Instructed patient on medication Irbesartan, it is used to treat high blood pressure (hypertension). Lowering high blood pressure helps prevent strokes, heart attacks, and kidney problems. It works by relaxing blood vessels so that blood can flow more easily. Dizziness, lightheadedness, or upset stomach may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly. To reduce the risk of dizziness and lightheadedness, get up slowly when rising from a sitting or lying position.