Are Any Medications Truly Safe in Pregnancy? What Science Knows (and Still Doesn’t)
What Drugs Are Safe During Pregnancy? Why We Still Don’t Fully Know
If you’ve ever stood in front of a medicine cabinet with a positive pregnancy test in one hand and a headache, infection, or flare-up in the other, you’re not alone. Pregnant people are often told to “avoid all medications if possible,” yet many need treatment for chronic conditions, mental health, or acute illnesses such as COVID‑19. The uncomfortable truth is that, for decades, we simply haven’t had good data on which drugs are truly safe during pregnancy — but that is finally starting to change.
This page explains why pregnant people were historically excluded from drug trials, what new research (including COVID‑19 vaccine data and policy changes) is revealing, and how you and your clinician can make the safest possible decisions with the evidence we have today.
“Pregnancy should not be a reason to automatically exclude people from potentially beneficial research. It should be a reason to do research carefully and ethically.”
— Perinatal research ethicists, summarized from current consensus statements
The Core Problem: A Shocking Lack of Drug Safety Data in Pregnancy
Most modern medicines have never been rigorously studied in pregnant people. For years, clinical trials automatically excluded anyone who was pregnant or might become pregnant, largely out of a desire to “protect the fetus.” The result is a paradox: pregnant people still need treatment, but clinicians must rely on limited observational data, animal studies, or post‑market registries instead of robust trial evidence.
Research published in leading journals and summarized in Nature reports that for many commonly used medications — from pain relievers to immune therapies — we still can’t say with high confidence whether they are fully safe, risky, or somewhere in between during pregnancy. That uncertainty can lead to:
- Undertreatment of serious conditions (for example, stopping asthma or depression medication “just in case”).
- Over‑cautious avoidance of drugs that are likely safe and beneficial.
- Use of older drugs simply because we know a bit more about them, not because they are necessarily better.
How We Got Here: Why Pregnant People Were Excluded from Drug Trials
The current caution around drugs in pregnancy is rooted in painful history. Two major events reshaped research ethics:
- Thalidomide (late 1950s–1960s): A sedative used for morning sickness caused severe birth defects in thousands of babies worldwide. This tragedy highlighted how medicines can cross the placenta and harm developing fetuses.
- Diethylstilbestrol (DES): A synthetic estrogen given to prevent miscarriage was later linked to rare cancers and fertility problems in the children exposed in utero.
In response, regulators demanded stricter safety standards. Unfortunately, the pendulum swung so far toward protection that pregnant people were classified as a “vulnerable population” and largely barred from trials altogether. Instead of designing better, safer research, the system avoided research on pregnancy almost entirely.
Today, many experts argue that this approach has created avoidable risks: we are effectively testing medicines in pregnant people anyway, but in an uncontrolled, post‑market way — without the safeguards of a formal clinical trial.
COVID‑19 Vaccines: A Turning Point in Pregnancy Drug Research
The COVID‑19 pandemic forced the medical community to confront its knowledge gap. At first, pregnant people were not included in the pivotal trials of mRNA vaccines. Yet they faced higher risks from severe COVID‑19, including ICU admission, preterm birth, and other complications.
As vaccines rolled out, many pregnant people and their clinicians had to make decisions in real time, with minimal data. Observational studies and real‑world surveillance systems (such as pregnancy registries and large health‑system databases) quickly became crucial sources of information.
Multiple large studies and surveillance efforts now show that:
- mRNA COVID‑19 vaccines reduce the risk of severe COVID‑19 in pregnant people.
- No increase has been seen in major birth defects, miscarriage rates, or preterm birth linked to vaccination.
- Vaccination during pregnancy can provide antibodies that help protect the newborn in early life.
Major obstetric and infectious‑disease societies now recommend COVID‑19 vaccination during pregnancy, based on accumulating safety and effectiveness data from millions of pregnancies.
This experience has energized calls to routinely include pregnant people in research — with careful ethics, built‑in safety monitoring, and informed consent — instead of excluding them by default.
What We Do Know: Commonly Used Drugs and Pregnancy Safety
Even with the data gaps, we have decades of clinical experience and an expanding body of research for many common medicines. Below is a high‑level overview — not a substitute for personalized care, but a starting point for conversations with your provider.
Generally Considered Low‑Risk When Used as Directed
- Acetaminophen (paracetamol): Often preferred for pain and fever in pregnancy when used at recommended doses and for the shortest time needed. Some observational studies have raised questions about long‑term child neurodevelopment, but findings are inconsistent and may be confounded by the underlying illness. Most guidelines still support cautious, short‑term use.
