Serotonergic () or serotoninergic () means "pertaining to or affecting serotonin". Serotonin is a neurotransmitter. A synapse is serotonergic if it uses serotonin as its neurotransmitter. A serotonergic neuron produces serotonin. A substance is serotonergic if it produces its effects via interactions with the serotonin system, such as by stimulating or blocking neurotransmission.