Medications During Pregnancy: Safety, Risks & What to Know

Taking medications during pregnancy requires careful consideration — both undertreating a medical condition and taking a harmful drug can put mother and baby at risk [1]. Approximately 90% of pregnant women take at least one medication during pregnancy, and about 70% take at least one prescription drug [2]. Understanding the risks and how to navigate medication decisions during pregnancy is essential for every woman of childbearing age. How Medications Affect Pregnancy Most drugs can cross the placenta and reach the developing fetus [1][2]. The risk depends on the drug, the dose, the duration of exposure, and the timing during pregnancy. The first trimester (weeks 1-12) is the period of greatest risk for structural birth defects (teratogenicity) because this is when major organs are forming [2]. However, exposure during the second and third trimesters can also cause problems — growth restriction, functional abnormalities, premature labor, or neonatal withdrawal symptoms [1]. The FDA Labeling System In 2015, the FDA replaced the old pregnancy letter categories (A, B, C, D, X) with the Pregnancy and Lactation Labeling Rule (PLLR), which requires more detailed narrative descriptions of risk based on available human and animal data [1][3]. The new format includes three subsections: Pregnancy (including labor and delivery), Lactation, and Females and Males of Reproductive Potential. This system provides more nuanced information than the old letter categories but requires careful reading [3]. Medications Generally Considered Safe in Pregnancy While no drug can be considered absolutely safe in pregnancy, some medications have extensive human data supporting their use [1][2]. These include acetaminophen (Tylenol) for pain and fever, many penicillin and cephalosporin antibiotics, most prenatal vitamins, insulin for diabetes management, levothyroxine for thyroid replacement, and certain antihistamines (loratadine, cetirizine) for allergies. However, "generally safe" does not mean risk-free — always confirm with your OB/GYN before taking any medication [2]. Medications Known to Cause Birth Defects Some drugs are known teratogens and must be avoided in pregnancy [1][2]. These include isotretinoin (Accutane) — the most potent human teratogen in clinical use, causing severe birth defects in up to 35% of exposed pregnancies. Thalidomide and lenalidomide cause limb malformations. Valproic acid increases neural tube defect risk by 10-20 fold. Warfarin causes bone and cartilage abnormalities. Methotrexate is an abortifacient and teratogen. ACE inhibitors and ARBs can cause kidney damage and underdevelopment in the fetus, particularly in the second and third trimesters [2]. Lithium is associated with cardiac malformations (Ebstein anomaly), though the risk is lower than historically believed [4]. Making Medication Decisions During Pregnancy Never stop a prescribed medication abruptly when you discover you are pregnant — the risks of untreated conditions (epilepsy seizures, severe depression, uncontrolled diabetes, hypertension) may outweigh medication risks [1][2]. Contact your prescriber immediately to discuss the safest approach. For planned pregnancies, discuss medication adjustments with your doctor before conception — this allows time to switch to safer alternatives if needed [2]. Resources like MotherToBaby (mothertobaby.org), a service of the Organization of Teratology Information Specialists, provides evidence-based information about medication safety during pregnancy and breastfeeding [5]. Breastfeeding and Medications Most medications pass into breast milk in small amounts, but for many drugs the amount is too low to affect the infant [1]. The Lactation section of drug labeling and resources like LactMed (a free NIH database) provide specific guidance [6]. Generally, maternal medications that are safe include acetaminophen, ibuprofen, most antibiotics, insulin, and thyroid replacement. Drugs to avoid during breastfeeding include certain chemotherapy agents, ergot alkaloids, and some psychiatric medications — always check with your doctor and pediatrician [1][6].