Omeprazole is used to treat certain stomach and esophagus problems (such as acid reflux, ulcers). It works by decreasing the amount of acid your stomach makes. It relieves symptoms such as heartburn, difficulty swallowing, and persistent cough. This medication helps heal acid damage to the stomach and esophagus, helps prevent ulcers, and may help prevent cancer of the esophagus. Omeprazole belongs to a class of drugs known as proton pump inhibitors (PPIs).
I never read side effects to begin with, finding that one can imagine some when suggested! I found no relief whatsoever from taking omeprazole and quite a lot of the side effects, I don't have the leaflet any more so cannot be more specific I'm afraid. I do remember that they were bad enough and worrying enough for me to cease taking it.