Olmesartan is a medicine used to treat high blood pressure (hypertension) . It belongs to a class of drugs called angiotensin receptor blockers (ARBs) and works by relaxing blood vessels so that blood can flow more easily. Lowering high blood pressure helps prevent strokes, heart attacks, and kidney problems. Olmesartan is usually taken once daily with or without food, and the dosage is based on the patients medical condition and response to treatment. It usually takes about a week for olmesartan to start reducing high blood pressure, and it may take 2 to 8 weeks to take full effect. The main side effects of olmesartan are feeling dizzy, headaches, and flu-like symptoms, but they are usually mild and only last for a short time. If you are being sick (vomiting) or have severe diarrhea because of a stomach bug or illness while taking olmesartan, tell your doctor. You may need to stop taking it until you feel better. It is important not to use salt substitutes such as Lo-Salt because they are high in potassium. When mixed with olmesartan, they may make the level of potassium in your blood too high.