Acetylcholine
Acetylcholine (C7H16NO2) was a neurotransmitter found in the autonomic nervous system of most humanoid brains. 

It played a role in promoting aggressive tendencies. () The reduction of acetylcholine levels could help level off neurotransmitter levels and the stabilization of motor neurons. ()

When the crew of  was possessed by Wisps, the possessed state was characterized by elevated acetylcholine levels in the autonomic nervous system. ()

Spock performed an acetylcholine test on a huge spaceborne amoeba creature that destroyed the Gamma 7A system in 2268, although McCoy felt the test was botched. () 

As a choline compound, acetylcholine could be used to stabilize synapses in cases of nervous system collapse. However, it was not effective against the effects of an alien weapon that killed  Ensign Ahni Jetal. ()

When acetylcholine absorption was stimulated, it increased tensile strength of the muscle tissue. This was done during a neuromuscular adaptation treatment. ()

An increase of acetylcholine within the hippocampus could indicate that the person had accumulated memories. A thirteen percent increase would indicate an accumulation of two days' worth of memories. ()

The Akritirian clamp stimulates the production of acetylcholine in the hypothalamus, causing irritation and aggression. ()

When Neelix was resurrected with Borg nanoprobes in 2374, The Doctor reduced his acetylcholine levels in an attempt to stabilize his motor neurons. ()

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Biochemical compounds