Hi I am Dr.kadhir, Olmesartan is a safe drug, rare side effects include cough, abdominal pain, headache, flu like infections. They can be taken for prolonged use, but is is important to check electrolytes, renal and hepatic status once in every 6 months. It is important to discuss the drug interactions with your doctor before you take other medicines. It is contraindicated if there is allergy to the drug, during pregnancy, breast feeding, if suffering from liver, heart or kidney diseases. Thank you for the consultation in health care magic.