Which statement is true regarding the olanzapine and carbamazepine interaction?

• A. It reduces olanzapine by 36-71%
• B. It increases olanzapine by 30%
• C. It has no effect
• D. It reduces olanzapine by 80%

Answer: (A)

When carbamazepine is taken with olanzapine, carbamazepine acts as a strong inducer of hepatic enzymes that metabolize olanzapine, speeding its clearance from the body. Olanzapine is mainly cleared by CYP1A2 and other enzymes, so this induction lowers olanzapine exposure in most people. Clinically, this reduction in olanzapine levels is commonly in the range of about 36% to 71%, which can lessen therapeutic effect and may necessitate dose adjustments or choosing another agent. The idea that levels would rise, that there’s no effect, or that the drop would be 80% is not consistent with typical pharmacokinetic data for this interaction.