Diphenhydramine (Benadryl) is generally considered safe for occasional use during pregnancy. The CDC and MotherToBaby report no consistent link to birth defects, and ACOG recognizes older antihistamines like this one as acceptable options for allergies and sleep in pregnancy. As with any medication, use the lowest effective dose for the shortest time, and check with your provider before regular use.
Benadryl's active ingredient is diphenhydramine, a first-generation antihistamine used for allergies, itching, and sometimes as a sleep aid. The FDA groups it among the older sedating antihistamines. Note that some products sold under the Benadryl name in different countries contain different active ingredients, so always check the label. This page addresses diphenhydramine specifically.
ACOG and the NHS generally list diphenhydramine among the antihistamines considered acceptable during pregnancy, and large studies have not shown a clear increase in birth defects. However, it is sedating and can cause drowsiness, and evidence is stronger for occasional than for regular high-dose use. Because it crosses the placenta, clinicians typically favour the lowest effective dose for the shortest time. It is not recommended as a routine or long-term sleep aid.
Avoid combining it with alcohol or other sedating medicines, and be cautious near your due date, as heavy use close to delivery has been linked in some reports to effects on the newborn. If allergies are the issue, ACOG notes that non-sedating antihistamines like loratadine or cetirizine are also commonly used and may be preferred for ongoing symptoms. For nausea or sleep, ask your provider about options tailored to pregnancy rather than self-treating repeatedly.