Which drug is unsafe in pregnancy? A Comprehensive Medication Guide

October 10, 2025 •

4 min read

According to the CDC, almost all pregnant women face decisions about taking medications during pregnancy. Knowing which drug is unsafe in pregnancy? is critical for protecting fetal health, as some substances can cause severe birth defects or complications, especially during the crucial first trimester.

Quick Summary

Identifying unsafe medications during pregnancy is vital for fetal health. This guide covers teratogenic drugs, over-the-counter medications, and lifestyle substances to avoid, and emphasizes consulting your provider for safer alternatives.

Key Points

Consult a Doctor First: Always speak with your healthcare provider before taking or stopping any medication during pregnancy to discuss the potential risks and benefits.
First Trimester is High-Risk: The first trimester is a crucial period for fetal development and is most vulnerable to teratogens, which can cause severe birth defects.
Avoid Certain Prescription Drugs: Highly teratogenic medications like isotretinoin, warfarin, and certain anticonvulsants (e.g., valproic acid) and antihypertensives (ACE inhibitors/ARBs) must be avoided.
Use Caution with OTCs: NSAIDs like ibuprofen and naproxen should be avoided, especially after 20 weeks, and high-dose Vitamin A is also unsafe. Acetaminophen is generally the safest pain relief option.
Stay Away from Harmful Substances: Alcohol, tobacco, and illegal drugs like cocaine and cannabis are harmful during pregnancy and should be completely avoided.
Never Stop Abruptly: If you are taking a medication for a chronic condition, do not stop it suddenly without consulting your doctor, as this could be more dangerous than continuing.
Herbal Supplements Are Not Always Safe: Many herbal remedies and dietary supplements lack sufficient safety data for pregnant women and should be avoided unless approved by a healthcare professional.

Understanding Teratogens and Pregnancy Risks

During pregnancy, a developing fetus is highly vulnerable to external factors, including medications and other substances. The first trimester, a critical period known as organogenesis when the baby's major organs are forming, is particularly susceptible to harm from teratogens—agents that can cause congenital malformations. In 2015, the U.S. Food and Drug Administration (FDA) replaced the old pregnancy letter categories (A, B, C, D, X) with a new Pregnancy and Lactation Labeling Rule (PLLR) that provides more detailed, evidence-based information for healthcare providers. This change highlights the nuanced risks and benefits associated with different medications.

The Importance of Consulting Your Healthcare Provider

Before taking or stopping any medication, it is essential to consult with a healthcare professional. For some chronic conditions, continuing a prescription medicine may pose less risk to the pregnancy than the untreated illness itself. For example, a woman with a severe condition like epilepsy may need to continue medication, but her doctor can help switch to the safest known treatment option. Never abruptly stop a prescribed medication without medical guidance.

Specific Prescription Drugs to Avoid

Several classes of prescription drugs are known to be unsafe during pregnancy due to their teratogenic effects. These include:

Retinoids: Oral retinoids, such as isotretinoin (formerly Accutane), are highly teratogenic and can cause severe birth defects affecting the brain, heart, and nerves. Women of childbearing age who take this medication must participate in a risk management program like iPLEDGE. Topical retinoids like tretinoin are also generally avoided.
Anticoagulants (Blood Thinners): The blood-thinning drug warfarin (Coumadin) can cause fetal warfarin syndrome, leading to skeletal abnormalities, nasal hypoplasia, and damage to the central nervous system, particularly during weeks 6 through 9 of gestation.
Antihypertensives: Certain blood pressure medications, specifically ACE (angiotensin-converting enzyme) inhibitors like lisinopril and ARBs (angiotensin II receptor blockers) like losartan, can harm the fetus's kidneys and affect amniotic fluid levels.
Anticonvulsants: Some anti-seizure medications, including valproic acid and carbamazepine, are associated with a higher risk of neural tube defects like spina bifida and other structural malformations. Safer alternatives are often available under a doctor's guidance.
Lithium: Used to treat bipolar disorder, lithium can increase the risk of heart defects if taken during the first trimester, when the fetal heart develops.
Tetracycline Antibiotics: This class of antibiotics, including doxycycline, should be avoided as they can cause permanent teeth discoloration and affect bone growth in the baby.
Other Medications: Methotrexate, used for arthritis and certain cancers, can significantly increase the risk of miscarriage and birth defects. Antithyroid drugs like methimazole also pose risks.

