Ms. A was a 19-year-old white woman with mild mental retardation and a history of birth anoxia. She was referred to us after 4 years of emotional instability, with periods of depression or agitation and heightened activity, both marked by poorly formed delusions. No health problems were reported; there were no reports of recreational drug or alcohol use. Ms. A’s mother—who accompanied her on every visit—and her special school were dissatisfied with her response to her current medication regimen, which included 15 mg of olanzapine at bedtime and 250 mg b.i.d. of divalproex. Ms. A’s mother stated that her daughter was restless and inattentive but also sedated. Her mother also stated that Ms. A had a slight milky breast discharge that she believed had appeared approximately 3 weeks after olanzapine treatment had begun. Ms. A was an extremely poor reporter of events and of her internal states. The results of laboratory tests were all normal, including a normal level of thyroid-stimulating hormone and a prolactin measurement of 13 ng/ml (normal range=3–30). Ms. A’s serum valproate level was 64 μg/ml. Mild to moderate akathisia was noted.

Ms. A was switched from olanzapine to 100 mg of quetiapine in the morning and 300 mg at bedtime, and her divalproex dose was increased to 750 mg/day. After 4 weeks, no akathisia was observed or reported, and Ms. A’s mother reported that the breast discharge had ceased. A repeat prolactin measurement revealed a serum level of 5 ng/ml and a valproate level of 114 μg/ml. Ms. A’s mother and her school reported significant behavioral improvements that continued for over 1 year of follow-up without the return of side effects. Since Ms. A’s prolactin level was normal and the galactorrhea had stopped after quetiapine was discontinued, no further workup was undertaken.