Why do so many plants produce chemicals that mimic neurotransmitters?

Question

Is this a coincidence?

Answer 1

Not mere neurotransmitters but most other drugs that act on humans and animals are derived from plants. It is nature`s way of keeping plants,animals humans useful to each other and safe from one another.

Answer 2

often they are self-defense drugs that allowed the plant at one-time or another better fight off predators. Many plants that get humans high will kill smaller, differently wired predators.

Also there are not many that actually mimic neurotransmitters--the only one i can think of is Glutamate (One part of of MSG, (other is salt or sodium) and what largely makes soup and meat taste so good) which is a simple amino acid and therefore nothing special. Usually they mimic instead human hormones - Caffeine, THC, LSD, Peyote, and amphetamines are interpreted (i.e. similar) as hormones in the body. One of the interesting problems of long-term addiction is that the receptors of these HORMONES adapt to the similar but not identical plant products and become less-sensitive to the actual, self-produced one. Opiates are a little different but they are still not the neuro-transmitter its-self, they only interfere with a enzyme's (protein) ability to break down the neurotransmitter it the usual fashion.