Over-the-Counter and Lifestyle Substances to Avoid

Pregnancy safety extends beyond prescriptions to include common OTC medications, supplements, and lifestyle choices. While they may seem harmless, many can negatively impact a developing baby.

Over-the-Counter (OTC) Drugs and Supplements:

Nonsteroidal Anti-Inflammatory Drugs (NSAIDs): Medications like ibuprofen (Advil, Motrin) and naproxen (Aleve) should be avoided, especially after 20 weeks of pregnancy. They can harm the baby's kidneys and heart and affect blood circulation. Acetaminophen (Tylenol) is often considered a safer alternative for pain relief.
High-Dose Vitamin A: Excessive intake of Vitamin A from supplements or certain foods can be teratogenic, causing a range of birth defects.
Herbal Remedies: Many herbal products and supplements are not regulated and lack sufficient safety data for use in pregnancy. Some, like blue cohosh, have been linked to harm. Always consult a healthcare provider before using any herbal product.

Recreational and Lifestyle Substances:

Alcohol: There is no safe amount of alcohol consumption during pregnancy. Alcohol can cause Fetal Alcohol Syndrome (FAS), leading to abnormal facial features, growth problems, and central nervous system issues.
Tobacco: Smoking passes carcinogenic chemicals to the fetus, increasing the risk of heart defects, low birth weight, and Sudden Infant Death Syndrome (SIDS).
Illegal Drugs: Substances like cocaine, methamphetamine, heroin, and cannabis are extremely dangerous during pregnancy and can cause miscarriage, preterm birth, low birth weight, and various birth defects.

Comparison of Common Pain Relief Medications in Pregnancy


Medication Category	Examples	Pregnancy Safety	Reason for Caution/Avoidance
NSAIDs	Ibuprofen (Advil, Motrin), Naproxen (Aleve)	Avoid, especially after 20 weeks	Can affect fetal circulation, kidney function, and amniotic fluid levels.
Acetaminophen	Tylenol, Paracetamol	Generally considered safe (first-line)	Considered the safest option for pain and fever relief throughout pregnancy when used as directed.
Aspirin (High-Dose)	Pain relief products containing aspirin	Avoid	High doses can affect fetal circulation, particularly in later pregnancy. Low-dose aspirin may be prescribed by a doctor for specific conditions like pre-eclampsia.
Codeine	Prescribed pain medication	Use with caution	Can cause neonatal withdrawal symptoms if used frequently or for prolonged periods, especially near delivery.

Conclusion

Navigating medication use during pregnancy requires careful consideration and professional guidance. While many medications are safe, several, particularly retinoids like isotretinoin, the anticoagulant warfarin, and NSAIDs like ibuprofen, are proven to be unsafe and can cause serious harm to a developing baby. The first trimester is a period of heightened risk for birth defects from teratogenic exposures. The most important action any pregnant person can take is to discuss all medications, including prescriptions, OTCs, vitamins, and supplements, with a healthcare provider. Never stop a prescribed medication without medical supervision, and always seek expert advice to ensure the safest treatment plan for both mother and child.

For more detailed information, the Centers for Disease Control and Prevention (CDC) provides extensive resources on medicine and pregnancy.

Frequently Asked Questions

A teratogen is an agent, such as a drug or environmental substance, that can cause or increase the incidence of a congenital malformation in a developing fetus. Exposure is most dangerous during the first trimester, when vital organs are forming.

NSAIDs, such as ibuprofen and naproxen, are generally considered unsafe during pregnancy, particularly after 20 weeks. High-dose aspirin is also not recommended for pain relief.

No, isotretinoin is highly teratogenic and must be avoided during pregnancy. It can cause severe birth defects. All women of childbearing age taking this medication must be enrolled in a special program to prevent pregnancy.

If you took a medication before you knew you were pregnant, you should contact your healthcare provider immediately. Some medications are harmless, but a doctor can assess the potential risks based on the drug and the timing.

No, herbal remedies and dietary supplements should be avoided during pregnancy unless specifically approved by your healthcare provider. Many lack safety data and some have been shown to be harmful.

No, not all antibiotics are unsafe. Certain types like tetracyclines and fluoroquinolones are typically avoided. A doctor will determine if an antibiotic is necessary and prescribe a safe option for your condition.

Alcohol is dangerous because it can cause Fetal Alcohol Syndrome (FAS), which leads to permanent and severe physical, mental, and behavioral disabilities. There is no known safe amount of alcohol during pregnancy.