Dopamine, norepinephrine, and serotonin are probably the best known of the neurotransmitters and the ones most frequently targeted by psychiatric medication. All three are classified as monoamines based on their chemical structure. Glutamate is a general excitatory neurotransmitter—it increases the likelihood that neurons will fire. GABA is a general inhibitory neurotransmitter—it decreases the likelihood of neurons firing. Histamine is known for its involvement in the allergic response. Acetylcholine is involved with memory and is targeted by anti-Alzheimer’s drugs.