Do you notice how IG influencers often startposts with “I always get asked about…”. Let me start this blog with that same phrase. Haha

I always get asked about medications in pregnancy. Which ones are safe? The FDA uses a class or category system for drugs in pregnancy:

Category A

Adequate and well-controlled studies have failed to demonstrate a risk to the fetus in the first trimester of pregnancy (and there is no evidence of risk in later trimesters).

Example drugs or substances: levothyroxine, folic acid

Category B

Animal reproduction studies have failed to demonstrate a risk to the fetus and there are no adequate and well-controlled studies in pregnant women.

Example drugs: metformin, amoxicillin

Category C

Animal reproduction studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks.

Example drugs: gabapentin, trazodone

Category D

There is positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experience or studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks.

Example drugs: losartan

Category X

Studies in animals or humans have demonstrated fetal abnormalities and/or there is positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experience, and the risks involved in use of the drug in pregnant women clearly outweigh potential benefits.

Example drugs: methotrexate, finasteride

We follow this guidance. Until 2019 we also leaned on the MotherRisk program out of Sick Kids Hospital in Toronto for advice and to stay up to date on the latest information on drugs in pregnancy. Now, we look for data from several different sources.

In any case, I am often asked about the safety of medications in pregnancy. The category of prescription medications are often known, but what about over the counter medications?

I am often surprised at what items people are taking based on non-medical advice and it worries me. I am a worry wart (probably a good quality in a doctor, but it also means I bite my nails and lie awake worrying about patients many nights). I am also quite conservative in all my advice (e.g. I tell pregnant women not to have sex or exercise aggressively until successful past 8-10 weeks of pregnancy based on no good evidence).

Anyway, a very well done review of common over the counter medication (Tylenol/paracetamol, NSAIDs and aspirin) used in pregnancy drives home that being a worry wart about medications in pregnancy is a good idea.

Reference: Zafeiri A, Mitchell RT, Hay DC, Fowler PA. Over-the-counter analgesics during pregnancy: a comprehensive review of global prevalence and offspring safety. Hum Reprod Update. 2021 Jan 4;27(1):67-95.

What does this review of studies on over the counter analgesics tell us?

• Aspirin is clearly safe.
• NSAIDs (e.g. Advil) are clearly not safe
• Tylenol is more controversial with some studies suggesting an increased risk of ADHD and ASD, while other studies not suggesting such an association.

The authors suggest (as they often do) that more research on duration and timing of exposure is needed.  I think this review is comprehensive enough and includes a large enough number of pregnant women that, from it, we can advise pregnant women to avoid over the counter analgesics like NSAIDs and Tylenol if possible. Of course, everyone must weigh the risks of using these medications and the benefits.

Dr. Beth Taylor MD, FRCSC

Reproductive Endocrinology & Infertility