Pregnancy Drug Categories: What Do They Mean?

In 1975, the FDA introduced categories to determine if a medication would be safe for pregnancy. Over the years, it has become clear that drug safety in pregnancy isn’t always quite that easy. A new system of defining drug safety in pregnancy is due out in the future but has yet to be introduced. In the meanwhile, we are left with the system introduced in 1975, and still currently in place, to decide medication safety for pregnancy. It is important that women who are pregnant, or considering pregnancy, understand the drug categories and what they mean.

What are the categories?

The categories are lettered A, B, C, D, and X.  Their definitions are as follows:

  • A – Controlled studies in pregnant women demonstrated no risk to the fetus during any part of the pregnancy, examples are folic acid and vitamin B6.
  • B – No adequate controlled studies in pregnant women exist and animal studies show no fetal risk, examples are Tylenol and insulin.
  • C – No adequate controlled studies in pregnant women exist and animal studies show adverse fetal risk that may be outweighed by the benefit of the drug, examples are Ciprofloxacin and Diflucan.
  • D – Studies in humans, investigational or post marketing data, have demonstrated fetal risk that may be outweighed by the benefit of the drug, examples are Dilantin and most chemotherapy drugs.
  • X – Studies in humans or animals, investigational or post marketing data, demonstrate fetal abnormalities or risk that outweighs any possible drug benefit, examples are accutane and thalidomide.

So how does this translate into practice?

Anyone looking at this would think, “well, just take category A drugs of course.” The truth is category A drugs are very few. Controlled studies in pregnant women just don’t happen because of the fetal risk if something goes wrong. The majority of “safe drugs” are actually category B drugs and as a provider category B always gets the green light.

Category C and D drugs are a little trickier. They are used--but only in situations where the benefit of the drug will outweigh the risk to the fetus. That is an important decision that is made by your provider prescribing the medication. Finally, pregnant women or those planning pregnancy should never take category X drugs.  So if you are pregnant or planning to be pregnant, review your medications with your provider and make sure they are safe for you and your baby.

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