Monoamine oxidase A (MAOA) is an enzyme involved in the metabolism of the monoamines, eg 5-HT and noradrenaline. It converts the monoamines into their corresponding carboxylic acid via an aldehyde intermediate. MAOA regulates both the free intraneuronal concentration and the releasable stores of 5-HT and noradrenaline. MAOA inhibitors bind to and inhibit MAOA, preventing monoamine degradation. This results in greater stores of monoamines available for release. MAOA inhibitors are used in the treatment of depression. It has been proposed that MAO inhibitors treat depression by preventing monoamine degrdation and delaying downregulation of beta-andrenoceptors and 5-HT2 receptors.