Unfortunately, knowledge of how acetylcholine works in the body has been used to cause harm.

Nerve gases, such as sarin, and pesticides inhibit acetylcholinesterase, the enzyme that breaks down acetylcholine. A buildup of acetylcholine in the synapse paralyzes muscles, which can lead to death.

One type of spider causes harm to humans in a unique way. The venom from the bite of a black widow spider dramatically raises the acetylcholine level causing severe muscle contractions, spasms, paralysis and possible death.