Selective serotonin reuptake inhibitors (SSRIs) are a class of commonly used antidepressants, including fluoxetine, paroxetine, and sertraline. They work by selectively inhibiting the serotonin transporter protein (SERT) on neurons, preventing the reuptake of serotonin and increasing the concentration of serotonin in the synaptic cleft, thereby improving mood and depressive symptoms. SSRIs primarily act in the central nervous system, particularly affecting the brain's emotion regulation regions. They participate in multiple signaling pathways, regulating physiological processes such as mood, cognition, and sleep. Individual responses to SSRIs and their tolerability may be influenced by genetic differences, such as polymorphisms in the SERT gene.