What drugs can cause miscarriage and birth defects?

October 7, 2025 •

6 min read

It is estimated that up to 25% of all recognized pregnancies end in miscarriage, with various factors contributing to this outcome. A critical factor for fetal health is medication exposure, and understanding what drugs can cause miscarriage and birth defects is paramount for expectant parents.

Quick Summary

Certain medications, including specific antibiotics, acne treatments, anticoagulants, and mood stabilizers, pose a risk to a developing fetus. The potential for miscarriage or birth defects depends on the drug, dosage, and timing of exposure, underscoring the importance of medical consultation.

Key Points

Isotretinoin is a High-Risk Teratogen: Used for severe acne, this drug carries a very high risk of causing severe birth defects and must be managed under strict risk programs for women of childbearing age.
Timing of Exposure is Crucial: The first trimester is the most sensitive period for major birth defects due to organ formation, but medications can cause problems throughout pregnancy.
Common OTC Medications Can Be Dangerous: NSAIDs like ibuprofen can increase the risk of miscarriage in early pregnancy and cause heart/kidney issues later on, making acetaminophen the generally safer alternative for pain.
Illicit Drugs Pose Severe Threats: Substances like cocaine and opioids are consistently linked to miscarriage, preterm birth, low birth weight, and neonatal withdrawal.
Warfarin Requires Careful Management: The anticoagulant warfarin can cause fetal skeletal abnormalities and CNS damage, especially in the first trimester, necessitating a switch to safer options like heparin.
Never Stop Prescribed Medication Abruptly: For chronic conditions like epilepsy or bipolar disorder, suddenly stopping medication can be more dangerous than continuing it. Any changes must be made with a doctor's supervision.
Consult a Healthcare Provider for All Medications: This includes over-the-counter drugs, herbal supplements, and vitamins. Always inform any prescribing doctor that you are pregnant or trying to conceive.

Understanding Teratogens and Pregnancy Risk

A teratogen is any agent that can disrupt the normal development of an embryo or fetus, leading to birth defects or other fetal abnormalities. The risk of harm from a teratogen depends heavily on the timing of exposure during pregnancy. The first trimester is particularly vulnerable because it is the period of organogenesis, when the fetus's major organs and systems are forming. However, exposure later in pregnancy can also cause problems, such as developmental delays, growth restriction, or damage to specific organs.

Recognizing the need for clearer information, the U.S. Food and Drug Administration (FDA) in 2015 replaced its letter-based (A, B, C, D, X) pregnancy risk categories with the Pregnancy and Lactation Labeling Rule (PLLR). The PLLR provides more detailed information on a drug's effects during pregnancy, lactation, and in individuals of reproductive potential. This change helps healthcare providers and patients make more informed decisions by offering a narrative summary of the known risks.

Prescription Medications with Known Risks

Acne Medications

Isotretinoin, a retinoid used to treat severe acne, is one of the most potent teratogens known. Exposure during pregnancy carries a high risk of spontaneous abortion and severe birth defects affecting the head, heart, and central nervous system. Due to this risk, women of childbearing potential taking isotretinoin must participate in a risk management program that includes pregnancy testing and reliable contraception. High doses of Vitamin A, also a retinoid, can also have teratogenic effects.

Anticoagulants

Warfarin, a blood-thinning medication, is known to be teratogenic, especially during the first trimester (weeks 6-9). Fetal warfarin syndrome can result in nasal hypoplasia and skeletal abnormalities. Use later in pregnancy is associated with central nervous system malformations. Safer alternatives, such as heparin, are typically used during pregnancy.

Anticonvulsants

Several older and newer antiepileptic drugs (AEDs) are associated with birth defects.

Valproic acid (Depakote, Depakene): Poses a significant risk of neural tube defects (e.g., spina bifida), cardiac anomalies, and developmental delay.
Carbamazepine (Tegretol): Associated with craniofacial defects, growth retardation, and potential cognitive effects.
Phenytoin (Dilantin): Linked to Fetal Hydantoin Syndrome, which can cause growth deficiencies, mental retardation, and facial anomalies.
Topiramate (Topamax): Associated with an increased risk of oral clefts. It is crucial for women with epilepsy to consult their doctor to manage their condition safely before and during pregnancy.

