 The study will compare effectiveness of intravenous magnesium sulfate to that of intravenous metoclopramide Reglan for acute headache in pregnant women. We will randomize pregnant women who present to our emergency department with chief complaint of headache to magnesium sulfate 2 grams intravenously or metoclopramide 10 mg intravenously; both groups will receive acetaminophen Tylenol 1 gram orally and normal saline 1 liter intravenously. Headaches are common during pregnancy, related to hormonal changes, altered sleep patterns and psychosocial stressors. Common medications for headache such as non-steroidal antiinflammatories or triptans are typically avoided during pregnancy due to concern for fetal effects. Women, and their physicians, are often uncertain regarding available medication options with justifiable safety profiles during pregnancy. 