Belonging to a group of drugs called histamine-2 blockers, Famotidine works by decreasing the amount of acid the stomach produces, whereas Calcium and magnesium are naturally occurring minerals that neutralize acid in the stomach. As for the combination of famotidine, calcium, and magnesium, it is typically used to relieve heartburn associated with acid indigestion and sour stomach. It is worth noting that this product contains an antacid which may react with other medications, preventing them from being fully absorbed by your body. So, you should talk with your doctor or pharmacist about how to schedule your medications to prevent this problem. As far as the side effects are concerned, they include diarrhea, headache, constipation, or stomach cramps. However, you must notify your doctor immediately if any of these unlikely but serious side effects occur: easy bruising or bleeding, fast, slow, or irregular heartbeat, signs of infection such as fever, persistent sore throat, cough, or seizure. Bear in mind that during pregnancy, the combination of famotidine, calcium, and magnesium should be used only when clearly needed, which is why it is necessary that you discuss the risks and benefits with your doctor. As a matter of fact, this drug passes into breast milk, so you must also consult your doctor before breast-feeding.