How many types of neurotransmitters are there in a human brain?

It depends on how you count, but maybe 30 - 100 different molecule types, with 10 of them doing 99% of the work. In the big scheme of things, there are three main categories of neurotransmitters: "Small molecule" neurotransmitters (glutamate, GABA, dopamine, serotonin, noradrenaline, acetylcholine, and histamine) Neuropeptides (endorphins, oxytocin, and possibly 100 more) Other (small molecules like nitric oxide, adenosine, ATP, glycine; or larger molecules like endocannabinoids) In terms of total number of neurotransmitters, maybe 10 small molecules (less than 30 atoms each) and 100+ neuropeptides (50 - 200 atoms each), with 20 or so neuropeptides getting most of the research attention. Related