Benicar (Olmesartan) is prescribed to treat high blood pressure. It is linked to severe gastrointestinal side effects. These serious side effects can sometimes take months or years to develop. In some instances, the gastrointestinal problems resulting from these drugs have been severe enough to require immediate medical attention or hospitalization. In 2013, the Food and Drug Administration issued a drug safety communication warning the public about these side effects and approved changes in the drugs’ labels to make sure these issues are clearly spelled out. The FDA reports that numerous serious cases have been found and cites research from the Mayo Clinic linking these drugs to severe gastrointestinal problems.