Demystifying Drug Categories for Pregnant Women

by Jodi Razgaitis

When women first learn they are pregnant most will embark on a program of good nutrition, exercise and general wellness to avoid causing harm to themselves and their growing baby. Although some women may forgo treatments without any health consequences, mothers who require medication for a chronic health condition will be faced with a dilemma: continue therapy and possibly risk harm to their baby or risk under-treating a serious illness, which can be harmful to both. But how do you know what drugs are safe during pregnancy?

How Drugs are Deemed Safe for Humans

The Food and Drug Administration (FDA), the government agency that oversees the safety of drugs, evaluates all the available research studies that test the safety and efficacy of new drugs. Experimental drugs are first tested on animals to determine an initial level of safety. If they are deemed sufficiently safe, the drugs are then tested on humans. These studies are often "well controlled", meaning that the study includes a group of patients receiving the experimental drug and another group receiving either an approved drug, or an inactive substance (placebo).

Most drugs however, are not tested in pregnant women to avoid the potential harm to the mother and fetus. Additionally, if a drug is considered safe to take early in the first trimester, it may turn out to be harmful during the last few months of pregnancy as the body's physiology changes throughout pregnancy. Still, there are some drugs that initially had an unclear safety rating but later received a safe rating after many women taking the drug during pregnancy had no ill effects.

So the FDA has created a system that assigns a safety category -- A, B, C, D and X -- which must be applied to the labels of all drugs. While this may look like a bad game of Scrabble, these letters represent very important information about drug safety during pregnancy. Since 1996, every drug label includes a statement about the drug's known effects on pregnancy.

This system, which has been criticized for its vague definitions and use of medical jargon, can be difficult to interpret. But an understanding of how these categories are assigned can help pregnant women make very important decisions.

FDA Pregnancy Category Chart

This chart resembles a tier, with the safest drugs falling under the category A, the least-safe drugs at the bottom in the category X.

Category Description
A Adequate, well-controlled studies in pregnant women have not shown an increased risk of fetal abnormalities.
B Animal studies have revealed no evidence of harm to the fetus, however there are no adequate and well-controlled studies in pregnant women or animal studies have shown an adverse effect, but adequate and well-controlled studies in pregnant women have failed to demonstrate a risk to the fetus.
C Animal studies have shown an adverse effect and there are no adequate and well-controlled studies in pregnant women. or No animal studies have been conducted and there are no adequate and well-controlled studies in pregnant women.
D Studies, adequate well-controlled or observational, in pregnant women have demonstrated a risk to the fetus. However, the benefits of therapy may outweigh the potential risk.
X Studies, adequate well-controlled or observational, in animals or pregnant women have demonstrated positive evidence of fetal abnormalities. The use of the product is contraindicated in women who are or may become pregnant.

Category A
Drugs that fall under category A have had several well-controlled studies that found no harmful effects or increase in birth defects. These drugs have all had studies conducted in pregnant woman with positive results. Very few drugs fall into this category. Prenatal vitamins receive a category A rating.

Category B
Drugs assigned a category B rating are not likely to pose a threat to the fetus from the evidence in animal studies, but no well-controlled studies have been performed in pregnant women. However, a drug may also receive a category B rating if animal studies have shown evidence of fetus damage but the same drug tested on pregnant women posed no threat.

Category C
A category C rating is given to drugs that have been shown to be harmful in animal studies but no studies have been conducted on pregnant humans. Drugs may also receive a category C rating if the drug was not studied in animals and there isn't enough evidence from studies in pregnant humans. This implies that the drug may or may not be safe to take.

Category D
Drugs receive a category D rating when the drugs have been tested in well-controlled or observational (not controlled) studies, which resulted in harm to the unborn baby. In some cases these drugs may still be given if the benefits to the mother outweigh the risks to the baby (for example, cancer treatment).

Category X
A Category X rating is assigned to drugs that should never be used during pregnancy, as there are no benefits that would exceed the potential risk.

Continued Surveillance

The FDA is continually monitoring the safety of drugs during pregnancy. The drug manufacturers are required to collect feedback from pregnant women who are taking their drug, and to report these findings to the FDA.

Ultimately, all drug treatment decisions during pregnancy should be made under the guidance of a physician. To ensure the best outcome for you and your baby, discuss all over-the-counter drugs, prescription medications, dietary supplements and herbal preparations with your doctor.

Copyright © Jodi Razgaitis. Permission to republish granted to, LLC.


Submitted by kmstep523 on

The FDA is in the process of revising this system and getting rid of the alphabet soup in favor of more detailed info. There are several problems with this system. For example, the system makes it sound like a B is better than a D, when we actually have some human data for a D drug and the benefits of taking may outweigh the risk; the categories are rarely changed despite new evidence; a drug that may be a "D" in the first trimester is not necessarily contraindicated in later pregnancy and vice versa; an X drug may be so because it doesn't need to be used in pregnancy, such as statins. See for more info.