What is the primary action of a selective serotonin reuptake inhibitor (SSRI)?

The primary action of a selective serotonin reuptake inhibitor (SSRI) is to block serotonin reuptake. This mechanism enhances serotonin activity in the brain by preventing its reabsorption into the presynaptic neuron after it has been released into the synaptic cleft. As a result, more serotonin remains available to bind to postsynaptic receptors, which is believed to contribute to the alleviation of symptoms of depression and anxiety.

This pharmacological action is pivotal in treating various mood disorders, as serotonin is a key neurotransmitter involved in mood regulation. By increasing the levels of serotonin available in the synaptic cleft, SSRIs can help improve mood and reduce the overall symptoms of depression and anxiety disorders.