Background: Medication use during pregnancy and lactation can be unavoidable, but knowledge on safety for the fetus or breastfed infant is limited among patients and healthcare providers. Research aim: This study aimed to determine (a) the prevalence of medication use in pregnant and lactating women in a tertiary academic center, (b) the types and safety of these medicines, and (c) the influence of medication use on initiation of breastfeeding. Methods: This study used a cross-sectional survey among women (N = 292) who underwent high-risk or low-risk deliveries. Data about their use of prescribed, over-the-counter, and homeopathic medication during pregnancy were obtained through a structured interview, followed by a questionnaire during lactation. Safety was classified according to the risk classification system from the Dutch Teratological Information Service. Results: Overall, 95.5% of participants used medication. One third of participants used at least one medicine with an unknown risk for the fetus. Teratogenic medication was used by 6.5% of participants, whereas 29.5% used medication with a (suspected) pharmacological effect on the fetus. Lactation was initiated by 258 (88.7%) participants, of which 84.2% used medication while breastfeeding. In 3.8% of participants, this medication was classified unsafe, but none used medication with an unknown risk. One-third of the nonlactating participants decided not to initiate breastfeeding because of medication use. In 70% of participants, this decision was appropriate. Conclusion: The prevalence of overall use of medication in Dutch pregnant and lactating women admitted to a tertiary center was high. There is an urgent need for pharmacometric studies for determination of the safe use of the most frequently used medicines during pregnancy or lactation.