Many common medications, including some you can buy without a prescription, are unsafe during pregnancy. The list is long enough that the safest approach is to check every drug, supplement, and herbal product with your provider before taking it. But certain categories carry well-documented risks worth knowing about, from over-the-counter pain relievers to acne treatments to blood pressure drugs.
Pain Relievers: NSAIDs and Aspirin
Ibuprofen (Advil, Motrin), naproxen (Aleve), and aspirin are all nonsteroidal anti-inflammatory drugs, or NSAIDs. These are contraindicated after 28 weeks of pregnancy because they can cause premature closure of a blood vessel in the baby’s heart called the ductus arteriosus. This vessel needs to stay open until birth, and NSAIDs interfere with the chemical signals that keep it dilated.
Even earlier in pregnancy, from about week 20 onward, prolonged NSAID use can reduce the volume of amniotic fluid surrounding the baby by impairing fetal kidney function. This effect is usually reversible once the drug is stopped, but it can restrict fetal growth if it goes undetected. The bottom line: avoid NSAIDs entirely in the second half of pregnancy, and use them only briefly and with medical guidance before that. Acetaminophen (Tylenol) is generally considered the safer alternative for pain relief during pregnancy, though it should still be used at the lowest effective dose.
Decongestants
Pseudoephedrine, the active ingredient in Sudafed and many cold medications, has been linked to an increased risk of a birth defect called gastroschisis, where the baby’s intestines develop outside the abdominal wall. One study found a roughly threefold increase in risk with first-trimester use. While this finding has been called preliminary, pseudoephedrine is a vasoconstrictor, meaning it narrows blood vessels, and that mechanism fits with how this type of defect develops. Saline nasal sprays and steam inhalation are safer alternatives for congestion during pregnancy.
Isotretinoin (Accutane)
Isotretinoin, prescribed for severe acne, is one of the most dangerous drugs a pregnant person can take. Exposure during pregnancy causes major malformations in roughly 15% of live births, affecting the brain, face, heart, ears, and spinal cord. The risk is so severe that the drug is dispensed through a restricted program requiring two negative pregnancy tests before each prescription refill, along with the use of two forms of contraception throughout treatment. If you’re planning a pregnancy, isotretinoin must be stopped at least one month before conception.
Blood Pressure Medications: ACE Inhibitors
ACE inhibitors, a widely prescribed class of blood pressure drugs, can cause serious harm to a developing baby during the second and third trimesters. They damage fetal kidneys and reduce blood flow to the uterus, leading to a cascade of problems: reduced amniotic fluid, restricted growth, underdeveloped skull bones, lung problems, and limb deformities. If you take an ACE inhibitor and become pregnant, your provider will typically switch you to a pregnancy-safe alternative as early as possible.
Certain Seizure Medications
Valproate, used to treat epilepsy and bipolar disorder, carries one of the highest risks of any prescription drug in pregnancy. Children exposed to valproate in the womb have an absolute risk of about 4.4% for autism spectrum disorder, roughly three times the rate seen without exposure. Valproate also increases the risk of physical birth defects, particularly neural tube defects like spina bifida. For people with epilepsy, stopping medication abruptly is dangerous, so the standard approach is to work with a neurologist before conception to find a safer alternative.
Certain Antibiotics
Tetracycline antibiotics (including doxycycline and minocycline) should be avoided after the fourth month of pregnancy. They bind to calcium in developing bones and teeth, causing permanent gray or yellowish-brown discoloration of the baby’s teeth. They may also temporarily slow bone growth, though this appears to reverse after the drug is stopped. Many other antibiotics are safe during pregnancy, so your provider can almost always find a substitute.
Oral Antifungal Medication
Fluconazole (Diflucan), commonly prescribed for yeast infections, poses a risk even at low doses when taken orally during pregnancy. Research shows that doses under 150 mg are associated with more than double the risk of miscarriage, and higher doses increase that risk further. Topical antifungal creams applied directly to the affected area are considered much safer for treating yeast infections during pregnancy.
Herbal Supplements
“Natural” does not mean safe in pregnancy. Several herbal products are actively dangerous:
- Blue cohosh has been used as a folk labor-induction remedy, but it contains a compound that acts like nicotine and another that constricts blood vessels. Case reports describe newborn heart failure and stroke after maternal use.
- Pennyroyal, sometimes marketed as a tea, contains a compound called pulegone that causes severe liver damage. It has been used historically as an herbal abortifacient with sometimes fatal results for the mother.
- Rue is toxic to both the liver and kidneys and can cause multi-organ failure.
These herbs are not regulated for safety or dosing, which makes them even more unpredictable. Avoid all herbal supplements during pregnancy unless specifically cleared by your provider.
Live Vaccines
Live vaccines contain weakened but active viruses, and they should not be given during pregnancy. The CDC lists these as contraindicated:
- MMR (measles, mumps, rubella)
- Varicella (chickenpox)
- Nasal spray flu vaccine (the injected version is safe)
- Certain travel vaccines: yellow fever, typhoid, and Japanese encephalitis
If you’re planning a pregnancy, get the MMR and varicella vaccines at least one month before conceiving. Inactivated vaccines like the flu shot and the Tdap vaccine are not only safe during pregnancy but actively recommended.
How Drug Labels Work Now
You might still see references to the old FDA pregnancy letter categories (A, B, C, D, X), but those have been replaced. Current drug labels include a detailed pregnancy section with a risk summary, clinical considerations, and available data on human and animal studies. They also include information about whether a drug passes into breast milk and whether pregnancy testing or contraception is needed while taking the medication. This system gives more useful, nuanced information than a single letter grade ever could, but it also means you can’t just glance at a category and know the answer. Reading the full label, or asking your pharmacist to walk you through it, is the most reliable way to check.