Which of the following is an SSRI?

• A. Diazepam
• B. Venlafaxine
• C. Fluoxetine
• D. Amitriptyline

Answer: (C)

The key idea is recognizing drugs that specifically increase serotonin by blocking its reuptake, a category known as SSRIs. Fluoxetine fits this description because it selectively inhibits the serotonin transporter (SERT), preventing reabsorption of serotonin into the presynaptic neuron. This leads to higher serotonin levels in the synaptic cleft, which is the hallmark of SSRI action and is how these drugs help alleviate depressive and anxiety symptoms.

Diazepam, in contrast, is a benzodiazepine that enhances the effect of GABA on the GABA-A receptor, producing sedation and anxiolysis through a different neurotransmitter system, not serotonin reuptake inhibition.

Venlafaxine operates as an SNRI, meaning it inhibits the reuptake of both serotonin and norepinephrine, with its SNRI activity becoming more pronounced at higher doses. It’s not classified as an SSRI.

Amitriptyline is a tricyclic antidepressant that also blocks reuptake of serotonin and norepinephrine but affects other receptors as well, leading to a broader, less selective profile than SSRIs.