Blood Pressure Medications

ACE inhibitors (e.g., lisinopril, enalapril) and angiotensin II receptor antagonists (ARBs) carry significant risks when used in the second and third trimesters. They can cause severe fetal kidney problems, skull malformations, reduced amniotic fluid (oligohydramnios), and other complications. Discontinuation is recommended as soon as pregnancy is confirmed.

Psychotropic Medications

Lithium (for bipolar disorder): Associated with an increased risk of Ebstein's anomaly, a rare heart defect. However, the absolute risk is low and decisions about use must weigh the risks and benefits.
Benzodiazepines (e.g., Xanax, Valium): Some studies suggest a potential link to a slightly increased risk of oral clefts, while others find no significant association. Chronic use late in pregnancy can cause withdrawal symptoms in the newborn.
Antidepressants (SSRIs): Some SSRIs have been linked to potential, though debated, risks such as cardiac malformations and persistent pulmonary hypertension in newborns. The decision to continue or stop is made with a doctor based on the mother's mental health needs.

Antibiotics and Antimicrobials

While some antibiotics are safe, others carry risks.

Tetracyclines: Avoided due to potential for bone growth suppression and permanent tooth discoloration.
Streptomycin and Kanamycin (Aminoglycosides): Can cause fetal ear damage, leading to congenital deafness.
Quinolones and Macrolides (excluding erythromycin): Studies suggest some, like azithromycin and norfloxacin, may be associated with an increased risk of miscarriage in early pregnancy, though causal links are not fully established.
Sulfonamides: Risk of kernicterus (a type of brain damage) if used close to delivery.

Over-the-Counter (OTC) and Illicit Substances

Non-Steroidal Anti-Inflammatory Drugs (NSAIDs)

Common NSAIDs like ibuprofen (Advil, Motrin) and naproxen (Aleve) should be used with caution. Research indicates a potential increased risk of miscarriage when used early in pregnancy, especially around conception or for prolonged periods. After 20 weeks, NSAIDs can cause rare but serious fetal kidney problems and low amniotic fluid. Acetaminophen (Tylenol) is generally considered a safer choice for pain and fever relief.

Illicit Drugs

Illegal or street drugs are consistently linked to negative pregnancy outcomes.

Cocaine: Increased risk of miscarriage, preterm birth, restricted growth, and birth defects affecting the brain, heart, and urinary system.
Opioids (e.g., heroin, misused prescriptions): Can lead to miscarriage, poor fetal growth, preterm delivery, and neonatal abstinence syndrome (withdrawal) in the newborn.

Alcohol

There is no known safe amount of alcohol during pregnancy. Consumption can lead to Fetal Alcohol Spectrum Disorders, with the most severe cases resulting in Fetal Alcohol Syndrome, characterized by growth deficiencies, facial abnormalities, and developmental delays. Alcohol can also increase the risk of miscarriage.

Comparison of Pregnancy Risks by Drug Class


Drug Class	Key Teratogenic Risk	Gestational Risk Period	Safer Alternatives (Consult Doctor)
Retinoids (e.g., Isotretinoin)	Spontaneous abortion, severe birth defects	Throughout pregnancy (especially 1st trimester)	Topical retinoids (some), alternative acne treatments
Anticoagulants (e.g., Warfarin)	Skeletal/CNS malformations, intracranial hemorrhage	1st and 3rd trimesters	Heparin
Anticonvulsants (e.g., Valproic Acid)	Neural tube defects, cardiac anomalies	First trimester	Safer AEDs (e.g., Lamotrigine) or dose adjustment
ACE Inhibitors	Fetal kidney failure, oligohydramnios, skull defects	2nd and 3rd trimesters	Other hypertension medications (consult specialist)
Lithium	Ebstein's anomaly (rare heart defect)	First trimester	Careful risk/benefit analysis, specialist supervision
NSAIDs (e.g., Ibuprofen)	Miscarriage (early pregnancy), fetal kidney issues (late pregnancy)	First and Third Trimesters	Acetaminophen
Tetracyclines	Tooth discoloration, bone growth suppression	Throughout pregnancy	Penicillins, Cephalosporins
Alcohol	Fetal Alcohol Syndrome, miscarriage	Throughout pregnancy	Complete avoidance

Navigating Medication During Pregnancy

For anyone who is pregnant, planning to become pregnant, or breastfeeding, managing medication requires careful consideration. A proactive and informed approach is key to protecting both maternal and fetal health.

