Diphenhydramine (Benadryl) During Pregnancy
Diphenhydramine can be used during pregnancy but should be approached with caution, particularly in the first trimester, due to a potential association with cleft palate that has not been definitively refuted, though recent studies have not detected increased risk for congenital malformations. 1
Key Safety Considerations
The 2008 Joint Task Force on Practice Parameters guideline explicitly states that while diphenhydramine is frequently used during pregnancy and has "good overall safety data," there remains concern over a case-control study suggesting an association with cleft palate development 1. This concern "has yet to be sufficiently refuted" according to the guideline 1.
Risk-Benefit Framework
- First trimester is most critical for potential congenital malformations as organogenesis occurs during this period 1
- Both first-generation and second-generation antihistamines generally have excellent safety records with no significant increase in congenital malformations when used during first trimester 1
- However, diphenhydramine specifically carries the unresolved cleft palate concern that distinguishes it from other antihistamines 1
Preferred Alternatives
Second-generation antihistamines are now considered equally safe with better tolerability profiles. The guideline notes that "the accumulated safety data during pregnancy on the second-generation antihistamines are comparable to those of the first-generation antihistamines" 1. More recent research from 2016 specifically recommends cetirizine and loratadine as the second-generation antihistamines of choice during pregnancy 2.
Why Alternatives Are Preferable
- Diphenhydramine's sedative qualities and impaired performance characteristics make it less desirable than second-generation antihistamines 1
- The FDA drug label warns against use "if pregnant or breast-feeding" 3
- Second-generation agents avoid the anticholinergic and sedating effects while maintaining efficacy
If Diphenhydramine Must Be Used
Dosing
Standard adult dosing is 12.5-25 mg every 4-6 hours as needed 3. The medication has been used successfully in pregnancy for hyperemesis gravidarum at 50 mg every 6 hours intravenously 4, demonstrating that therapeutic doses can be administered when clinically necessary.
Clinical Context Where Use May Be Justified
- Hyperemesis gravidarum requiring hospitalization (proven effective in combination with metoclopramide) 4
- Severe allergic reactions when second-generation antihistamines are unavailable
- Situations where the maternal benefit clearly outweighs the theoretical fetal risk
Common Pitfalls to Avoid
Do not combine with oral decongestants, especially in first trimester, as this increases risk of congenital malformations including gastroschisis and small intestinal atresia 1
Avoid combining with acetaminophen or salicylates when decongestants are also used, as this further increases malformation risk 1
Do not use to induce sleep in pregnancy - the FDA label explicitly warns against using diphenhydramine "to make a child sleepy" 3, and this principle extends to inappropriate use in pregnancy
Avoid in patients with glaucoma, chronic bronchitis/emphysema, or urinary retention per FDA contraindications 3
Clinical Algorithm
For allergic rhinitis/urticaria in pregnancy:
- First choice: Cetirizine or loratadine (second-generation antihistamines) 2
- Second choice: Chlorpheniramine (first-generation with better safety profile than diphenhydramine)
- Consider diphenhydramine only if: alternatives unavailable AND maternal symptoms significantly impact quality of life AND patient counseled about unresolved cleft palate concern
For hyperemesis gravidarum:
- Diphenhydramine 50 mg IV every 6 hours in combination with metoclopramide is an established effective protocol 4
For anaphylaxis:
- Use diphenhydramine as part of standard anaphylaxis management regardless of pregnancy status, as maternal mortality risk outweighs theoretical fetal risk