The main adverse effects of taking omeprazole are: First, some patients taking omeprazole may have dry mouth or mild abdominal distension, diarrhea, nausea, vomiting and other symptoms, and a few patients may have mild elevation of glutamate transaminase and glutathione transaminase, but the symptoms can generally be improved after stopping the drug. Second, dizziness, headache, drowsiness, insomnia and other neuropsychiatric symptoms may occur. Third, there may be some endocrine system changes, such as vitamin B12 deficiency. Fourth, there will be allergic reactions, such as rash, hives, etc.