Pregnancy and FDA Drug Classifications

Pharmaceutical drugs with a pregnancy test

It's important to be careful what goes in your body during pregnancy and FDA drug classifications can help. These classifications can help you understand what medicines have been tested in pregnancy, whether they've been tested on humans or animals, and what the results showed.

Definitions of Pregnancy Drug Classifications

Doctors need to be aware of which drugs are dangerous in pregnancy and FDA drug classifications serve as a guide.

  • Category A. Careful tests in humans have shown no harm.
  • Category B. Animal studies showed some harm, but well-designed studies in humans showed no harm, OR animal studies did not show any harm and there are no good studies in humans.
  • Category C. Animal studies show some harm and there are no good studies in humans, OR no human or animal studies have been done.
  • Category D. Human studies show some risk.
  • Category X. There is strong evidence that the drug causes birth defects, either in humans or in animals.

How the FDA Drug Classifications are Used

Always check with your doctor before taking a drug during pregnancy. Some medicines are safe during one stage of pregnancy but not another.

Category A

Many people think that drugs in FDA Category A are always perfectly safe during pregnancy. That's not strictly true since it's possible that an unforeseen problem will appear. However, doctors feel pretty confident that, if these drugs are needed, the risk of harm is very small.

Category B

Category B drugs are often prescribed in pregnancy. These are drugs that researchers are fairly sure are safe, although they may have shown some risk of birth defects in animals. Category B drugs may have been tested for safety in pregnant women, but not necessarily.

Category C

Category C drugs should be avoided in pregnancy unless there is a clear need. If your doctor prescribes a Category C drug when you're pregnant, ask about alternatives from Category A or B. If no other drug is available, though, and it's something you need, talk to your doctor about what the studies have shown. It may be that the risk is small and that the benefit you'll receive from the drug is significant.

Category D

Category D drugs should be avoided in pregnancy when possible. Since these are drugs that have been tested in humans and have been found to increase the chance of birth defects, they are used during pregnancy only if the benefits clearly outweigh the risks.

Category X

FDA Category X drugs should never be used in pregnancy. These are drugs that clearly cause birth defects, either in humans or in animals.

The Difference Between Animal and Human Studies

The trouble with relying on animal data is that animal and human bodies don't work exactly the same way. A drug that has serious effects in animals may not affect humans at all, and vice versa. In some cases, researchers are able to tell which reactions are unique to the animal being tested. Other times, it's impossible to know if the same thing would happen in humans.

If you're concerned about taking a drug that shows a risk of harm in animals, you may want to find out what kinds of studies were done. Were the animals given high doses, or doses equivalent to what a human would take? Doctors tend to feel more confident about safety when drugs cause problems only at "overdose" levels, meaning that the amount given to animals is much higher than the typical dose for humans. However, many women feel most confident using medicines that have been tested in humans, not just animals, and that showed no increased risk of birth defects.

Risk vs. Certainty

To decide whether to take a drug during pregnancy, you'll need to understand the concept of medical risk. Many people think that if they take a risky medication during pregnancy, they will definitely cause harm to the baby. Medical science is rarely this clear. Most of the time, the reality is that taking a medication could affect the fetus; the decision rests on how likely this is to happen.

One way to think about it is to consider how likely a medicine is to be safe during pregnancy. Category A drugs are very likely to be safe. Category B drugs are probably safe, but they're not as well-tested as Category A. We don't know a lot about the safety of Category C drugs, but they haven't been proven to be unsafe. Category D drugs aren't safe, but they're not guaranteed to be harmful in every case. Category X drugs are very likely to be dangerous in pregnancy.

To Learn More About Pregnancy and FDA Drug Classifications

For answers to common questions about pregnancy and FDA drug classifications, visit the Pregnancy and Medications page at the National Women's Health Information Center.

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