Which of the following drugs is not classified as an SSRI?

Duloxetine is not classified as a selective serotonin reuptake inhibitor (SSRI). Instead, it is categorized as a serotonin-norepinephrine reuptake inhibitor (SNRI). This classification reflects its mechanism of action, which involves the inhibition of the reuptake of both serotonin and norepinephrine, two neurotransmitters associated with mood regulation.

In contrast, citalopram, fluoxetine, and sertraline are all SSRIs. These drugs primarily function by selectively inhibiting the reuptake of serotonin in the brain, thus increasing its availability and enhancing mood. This differentiation between SSRIs and SNRIs is critical in understanding their therapeutic applications and potential side effects. Consequently, knowing the classifications and mechanisms helps in selecting the appropriate medication for treating various psychiatric conditions.