Diphenhydramine and Pregnancy
In animal studies on pregnancy and diphenhydramine, the medication did not cause any problems when it was given to pregnant rabbits or rats. Since the full risks of using this drug during human pregnancy are not known, however, you should never take diphenhydramine products without your healthcare provider's approval. If you are taking this medicine and pregnancy occurs, notify your healthcare provider immediately.
Safety of Diphenhydramine During Pregnancy
Diphenhydramine (Benadryl®, Sominex®, and many other brand names) is an antihistamine used for various different purposes, such as for treating allergies or insomnia. Based on animal studies, this medication does not appear to present a risk to a developing fetus, although the full effects in humans are not currently known.
Pregnancy Category B
The U.S. Food and Drug Administration (FDA) uses a pregnancy category system to classify the possible risks to a fetus when a specific medicine is taken during pregnancy. Pregnancy Category B is given to medicines that have not been adequately studied in pregnant humans but do not appear to cause harm to the fetus in animal studies. Medications that have been shown to be safe for use in pregnant humans (but have caused problems in laboratory animals) are also given a Category B rating.
In studies, giving very large doses of this drug to pregnant rabbits and rats did not increase the risks of any problems. In human studies (which have not been adequate enough to fully characterize the safety of the medication), diphenhydramine seems to be fairly safe for use during pregnancy. There is some preliminary evidence that it might increase the risk of cleft palate, but these early findings need to be confirmed by further research. Also, the use of antihistamines in general during the last two weeks of pregnancy seems to increase the risk of retinopathy of prematurity (an eye problem in premature infants that can lead to blindness).
Sometimes, diphenhydramine is used "off-label" for the treatment of morning sickness. However, do not use this medication to treat morning sickness without your healthcare provider's approval. Typically, it is used for very severe cases that have not responded to other treatments.