[Dilantin toxicity as a possible cause of major depression].

Diphenylhydantoin (D; Dilantin) is widely used in neurologic and psychiatric practice for treating convulsive disorders. D overdosage and poisoning may cause behavioral disturbances, such as schizophreniform and delusional states. To the best of our knowledge, D has been linked with mood disorders in just 1 documented case. We report a 70-year-old woman who developed major depression as a complication of D intoxication. Treatment with folic acid led to complete recovery. We believe that D causes depression by lowering folic acid blood levels by a biochemical mechanism. We suggest that levels of D and folic acid be monitored continually all patients treated with the drug.