It’s important to note that taking Theraflu while breastfeeding is generally safe, but it might have some effect on your milk supply.
Theraflu is a common over-the-counter cold and flu remedy with ingredients like acetaminophen, phenylephrine, and sometimes diphenhydramine. While these ingredients are usually considered safe for breastfeeding, they can potentially impact milk production.
Similarly, diphenhydramine1 , an antihistamine found in some Theraflu products, is generally safe but could possibly impact milk supply with regular or high-dose use. It's also worth mentioning that diphenhydramine can cause drowsiness in both nursing people and babies.
Because of these potential effects on milk supply, it's a wise move to consult with your healthcare provider before taking Theraflu or any medication while breastfeeding.