- Many antibiotics: Penicillins and certain cephalosporins are widely used to treat infections in pregnancy. Untreated infections can be more dangerous than the drugs used to treat them.
- Antihistamines: Medications such as loratadine and cetirizine are typically considered low‑risk for allergy relief in later trimesters, based on observational data.
- Some antidepressants (e.g., SSRIs): For moderate to severe depression, SSRIs like sertraline are often used, balancing small, potential neonatal risks against the well‑documented harms of untreated maternal depression.
Medications That Require Extra Caution or Alternatives
- Non‑steroidal anti‑inflammatory drugs (NSAIDs): Ibuprofen and related drugs may be used with caution in early pregnancy but are generally avoided in the third trimester because they can affect the fetal heart and kidneys and lower amniotic fluid.
- Some anti‑seizure medicines: Uncontrolled seizures are dangerous for both parent and fetus, but certain drugs (like valproate) are strongly linked to birth defects and developmental disorders. Neurology and maternal‑fetal medicine teams often switch to safer regimens before or early in pregnancy.
- Blood pressure medications: Some classes, such as ACE inhibitors and ARBs, are typically avoided in later pregnancy because of known fetal risks. Others (like labetalol or nifedipine) are preferred.
Clearly Known to Be Harmful in Pregnancy
- Isotretinoin (for severe acne): Strongly teratogenic — associated with a high risk of serious birth defects. Strict pregnancy prevention programs are in place in many countries.
- Certain chemotherapy agents and immune‑modulating drugs: Some are incompatible with pregnancy, while others can be used only in specific circumstances or trimesters; decisions require specialist input.
- Warfarin (a blood thinner): Typically avoided during pregnancy because of risk of fetal bleeding and birth defects; alternatives such as heparin are usually preferred.
Why Studying Drugs in Pregnancy Is So Challenging
It’s understandable to wonder: if we can run large cancer or heart‑disease trials, why is pregnancy so difficult to study? Researchers point to several factors:
- Two patients in one: Any intervention may affect both the pregnant person and the developing fetus, and those effects can vary across trimesters.
- Changing physiology: Pregnancy alters blood volume, kidney function, liver metabolism, and more. A “standard dose” in non‑pregnant adults may have very different effects during pregnancy.
- Ethical complexities: Informed consent must address potential fetal risks and uncertain long‑term outcomes. Regulators and ethics boards have historically erred on the side of exclusion to avoid even theoretical harm.
- Long‑term follow‑up: Some effects might not become apparent until years later (for example, fertility or neurodevelopment), requiring extended monitoring of children exposed in utero.
Despite these challenges, experts increasingly argue that carefully designed research is more ethical than leaving pregnant people to navigate medication use in an evidence vacuum.
A Real‑World Story: Balancing Vaccine Decisions in Pregnancy
Consider the experience, described in Nature, of a pregnant person who became pregnant in 2021, just as COVID‑19 vaccines were rolling out. Her healthcare team acknowledged that pregnant people had not been part of the earliest vaccine trials, so there were no randomized data specific to pregnancy. At the same time, emerging observational data showed higher risks of severe COVID‑19 in pregnant people compared with non‑pregnant peers.
Together, they considered:
- Her personal risk factors (work exposure, underlying health conditions).
- Risks of severe COVID‑19 to her and the fetus.
- Early safety surveillance data from pregnant people who had already chosen vaccination.
She ultimately chose to be vaccinated during pregnancy. Ongoing research and registries have since strengthened the evidence that this decision, for many, reduces overall risk. Her story illustrates how, even with limited initial data, shared decision‑making and evolving evidence can guide safer choices.
How to Make Safer Decisions About Medications During Pregnancy
There is rarely a perfect, risk‑free option. The goal is to make decisions that minimize overall risk — not just theoretical drug risks, but also the real dangers of untreated illness.
1. Clarify the Health Problem You’re Treating
- Is it a minor, short‑term issue (like a mild headache or seasonal allergy)?
- Or a serious or chronic condition (asthma, epilepsy, diabetes, depression, autoimmune disease)?
The more serious the condition, the more likely that treatment is safer than no treatment.
2. Review All Medications and Supplements
- List prescription drugs, over‑the‑counter medicines, herbal products, and vitamins.
- Bring photos of labels or a written list to your appointment.
- Do not assume “natural” means safe in pregnancy; some herbs can stimulate the uterus or affect hormones.
3. Ask Key Questions at Your Appointment
- What are the known risks of this medication in pregnancy?
- What are the risks of not treating my condition?
- Is there a safer alternative we can try?
- Is the dose appropriate for pregnancy, or does it need adjustment?
- Are there registries or ongoing studies I could participate in to help improve knowledge?
