I was found to have a serious reaction to Omeprazole in 2005 - in particular hypomagnesemia, hypocalcemia and hypokalemia, after a 3 month period of reduced health including gout, tetany, muscle cramps etc etc. Hospital specialists were unaware of a connection with Omeprazole which was eventually discovered by myself and my general practitioner experimenting with stopping drug use and checking blood tests for Mg+ especially.