Is My Medication Safe During Pregnancy?

Why does pregnancy change how a medication behaves?

Pregnancy rewrites how your body handles virtually every medication. Blood volume expands by roughly 40 to 50 percent, kidney filtration speeds up, liver enzyme activity shifts, and drug-binding proteins in the blood decline 1Ref 1Coppola P, Kerwash E, Nooney J, Omran A, Cole S (2022).Pharmacokinetic data in pregnancy: A review of available literature data and important considerations in collecting clinical data.Pregnancy causes major pharmacokinetic changes including expanded blood volume, increased renal clearance, and altered enzyme activity that change how medications behave. A dose that was appropriate before pregnancy may become too high or too low. A drug that seems routine outside pregnancy may behave differently in the context of fetal development.

The research gap makes this harder. For ethical reasons, pregnant people have historically been excluded from clinical drug trials, leaving a genuine evidence gap for many medications 2Ref 2Pernia S, DeMaagd G (2016).The New Pregnancy and Lactation Labeling Rule.The FDA Pregnancy and Lactation Labeling Rule (2015) abolished letter categories and requires narrative risk summaries; it notes the old system lumped drugs with evidence of adverse effects together with those having no data (60% were category C), conflating 'no data' with 'known harm' - so insufficient data is not the same as known harm.. The FDA's Pregnancy and Lactation Labeling Rule (PLLR), which replaced the old A-B-C-D-X letter categories beginning in 2015, now requires manufacturers to provide a narrative risk summary and — critically — to weigh the risks of medication use against the risks of the untreated condition 2Ref 2Pernia S, DeMaagd G (2016).The New Pregnancy and Lactation Labeling Rule.The FDA Pregnancy and Lactation Labeling Rule (2015) abolished letter categories and requires narrative risk summaries; it notes the old system lumped drugs with evidence of adverse effects together with those having no data (60% were category C), conflating 'no data' with 'known harm' - so insufficient data is not the same as known harm.. "Insufficient data" is not the same as "known harmful."

The core clinical balance: what is the risk of the medication to fetal development, versus the risk of an untreated or undertreated condition to both you and the baby? These are not equal — and that is exactly what your clinician is trained to weigh.

Which medications are lower-risk, which need a discussion, and which are avoided?

These are general frameworks — not rules for any individual pregnancy. Always confirm with your OB or prescribing clinician.

Often considered lower risk with appropriate use: - Acetaminophen for pain and fever — generally preferred over ibuprofen, especially in the second half of pregnancy. Ibuprofen and other NSAIDs carry risks to the baby's cardiovascular system in the third trimester. - Many antibiotics — amoxicillin, azithromycin, and cephalosporins are commonly used in pregnancy when treatment is needed. Some classes (tetracyclines, fluoroquinolones) are generally avoided. - Prenatal vitamins and folate — essential throughout pregnancy. - Most topical medications — systemic absorption is generally much lower than oral medications.

