Benadryl doesn’t interact with Milk of Magnesia and these medications are safe to take together. Taking Milk of Magnesia with Benadryl won’t result in increased side effects compared to taking either medication by itself.
Milk of Magnesia is an antacid and laxative product available over-the-counter as a drinkable liquid or as chewable tablets that is used to treat heartburn, indigestion, and occasional constipation. The dose for treating heartburn and indigestion is lower than the dose for treating constipation, so the package directions should be read carefully (usually the dose for constipation is double the dose for heartburn and indigestion).
The active ingredient in Milk of Magnesia is magnesium hydroxide and it works to relieve heartburn and indigestion by reducing the amount of acid in the stomach. At higher doses, it also draws water into the gut to soften the stool, stimulate to gut to move, and relieves constipation.
Because Milk Of Magnesia contains magnesium, people who have been told to avoid taking magnesium or those who know they have high magnesium levels should not use Milk of Magnesia. Magnesium can interact with some medications by binding to them and keeping them from being absorbed into the body or it can reduce the acid in the stomach that is needed for some drugs to be absorbed.
Benadryl is an antihistamine used to treat allergy symptoms and also as a sleep aid due to its sedative effects. There are no reported interactions with Milk of Magnesia.