Yes to both questions. Proton pump inhibitors (PPIs) such as omeprazole or pantoprazole have many side effects. Serious reactions include low magnesium levels, clostridium difficicile colitis, blood dyscrasias, and liver impairment. Common reactions include headache, abdominal pain, nausea, diarrhea, vomiting, flatulence, and Vitamin B12 deficiency (from long-term use), and fundic gland polyps (from long-term use). Brand names for PPIs include Prilosec, Nexium and Prevacid, Protonix, and Dexilant.