Olmesartan, sold under the trade name Benicar among others, is a medication used to treat high blood pressure, heart failure, and diabetic kidney disease. It is a reasonable initial treatment for high blood pressure. It is taken by mouth. Versions are available as the combination olmesartan/hydrochlorothiazide and olmesartan/amlodipine. Common side effects include dizziness, headaches, diarrhea, and back pain. Serious side effects may include kidney problems, low blood pressure, and angioedema. Use in pregnancy may harm the fetus and use when breastfeeding is not recommended. It is an angiotensin II receptor antagonist and works by blocking the effects of angiotensin II. It was patented in 1991 and came into medical use in 2002. It is available as a generic medication. In 2020, it was the 139th most commonly prescribed medication in the United States, with more than 4million prescriptions. Medical uses Olmesartan is used for the treatment of hypertension. It may be used alone or in combination with other antihypertensive agents. The U.S. Food and Drug Administration (FDA) has determined that the benefits of olmesartan continue to outweigh its potential risks when used for the treatment of patients with high blood pressure according to the drug label. Contraindications Contraindications for treatment with olmesartan include biliary obstruction. Another major contraindication is pregnancy; reports in the scientific literature reveal fetal malformations for pregnant women taking sartan-derived drugs. Adverse effects The incidence of adverse effects with Benicar (the US trade name for olmesartan medoxomil) is reported as similar to placebo; the only adverse effect that occurred in >1% of patients treated with it and more frequently than placebo was dizziness (3% vs 1%). Rarely, olmesartan can cause severe gastrointestinal issues. The symptoms, which include nausea, vomiting, diarrhea, weight loss, and electrolyte abnormalities, are common among those who have celiac disease. Recent studies suggested this form of sprue-like enteropathy could be caused by the inhibition of TGF-β, a polypeptide cytokine that maintains intestinal homeostasis. However, it is still unclear why this action was never observed with other ARBs. In studies of angiotensin II receptor antagonists such as olmesartan, patients with unilateral or bilateral renal artery stenosis, increases in serum creatinine or blood urea nitrogen have been reported. There has been no long-term use of olmesartan medoxomil in patients with unilateral or bilateral renal artery stenosis, but similar results may be expected. The full prescribing information for Benicar notes as with all drugs that act directly