Which of the following is NOT an SSRI?

• A. Sertraline
• B. Fluoxetine
• C. Venlafaxine
• D. Citalopram

Answer: (C)

Understanding how SSRIs differ from SNRIs in their mechanism of action helps explain why venlafaxine is not an SSRI. SSRIs, like sertraline, fluoxetine, and citalopram, selectively block the serotonin transporter, increasing serotonin in the synaptic cleft with minimal effects on norepinephrine or dopamine at typical doses. Venlafaxine is an SNRI. It inhibits both the serotonin transporter and the norepinephrine transporter, boosting both serotonin and norepinephrine; at standard antidepressant doses its norepinephrine effect is significant, so it’s classified as an SNRI rather than an SSRI. Some sources note that very low doses can resemble SSRIs, but clinically it is an SNRI. Therefore, venlafaxine is not an SSRI.