Note: This document contains side effect information about hydrochlorothiazide / olmesartan. Some of the dosage forms listed on this page may not apply to the brand name Benicar HCT. Learn about the potential side effects of Benicar (olmesartan). Includes common and rare side effects information for consumers and healthcare professionals. Includes common and rare side effects information for consumers and healthcare professionals. Most side effects are mild to moderate and may go away with time, but others may be more severe or last for a long period of time. In some cases, Benicar side effects can become serious or may be life-threatening. Luckily for most patients taking Benicar or other olmesartan products, the more common side effects are less severe than olmesartan. Most commonly people experience a little dizziness or a feeling of being lightheaded. These symptoms usually diminish and completely disappear with time. Find information about common, infrequent and rare side effects of Benicar Oral. Of the reported Benicar side effects, the most common one is dizziness, which occurs in up to 3 percent of people taking the medication. Serious side effects that should be reported immediately to your healthcare provider include unexplained skin rash, difficulty breathing or swallowing, and hair loss. Benicar HCT (olmesartan medoxomil-hydrochlorothiazide) is a combination of an angiotensin II receptor antagonist and a thiazide diuretic (water pill) used to treat high blood pressure (hypertension). Common side effects of Benicar HCT include dizziness or lightheadedness as your body adjusts to the medication. Benicar (olmesartan medoxomil) is an angiotensin II receptor antagonist used to reduce and control hypertension (high blood pressure). Generic Benicar is available outside of the U.S. Common side effects of Benicar include: Common Side Effects of Benicar Like most medications, the ARB class including Benicar has a number of side effects. Most of the side effects are not life threatening or permanently disabling and may decrease in severity after the patient has been taking Benicar for a period of time. Find information about common, infrequent and rare side effects of Benicar HCT Oral.