Take this medication by mouth as directed by your doctor, usually once daily with or without food. If this medication causes you to urinate more frequently, it is best to take it at least 4 hours. 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. Common Side Effects of Benicar. Tell your doctor if the following side effect becomes severe or doesn't go away: Dizziness; Joint, muscle, or back pain Along with its needed effects, olmesartan (the active ingredient contained in Benicar) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention. Other Benicar Side Effects 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. Drug Information on Benicar HCT (hydrochlorothiazide and olmesartan) includes drug pictures, side effects, drug interactions, directions for use, symptoms of overdose, and what to avoid. Find information about common, infrequent and rare side effects of Benicar HCT Oral. 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.