A GABA agonist is a drug which acts to stimulate the GABA receptor, producing typically sedative effects, and may also cause other effects such as anxiolytic and muscle relaxant effects. There are three receptors of the gamma-aminobutyric acid. The two receptors GABA-α and GABA-ρ are ion channels that signal chloride and diminish further action potentials. The GABA-β receptor belongs to the class of G-Protein coupled receptors that inhibit adenylyl cyclase, therefore leading to decreased cyclic adenosine monophosphate (cAMP). GABA-α and GABA-ρ receptors produces sedative and hypnotic effects as well as producing anti-convulsion properties. GABA-β receptors also produce sedative effects and also leading to changes in gene transcription.
Contrary to popular misconception, many commonly used sedative and anxiolytic drugs that affect the GABA receptor complex aren't actually agonists. These drugs are known as positive allosteric modulators, and while they do bind to the GABA receptors, they cannot induce a response from the neuron without an actual agonist being present. Drugs that fall into this class exert their pharmacodynamic action by increasing the effects that an agonist has when potentiation is achieved.
Positive allosteric modulators work by increasing the frequency with which the chlorine channel opens when an agonist binds to its own site on the GABA receptor. The resulting increase in the concentration of Cl- ions in the postsynaptic neuron immediately hyperpolarizes this neuron, making it less excitable and thus inhibiting the possibility of an action-potential.