Pregnancy Drug Safety Categories
FDA pregnancy risk categories A, B, C, D, and X explained
Important: Always consult your healthcare provider
Never start or stop a medication during pregnancy without medical advice. The FDA replaced letter categories with a narrative format (PLLR) in 2015, but the letter system is still widely referenced. Your doctor will weigh the specific risks and benefits for your situation.
Risk Scale
Safe
Likely Safe
Caution
Risky
Contraindicated
Category A: Safe
Adequate, well-controlled studies in pregnant women have not shown an increased risk of fetal abnormalities. These medications are considered safe.
Common Examples
Levothyroxine (Synthroid)
Essential for thyroid function; stopping during pregnancy is riskier than continuing.
Folic Acid
Recommended for all pregnant women to prevent neural tube defects.
Category B: Likely Safe
Animal studies have not demonstrated a fetal risk, but there are no adequate studies in pregnant women. Generally considered safe when benefits outweigh risks.
Common Examples
Metformin (Glucophage)
Commonly used for gestational diabetes. Increasing evidence supports safety.
Amoxicillin
One of the safest antibiotics during pregnancy for treating infections.
Acetaminophen (Tylenol)
Preferred pain reliever during pregnancy.
Category C: Caution
Animal studies have shown adverse effects on the fetus, but there are no adequate studies in humans. May be used if the potential benefit justifies the potential risk.
Common Examples
Prednisone
May be necessary for severe asthma or autoimmune conditions. Use the lowest effective dose.
Fluconazole (Diflucan)
Single low dose may be acceptable; high or prolonged doses linked to birth defects.
Tramadol
Use only when no safer alternatives exist and benefits clearly outweigh risks.
Category D: Risky
There is positive evidence of human fetal risk based on adverse reaction data. However, the drug may still be used if the benefit is critical and no safer alternative exists (e.g., life-threatening situations).
Common Examples
Lisinopril (and all ACE inhibitors)
Can cause fetal kidney damage, low amniotic fluid, and skull defects. Switch before pregnancy.
Warfarin (Coumadin)
Causes warfarin embryopathy. Switch to heparin-based anticoagulants during pregnancy.
Phenytoin (Dilantin)
Associated with fetal hydantoin syndrome. Discuss alternatives with your neurologist.
Category X: Contraindicated
Studies in animals or humans have demonstrated fetal abnormalities. The risk clearly outweighs any possible benefit. These drugs must NEVER be used during pregnancy.
Common Examples
Isotretinoin (Accutane)
Causes severe birth defects. Requires two forms of contraception and monthly pregnancy tests (iPLEDGE program).
Methotrexate
Used as an abortifacient — causes miscarriage and severe birth defects. Stop at least 3 months before conception.
Thalidomide
Notorious for causing limb deformities. Strictly controlled distribution.
Planning a Pregnancy?
- Review ALL medications (including OTC and supplements) with your doctor before conceiving.
- Some medications need to be stopped weeks or months before pregnancy (e.g., methotrexate, isotretinoin).
- Don't stop prescribed medications abruptly — some conditions are more dangerous untreated.
- Start folic acid (400-800 mcg daily) at least 1 month before conception.