Metoclopramide can cause side effects that include headache, drowsiness, fatigue, sleep problems, diarrhea, dizziness, constipation, and dry mouth. Contact a medical professional if you experience mood changes, restlessness, suicidal thoughts, urinary incontinence, and discharge from the nipples. Scopolamine, benztropine, and diphenhydramine (Benadryl) can block Reglan and make it ineffective. Do not take this medication with sleep drugs, psychiatric medications, antihistamines, MAO inhibitors, or drugs used to treat seizures.