Medication use during pregnancy has changed over time because of various factors: new products have been marketed, concerns have arisen regarding safety and efficacy, public education has increased, and some prescription medications have been granted nonprescription status by the Food and Drug Administration. The purpose of this investigation was to determine overall medication and substance use by prenatal patients whose infants were delivered at our tertiary university hospital. Within 96 hours after delivery, 100 women were evaluated by a personal interview and medical record review. The medications most commonly used during pregnancy were vitamins, analgesics, calcium and iron preparations, and antibiotics. The mean numbers of medications consumed during the second and third trimesters (3.32 +/- 1.87 and 4.13 +/- 2.46) were significantly higher than the mean number taken before pregnancy (2.65 +/- 1.95). Over-the-counter medications accounted for 54% of the total products taken during pregnancy. Percentages of women using caffeine, tobacco, alcohol, and illicit drugs decreased during pregnancy.