An agonist for the neurotransmitter gamma-aminobutyric acid (GABA). GABA is a major inhibitory neurotransmitter. In mammals, GABA-containing neurons and receptors are found in the Central Nervous System; while in arthropods and nematodes GABA is found primarily in the Peripheral Nervous System (neuromuscular junction). This difference in location of GABA receptor may be the reason for the large margin of safety of ivermectin-containing products in mammals [my emphasis]. The binding of ivermectin to a neuronal membrane increases the release of GABA. GABA binds to the GABA receptor-chloride channel complex of postsynaptic neuronal membranes causing an influx of chloride ions. The influx of chloride ions hyperpolarize the neuronal membrane making them less excitatory and decreasing nerve transmission. The hyperpolarization of neuronal membranes (at the NMJ) mediate a flaccid paralysis in arthropods and nematodes.