Get emergency medical help if you have signs of an allergic reaction to omeprazole: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.
Stop using this medicine and call your doctor at once if you have:
severe stomach pain, diarrhea that is watery or bloody;
new or unusual pain in your wrist, thigh, hip, or back;
seizure (convulsions);
kidney problems - fever, rash, nausea, loss of appetite, joint pain, urinating less than usual, blood in your urine, weight gain;
low magnesium - dizziness, irregular heartbeats, feeling jittery, muscle cramps, muscle spasms, cough or choking feeling; or
new or worsening symptoms of lupus - joint pain, and a skin rash on your cheeks or arms that worsens in sunlight.
Taking omeprazole long-term may cause you to develop stomach growths called fundic gland polyps. Talk with your doctor about this risk.
If you use omeprazole for longer than 3 years, you could develop a vitamin B-12 deficiency. Talk to your doctor about how to manage this condition if you develop it.
Common omeprazole side effects may include:
cold symptoms such as stuffy nose, sneezing, sore throat (especially in children);
fever (especially in children);
stomach pain, gas;
nausea, vomiting, 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.
 Omeprazole side effects (more detail)
