Deadly nightshade's poison, atropine, became a nerve agent antidote
The same compound that makes deadly nightshade dangerous is carried by soldiers in autoinjectors to survive nerve gas. Atropine, first isolated in 1833 and now counted by the WHO among its essential medicines, works by blocking one of the body's main chemical messengers, which can save a life or, in excess, cause one to unravel.
The key is acetylcholine, the main signalling chemical of the parasympathetic nervous system, which handles rest-and-digest functions such as slowing the heart and producing saliva. Atropine sits in acetylcholine's muscarinic receptors without activating them, a competitive and reversible blockade. Nerve agents such as sarin and VX, and organophosphate insecticides, do the opposite: they destroy the enzyme that clears acetylcholine away, so the signal floods the body. Atropine blunts that overstimulation, and it is often paired with pralidoxime, which can undo the enzyme damage. Troops facing chemical attack carry both for rapid injection into the thigh.
The heart shows the effect clearly. Vagus nerves release acetylcholine onto the heart's natural pacemaker, keeping resting rates low, so blocking them speeds the heart and quickens conduction. That makes atropine useful in hospitals for certain dangerously slow rhythms, although it was dropped from cardiac arrest guidelines in 2010 for lack of evidence. Oddly, very small amounts can slow the heart instead, probably through effects in the brain.
In the eye, atropine dilates the pupil and temporarily paralyses focusing. It can take 7 to 14 days to wear off, so quicker drugs are preferred for routine eye exams. Blurring the stronger eye with atropine drops has proved as effective as an eye patch for some children with lazy eye, and low-strength drops slow worsening short-sightedness in children.
Too much produces a recognisable toxic picture: hot, dry, flushed skin, blurred vision, racing heart, confusion and hallucinations, since the drug crosses into the brain. Physostigmine or pilocarpine can reverse it. During the Cold War someone spiked cafeteria salt shakers with atropine in an attempt to poison staff at Radio Free Europe. The alkaloid occurs naturally in several nightshade relatives, including jimsonweed, mandrake and angel's trumpet.
Source: Atropine
