Get emergency medical help if you have any of these signs of an allergic reaction to omeprazole: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.
Call your doctor at once if you have:
diarrhea that is watery or bloody; or
low magnesium (dizziness, confusion, fast or uneven heart rate, jerking muscle movements, jittery feeling, muscle cramps, muscle weakness or limp feeling, cough or choking feeling, seizure).
Common omeprazole side effects may include:
fever;
cold symptoms such as stuffy nose, sneezing, sore throat;
stomach pain, gas;
nausea, vomiting, mild diarrhea; or
headache.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.