What is the primary mechanism of action of serotonin-norepinephrine reuptake inhibitors (SNRIs)?

• A. Block D2 receptors
• B. Inhibit reuptake of serotonin and norepinephrine
• C. Inhibit acetylcholine
• D. Activate GABA receptors

Answer: (B)

SNRIs work by blocking the presynaptic transporters for both serotonin and norepinephrine, so these neurotransmitters are cleared from the synapse more slowly. That keeps higher levels of serotonin and norepinephrine available to bind receptors, boosting signaling in mood-regulating circuits in the brain. This explains why these drugs help alleviate depressive and anxiety symptoms. It also explains why the other options aren’t the mechanism: blocking D2 receptors relates to antipsychotics, inhibiting acetylcholine would produce anticholinergic effects, and activating GABA receptors is how some sedative-hypnotics and anticonvulsants work. Common SNRIs include venlafaxine and duloxetine, among others, whose clinical effects stem from this increased monoamine signaling.