Most common side effects reported in patients taking generic Pepcid tablets included headache, constipation, diarrhea, and dizziness. As the body adjusts to the medication these side effects should fade. If they persist or worsen, consult a local physician. Talk to a local doctor immediately if rare but serious conditions such as easy bruising, irregular heartbeat, persistent fever or sore throat, yellowing of skin, dark urine, or stomach and abdominal pain occur.