Unlike neurotransmitters which are synthesized at the synaptic terminal, neuroactive peptides are manufactured in the cell body through protein synthesis and transported down the axon to the synaptic terminal. Neuroactive peptides typically also have a longer period of activity than neurotransmitters.

Neuroactive peptides include many peptides that act as hormones elsewhere such as VIP, cholecystokinin, insulin, vasopresin, oxytocin. Additional neuroactive peptides include the endorphins and enkephalins as well as substance 16.