Which over-the-counter medication is known to potentially decrease milk supply?

Pseudoephedrine is known to potentially decrease milk supply due to its effects as a decongestant. It works by constricting blood vessels and reducing blood flow to mucus membranes, which can have a side effect on the mammary glands, leading to a reduction in milk production. This is particularly important for breastfeeding mothers to consider, as maintaining an adequate milk supply is essential for feeding their infants.

In contrast, medications like acetaminophen and ibuprofen are generally considered safe for use during breastfeeding and do not have a significant impact on milk supply. Diphenhydramine, while an antihistamine that can cause drowsiness, is more likely to have sedative effects rather than directly decreasing milk production, although it can sometimes lead to decreased milk let-down in specific cases.