scientists have found beneficial uses for atropine in medicine. When used as an acetylcholine receptor blocker to curb the activity of overactive neurons, it helps to negate the deadly effects of nerve agents like sarin and anthrax, which cause victims to lose control of their bodily functions. Atropine is also used to treat glaucoma and to resuscitate patients suffering from cardiac arrest.