Plan Ahead: If possible, discuss your current medications with a healthcare provider before trying to conceive. They can review your needs, adjust dosages, or switch you to safer alternatives.
Never Stop Suddenly: Do not stop a prescribed medication for a chronic condition (e.g., epilepsy, depression) without consulting your doctor. The risks of an uncontrolled medical condition can sometimes outweigh the risks of the medication.
Consult Before Taking Anything: Always talk to your doctor, midwife, or pharmacist before taking any new medication, including over-the-counter (OTC) drugs, herbal remedies, or supplements.
Be Aware of OTC Risks: Even common OTC items like NSAIDs can carry risks. Check labels carefully and ask for advice.
Use Authoritative Resources: For questions about specific medications, consult reliable sources like the CDC or MotherToBaby.
Keep a Record: Maintain a record of all medications, supplements, and vitamins you take.

Conclusion

The question of what drugs can cause miscarriage and birth defects is complex, with risks varying significantly based on the substance, dosage, and timing of exposure. While it is important to be aware of the potential dangers associated with certain medications—from prescription drugs for chronic conditions to common OTC pain relievers and illicit substances—it is equally important to remember that not all medications are harmful. The key to ensuring a healthy pregnancy is to maintain open communication with your healthcare provider. Through careful planning and professional guidance, expectant parents can navigate their treatment options safely and minimize risks to their baby's development. Always prioritize consultation with a medical professional before making any changes to your medication regimen.

Visit MotherToBaby to speak with experts about the safety of medications and other exposures during pregnancy.

Frequently Asked Questions

While many antibiotics, like penicillins and cephalosporins, are considered safe for use during pregnancy, some types carry a higher risk. Studies have linked certain antibiotics, such as quinolones and some macrolides (e.g., azithromycin), to an increased risk of miscarriage, especially in early pregnancy. It is essential to discuss any need for antibiotics with a doctor to choose the safest option.

NSAIDs like ibuprofen and naproxen should generally be avoided during pregnancy. Research suggests they can increase the risk of miscarriage in the first trimester and cause serious heart and kidney problems for the fetus in the third trimester. Acetaminophen is a safer alternative for pain and fever, but it should still be used under medical guidance.

A teratogen is any substance or agent that can cause birth defects in an embryo or fetus. The first trimester is the most sensitive period because it is when all the major organs and body systems are developing (a process called organogenesis). Exposure to a teratogen during this time can cause severe structural malformations.

Fetal Alcohol Syndrome is a severe condition that can result from a mother's alcohol consumption during pregnancy. It is characterized by physical abnormalities, facial deformities, growth deficiencies, and problems with the central nervous system, including intellectual disabilities and behavioral issues.

If you discover you are pregnant while on a medication, the first step is to contact your doctor immediately. Do not stop taking any prescribed medication abruptly without consulting a healthcare professional, as this could cause harm. Your doctor can help you weigh the risks and benefits and decide on the safest course of action.

Illicit drugs, including cocaine, opioids, and marijuana, are often highly dangerous during pregnancy due to uncontrolled dosages and potential contaminants. However, certain prescription drugs are also classified as potent teratogens. The safest approach is to avoid all unprescribed and illicit drugs and to discuss all prescription medications with a healthcare provider.

Many herbal remedies and supplements are not regulated by the FDA and have not been adequately studied for safety during pregnancy. Some, like black cohosh or St. John's Wort, are known or suspected to be harmful. Always consult your healthcare provider before taking any herbal product or supplement.