There are four major antidepressant classes. These medications primarily achieve their action by increasing which neurotransmitter in the CNS?

• A. Acetylcholine
• B. Dopamine
• C. Serotonin
• D. Norepinephrine

Answer: (C)

Antidepressants work mainly by boosting monoamine neurotransmitters in the brain to improve mood, and serotonin is the one most consistently increased by the major classes. SSRIs specifically inhibit the serotonin transporter, leaving more serotonin in the synaptic cleft. Other major antidepressants—like TCAs, SNRIs, and MAOIs—ultimately raise serotonin levels as well (through reuptake inhibition or by blocking breakdown), which is why serotonin is the key neurotransmitter linked to their therapeutic effect. While norepinephrine can also be increased by several of these drugs and dopamine may be affected by some, the common thread across the four main classes is an increase in serotonin. Acetylcholine is not a primary target of these antidepressants.