Ans - Headache is the most frequent side effect of omeprazole. However, it may also result in adverse effects related to the stomach, like nausea, vomiting, or diarrhea. The risk of more severe side effects increases when taking omeprazole in higher dosages or for a longer period of time than a year.   Bone fractures and pneumonia (a lung infection) are two examples of these. Before making it your only form of remedy for your stomach, go to the doctor to treat the root of your issue.