Answer
Yes, diphenhydramine in Benylin Mucus Cough Night crosses the placenta, although levels have not been reported, and the product should not be used during pregnancy unless the potential benefit to the mother outweighs possible risks to the developing foetus.
Sources for this answer
- Benylin Mucus Cough NightMcNeil Products Ltd · emc · SmPC §4.6 Fertility, pregnancy and lactation · Version 9Document updated
Sources checked