Which class do SSRIs belong to?

• A. Serotonin-norepinephrine reuptake inhibitors
• B. Selective serotonin reuptake inhibitors
• C. Monoamine oxidase inhibitors
• D. Tricyclic antidepressants

Answer: (B)

SSRIs are defined by their mechanism: they selectively block the serotonin transporter (SERT), the protein that normally clears serotonin from the synaptic cleft. By inhibiting SERT, they increase serotonin levels in the synapse, enhancing serotonergic signaling with little impact on norepinephrine or dopamine at typical doses. This selective action on serotonin reuptake is why they are classified as selective serotonin reuptake inhibitors. Examples include fluoxetine, sertraline, citalopram, escitalopram, paroxetine, and fluvoxamine, commonly used for depression and anxiety disorders. In contrast, drugs that block reuptake of both serotonin and norepinephrine are serotonin-norepinephrine reuptake inhibitors; those that prevent breakdown of monoamines are monoamine oxidase inhibitors; and tricyclic antidepressants block reuptake of serotonin and norepinephrine but also affect other receptors, leading to more side effects and less receptor selectivity.