Demystifying Drug Categories for Pregnant Women

08/26/2002

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.