Requires careful risk-benefit discussion with your clinician: - Antidepressants (SSRIs/SNRIs): ACOG recommends against withholding or discontinuing mental health medications based on pregnancy status alone 3Ref 3American College of Obstetricians and Gynecologists (2023).Treatment and Management of Mental Health Conditions During Pregnancy and Postpartum: ACOG Clinical Practice Guideline No. 5.ACOG Clinical Practice Guideline No. 5 (2023) makes a STRONG RECOMMENDATION against withholding or discontinuing medications for mental health conditions due to pregnancy or lactation status alone, covering antidepressants, anxiolytics, mood stabilizers, and antipsychotics.. Between 10 and 16 percent of pregnant people meet criteria for depression, and discontinuing antidepressant treatment is associated with a high relapse risk 4Ref 4Lebin LG, Novick AM (2022).Selective Serotonin Reuptake Inhibitors (SSRIs) in Pregnancy: An Updated Review on Risks to Mother, Fetus, and Child.SSRI use in pregnancy carries low absolute risk of adverse outcomes; risks of untreated maternal depression include relapse rates estimated at 68% with discontinuation; individualized risk-benefit discussion is recommended. A 2022 review found that low absolute risks of adverse outcomes with SSRIs must be weighed against the well-documented harms of untreated maternal depression 4Ref 4Lebin LG, Novick AM (2022).Selective Serotonin Reuptake Inhibitors (SSRIs) in Pregnancy: An Updated Review on Risks to Mother, Fetus, and Child.SSRI use in pregnancy carries low absolute risk of adverse outcomes; risks of untreated maternal depression include relapse rates estimated at 68% with discontinuation; individualized risk-benefit discussion is recommended. Sertraline has the most reassuring pregnancy track record among SSRIs; paroxetine is generally avoided. This is a nuanced conversation — not a simple yes or no. - Blood pressure medications: Some are widely accepted as safe in pregnancy (labetalol, nifedipine, methyldopa); others (ACE inhibitors, ARBs) are contraindicated because of documented fetal kidney harm and are avoided in all trimesters. Blood pressure that is too high in pregnancy independently poses serious risks, including preeclampsia and eclampsia. - Seizure medications (anti-seizure medications / ASMs): Stopping a seizure medication during pregnancy can cause breakthrough seizures, which carry risks of miscarriage, preterm labor, and direct injury. Physiologic changes in pregnancy alter drug clearance — particularly for lamotrigine and levetiracetam — meaning levels may need monitoring and dose adjustment, not stoppage 5Ref 5Various (PMC review) (2022).Management of Anti-Seizure Medications during Pregnancy: Advancements in The Past Decade.Review of anti-seizure medications in pregnancy: lamotrigine plasma concentrations fall 40-60% (UGT1A4 induction by estradiol) and levetiracetam clearance rises (increased renal blood flow/GFR), so levels require monitoring and dose adjustment; subtherapeutic ASM concentrations increase seizure frequency, raising the risk of miscarriage and preterm labor.. Lamotrigine, oxcarbazepine, and levetiracetam have more reassuring fetal safety profiles than older agents; this requires a neurologist and OB working together. - Thyroid medications: Untreated hypothyroidism is associated with miscarriage, gestational hypertension, and adverse neurodevelopment in the baby. Thyroid replacement is generally continued, with TSH monitored and doses adjusted upward as needed through pregnancy. - Asthma inhalers: Uncontrolled asthma in pregnancy is associated with preterm birth, low birth weight, and increased perinatal mortality — risks that, for most patients, outweigh the risks of continuing a controller inhaler 6Ref 6Wang H, Li N, Huang H (2020).Asthma in Pregnancy: Pathophysiology, Diagnosis, Whole-Course Management, and Medication Safety.Uncontrolled asthma in pregnancy is associated with preterm birth, low birth weight, and increased perinatal mortality; inadequate treatment poses greater risk than continuing inhaler therapy; budesonide is the best-studied inhaled corticosteroid in pregnancy. Budesonide is the best-studied inhaled corticosteroid in pregnancy. NAEPP guidelines and a 2020 clinical review both conclude that inadequate asthma treatment poses greater risk than medication use 6Ref 6Wang H, Li N, Huang H (2020).Asthma in Pregnancy: Pathophysiology, Diagnosis, Whole-Course Management, and Medication Safety.Uncontrolled asthma in pregnancy is associated with preterm birth, low birth weight, and increased perinatal mortality; inadequate treatment poses greater risk than continuing inhaler therapy; budesonide is the best-studied inhaled corticosteroid in pregnancy.

Generally avoided in pregnancy: - Ibuprofen and most NSAIDs (especially third trimester) - Tetracyclines, fluoroquinolones, sulfonamides near term - Isotretinoin (Accutane) — a known major teratogen. The FDA requires the iPLEDGE program and negative pregnancy tests before each prescription precisely because exposure in pregnancy causes severe, life-threatening birth defects. Not to be used under any circumstances during pregnancy 7Ref 7Vallerand IA, Lewinson RT, Farris MS, Sibley CD, Ramien ML, Bulloch AGM, Patten SB (2018).Efficacy and adverse events of oral isotretinoin for acne: a systematic review.Isotretinoin is a known major teratogen; FDA requires iPLEDGE program with mandatory pregnancy testing before each prescription; pregnancy during treatment causes severe, life-threatening birth defects. - ACE inhibitors and ARBs (all trimesters; associated with fetal renal failure) - Warfarin (contraindicated in certain windows of pregnancy) - Some psychiatric medications depending on class and trimester

What are the two mistakes that each cause harm?

