Brexpiprazole is best described as which of the following?

• A. Partial agonist for 5-HT1A, D2, D3; high affinity for D2 and D3
• B. Full antagonist at D2
• C. Partial agonist at 5-HT2A only
• D. No receptor activity

Answer: (A)

Brexpiprazole works by dialing down dopamine and tuning serotonin signaling rather than simply blocking receptors. It acts as a partial agonist at dopamine D2 receptors and at D3 receptors, and also as a partial agonist at serotonin 5-HT1A receptors, with particularly high affinity for D2 and D3. This means it can dampen excessive dopaminergic activity related to psychosis while preserving some dopaminergic tone to reduce movement-related side effects, and the 5-HT1A activity adds potential antidepressant/anxiolytic benefits. It also has 5-HT2A antagonism, which complements its antipsychotic effects, but the key descriptor is the partial agonism at D2, D3, and 5-HT1A with high D2/D3 affinity. The other options describe full antagonism, limited receptor activity, or no receptor activity, which don’t fit brexpiprazole’s pharmacology.