4. Use the Lowest Effective Dose for the Shortest Time
For many short‑term medications, clinicians aim to:
- Use the smallest dose that effectively controls symptoms.
- Limit how long you take the drug when possible.
- Reassess at each prenatal visit whether the medicine is still needed.
5. Do Not Stop Chronic Medications Abruptly Without Advice
Abruptly stopping medication for conditions like epilepsy, high blood pressure, or depression can be dangerous. Always talk with your prescriber first; many regimens can be adjusted rather than stopped.
Common Obstacles — and How to Overcome Them
Obstacle 1: Conflicting Advice
It’s common to hear one clinician say a medication is “fine” and another say to avoid it. Guidelines evolve as new studies are published.
What can help:
- Ask how recent the information is and whether it’s based on specific guidelines.
- Request that your clinicians coordinate (for example, your obstetrician and your neurologist speaking directly).
- Consider a maternal‑fetal medicine consultation for complex decisions.
Obstacle 2: Fear of Blame
Many pregnant people express intense guilt or fear that any medicine might “cause harm,” especially after reading alarming stories online.
What can help:
- Focus on absolute risk (how likely something is) rather than just hearing that a risk “exists.”
- Ask your clinician to explain risks in numbers or comparisons you can understand.
- Remember that taking care of your own health is one of the best ways to protect your baby.
Obstacle 3: Misinformation Online
Online forums and social media can offer support but may also spread inaccurate or outdated claims about drugs and pregnancy.
What can help:
- Use reputable health sites connected to major hospitals, universities, or government agencies.
- Be wary of sources promoting miracle cures or selling products as “100% safe in pregnancy.”
- Bring confusing information to your clinician to discuss together.
The Future: How Research Is Finally Catching Up
In response to COVID‑19 and ongoing advocacy, agencies and researchers are rethinking how to include pregnant people in drug development. Current initiatives described in Nature and other scientific outlets include:
- Pregnancy‑specific clinical trials: More studies now enroll pregnant participants from the start, especially for vaccines and treatments for conditions like HIV, malaria, and autoimmune diseases.
- Better use of registries and real‑world data: Large health systems and national databases are tracking pregnancy exposures and outcomes to quickly detect potential safety signals.
- Updated regulatory guidance: Some regulators now encourage planning for pregnancy data earlier in drug development rather than treating it as an afterthought.
- Patient and public involvement: Pregnant people and advocacy groups are increasingly involved in trial design, helping ensure that studies are acceptable, understandable, and responsive to real‑world needs.
Increasingly, experts argue that “protection through research” — not protection from research — is the ethical path forward for pregnant people.
Before and After Better Data: How Decisions Can Change
To visualize the impact of research progress, consider a simplified comparison of how decisions might look before and after robust pregnancy data are available for a medication:
| Stage | Before Good Pregnancy Data | After Robust Pregnancy Studies |
|---|---|---|
| Risk assessment | Heavy reliance on animal data and case reports; wide uncertainty. | Clearer estimates of risk by trimester and dose; better counseling. |
| Clinical decisions | Often default to older alternatives or stopping treatment. | Ability to balance benefits and risks using concrete numbers. |
| Patient experience | High anxiety, conflicting opinions, lingering doubt. | More confidence, clearer guidance, shared decisions grounded in evidence. |
Key Takeaways: What You Can Do Right Now
While the scientific community works to close the knowledge gap, there are concrete steps you can take to navigate medication use during pregnancy more safely.
- Don’t go it alone: Involve your obstetric provider, relevant specialists, and, when needed, maternal‑fetal medicine experts.
- Bring a complete list of medications and supplements to your appointments, including over‑the‑counter products.
- Ask for evidence‑based resources your clinician trusts, and be cautious about anecdotal stories online.
- Weigh the risks of untreated illness as carefully as the potential risks of medication.
- Consider participating in registries or studies if offered — this can help improve care for future parents and babies.
Moving Forward: From Uncertainty to Informed Choice
The question “What drugs are safe during pregnancy?” still doesn’t have as many clear, confident answers as it should. That’s not because pregnant people are an afterthought, but because the research system historically tried to protect them by keeping them out of studies. Now, driven by lessons from COVID‑19 and growing advocacy, that mindset is shifting.
Even in this imperfect landscape, you are not powerless. By working closely with knowledgeable clinicians, asking focused questions, and relying on high‑quality evidence where it exists, you can make thoughtful, informed choices that protect both your health and your baby’s.
If you’re currently pregnant or planning a pregnancy and have questions about a specific medication, consider scheduling a dedicated visit with your healthcare provider to review every drug and supplement you take. Bringing your concerns into the open is the first — and most important — step toward safer, more confident decisions.
