The D2 receptor occupancy reaches 85-94% at doses greater than which amount?

• A. >50 mg
• B. >125 mg
• C. >250 mg
• D. >500 mg

Answer: (B)

The main idea is that D2 receptor occupancy increases with the dose of an antipsychotic. When occupancy climbs into the high 80s to mid-90s percent, most available D2 receptors are blocked, which is typically linked to strong antipsychotic effects but also a higher risk of extrapyramidal symptoms. For the agent in this scenario, reaching that high level of occupancy occurs when the dose is around or above 125 mg. Below that, occupancy tends to be lower and may be subtherapeutic or carry a different side effect profile. Doses well above this threshold don’t substantially increase occupancy (since it’s near saturation) but do raise the risk of adverse motor effects, so they’re not desirable.