Chlorpheniramine is an antihistamine that is frequently taken to treat allergies and the common cold. It is typically considered safe for use during pregnancy, because it is not known to cause birth defects in humans. It is in Pregnancy Category B, according to the U.S. Food and Drug Administration (FDA), which means no humans have been harmed in studies involving this medication. It can, however, lead to eye problems in premature babies when taken during the last two weeks of pregnancy. For this reason, chlorpheniramine in pregnancy is not usually recommended in the third trimester unless there are no alternatives.
Pregnancy Category B is the second safest group in the FDA's sorting system. It often means a drug has been tested on humans and no harmful effects on the fetus were discovered, though animal studies may have shown some medical issues. It also could mean that, while a drug has not yet been properly tested on humans, animal studies have shown no harmful effects. When it comes to chlorpheniramine, its status as a Category B drug means related studies yielded no birth defects in humans, which is why it is frequently suggested as a safe drug to take, even during the often precarious first trimester, which is when birth defects are often formed.
At the same time, some studies show that taking chlorpheniramine in pregnancy is not advisable in women at-risk for having a premature baby. This is because taking this medication during the last two weeks can increase the odds of a premature baby being born with retinopathy of prematurity. This is an eye problem sometimes found in premature babies; it may lead to blindness when not treated immediately, because the retina can detach. The problem can usually be avoided if women tell their doctors that they have taken chlorpheniramine in pregnancy, because early treatment can prevent long-term damage.
In general, chlorpheniramine is one of the most commonly recommended medications to take when treating allergies and the common cold during pregnancy. The drug's listing as a Pregnancy Category B drug, as opposed to the safer Category A, means pregnant women should take this medication only when necessary. For example, if their runny nose, watery eyes or other symptoms prevent them from sleeping or being able to relax, most women are advised to take chlorpheniramine in pregnancy, because anxiety and lack of sleep tend to be more harmful to the pregnancy than this drug is.