Diphenhydramine overdose during pregnancy: lessons from the past.

A primigravid woman was seen for the first time in a disoriented and combative state, with regular, painful uterine contractions. Evaluation revealed a negative illicit drug screen, no evidence of preeclampsia, and a nonfocal neurologic examination. Further workup revealed urinary diphenhydramine levels suggesting drug overdose. This case serves as a reminder of the oxytocin-like effects of diphenhydramine.