Once you are prescribed and buy Prevacid, then most medications can cause side effects which can be defined as an unwanted response to a medication when it is taken in normal doses. Side effects can range from mild or severe, temporary or permanent. Side effects are not experienced all patients who take this medication. Many side effects can be managed, and others may go away over time. Stop using Prevacid and contact your doctor if you experience any of the following symptoms: Dizziness, confusion, Fast or uneven heart rate, Jerking muscle movements, Feeling jittery, Muscle cramps, muscle weakness or limp feeling, Cough or choking feeling, Seizure (convulsions) Less serious side effects may include: Headache, Nausea, stomach pain, Diarrhea, Constipation Immediately seek medical help if you experience signs of an allergic reaction including hives; difficulty breathing and swelling of your face, lips, tongue, or throat. This is not a complete list of side effects and others may occur. Call your doctor for medical advice about additional side effects that you may experience.