This is what I found on a site call drug.com: Omeprazole Side Effects
Brand Names: Prilosec, Prilosec OTC
Please note - some side effects for Omeprazole may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.
Side Effects of Omeprazole - for the Consumer
All medicines may cause side effects, but many people have no, or minor, side effects. Check with your doctor if any of these most COMMON side effects persist or become bothersome when using Omeprazole/Sodium Bicarbonate:
Diarrhea; gas; headache; nausea; stomach pain; vomiting.
Seek medical attention right away if any of these SEVERE side effects occur when using Omeprazole/Sodium Bicarbonate:
Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue; unusual hoarseness); bone pain; chest pain; dark urine; fast, slow, or irregular heartbeat; fever, chills, or sore throat; red, swollen, blistered, or peeling skin; seizures; severe diarrhea; severe stomach pain or cramps; swelling of the hands, ankles, or feet; unusual bruising or bleeding; unusual or sudden weight increase; unusual tiredness; vision changes; yellowing of the eyes or skin.
This is not a complete list of all side effects that may occur. If you have questions about side effects, contact your health care provider. Call your doctor for medical advice about side effects. To report side effects to the appropriate agency, please read the Guide to Reporting Problems to FDA.