I was on Prilosec previously and had a lot of bad side effects- Dizziness, stomach upset, headaches, and so on. GI doc suggested I try nexium instead, and this has worked marvelously for me. I occasionally get a mild headache, but usually that's in tandem with another headache trigger (allergies, for example). I took it once a day for a 28 day course to heal my esophagus from a long gerd attack, and now I'm tapering down to every other day and will eventually aim for once or twice a week as the permanent maintenance dose