Stopping a prescription medication abruptly because it sounds scary. This is one of the most common — and most well-meaning — ways people put themselves and their pregnancies at risk. Uncontrolled hypertension, a breakthrough seizure, a depressive relapse, or an untreated infection can each harm the pregnancy, sometimes severely. ACOG explicitly recommends against discontinuing psychiatric medications based on pregnancy status alone 3Ref 3American College of Obstetricians and Gynecologists (2023).Treatment and Management of Mental Health Conditions During Pregnancy and Postpartum: ACOG Clinical Practice Guideline No. 5.ACOG Clinical Practice Guideline No. 5 (2023) makes a STRONG RECOMMENDATION against withholding or discontinuing medications for mental health conditions due to pregnancy or lactation status alone, covering antidepressants, anxiolytics, mood stabilizers, and antipsychotics.. Never stop a prescription without talking to your OB or prescribing clinician first.

Continuing a medication that is genuinely contraindicated because "the doctor prescribed it." Some medications are started before a pregnancy is known. Your prescribers need to know you are pregnant — this information does not always cross specialty lines automatically. Double-checking is appropriate and reflects good self-advocacy. Stopping without guidance is not.

The right step in either direction is contact: a patient portal message, a phone call, or a telehealth visit. Many medication questions can be addressed without an in-person appointment. If your situation involves multiple medications or a complex condition, your OB may refer you to a maternal-fetal medicine (MFM) specialist — this is routine good care, not a signal that something is wrong.

Does the trimester change the risk?

Drug risk in pregnancy is not uniform across the nine months. Three windows matter differently:

First trimester (weeks 1–12): This is the period of organogenesis — when the baby's major organ systems form. It is generally the highest-risk window for drug-related structural birth defects. Fetal thyroid hormone production does not begin until around 18 weeks; until then, the fetus depends entirely on maternal thyroid hormone transfer, which is why hypothyroidism treatment should not be interrupted in early pregnancy.

Second trimester (weeks 13–26): Often the lower-risk window for many medications. Organ formation is largely complete. This trimester is also when an anatomy ultrasound can be used to evaluate fetal development if there was a concerning exposure earlier.

Third trimester (weeks 27–40): Carries its own set of concerns. NSAIDs in the third trimester can cause premature closure of the ductus arteriosus (a fetal heart vessel). Some medications — especially those affecting the central nervous system — can affect the newborn's adaptation after birth and may require neonatal monitoring.

A drug that carries higher risk in the first trimester may be considered acceptable in the second. One that is routine in early pregnancy may be avoided near delivery. Trimester is a key variable in every medication conversation during pregnancy.

What should I ask my OB or prescriber?

A prepared conversation tends to be more productive and complete. These questions help structure it:

• What does the available evidence say about this specific medication — is it "known risky," "probably safe," or "data limited"?
• Does the risk differ by trimester?
• What are the risks of leaving my condition untreated during pregnancy?
• Is there a pregnancy-preferred alternative that is as effective for my condition?
• If I need to switch or taper a medication, how do we do that safely?
• Are there any special precautions for my newborn related to this medication?

For complex situations — multiple medications, a serious chronic condition, or a drug with known higher fetal risk — ask for a referral to a maternal-fetal medicine (MFM) specialist. The MotherToBaby service (mothertobaby.org), run by the Organization of Teratology Information Specialists, also provides free, evidence-based information on specific exposures during pregnancy and breastfeeding. If you take more than one medication, bring the full list — how they interact with each other is part of the same conversation.