Olmesartan

Key facts

• Olmesartan (sold as Benicar) is an angiotensin II receptor blocker (ARB) that relaxes blood vessels to lower blood pressure. It is also used to protect the kidneys in some people with diabetes and high blood pressure.
• It is taken once daily, with or without food, and the full blood-pressure-lowering effect can take a few weeks to appear.
• Olmesartan must not be used during pregnancy. It can injure and even be fatal to the developing baby, particularly in the second and third trimesters.
• Seek urgent care for facial or throat swelling, or for severe, unexplained diarrhoea and weight loss that develops months or years into treatment.

What olmesartan treats

Olmesartan treats high blood pressure (hypertension), on its own or combined with other blood-pressure medicines. Lowering blood pressure with an ARB reduces long-term risk of stroke, heart attack, and kidney damage. It is not a rescue treatment for a sudden hypertensive crisis and does not relieve chest pain.

How olmesartan works

Olmesartan blocks the receptor that the hormone angiotensin II uses to tighten blood vessels. With that signal blocked, vessels stay relaxed and the heart pumps against less resistance, which lowers blood pressure over time.

Before you take it

• Do not take olmesartan if you are pregnant or could become pregnant without reliable contraception; switch to a pregnancy-safe blood pressure medicine as soon as pregnancy is confirmed or planned.
• Tell your prescriber about kidney disease, liver disease, or if you are on dialysis, since dosing may need adjustment.
• Combining olmesartan with potassium supplements, potassium-sparing diuretics, or high-dose ACE inhibitors can raise potassium to dangerous levels.
• NSAIDs such as ibuprofen can reduce olmesartan's effect and increase the risk of kidney injury, especially if you are dehydrated or elderly.

Side effects

Common effects include dizziness, headache, tiredness, and mild diarrhoea or stomach upset.

Stop and seek urgent medical care for any of these:

• Swelling of the face, lips, tongue, or throat, or sudden difficulty breathing.
• Chronic, severe, watery diarrhoea with substantial weight loss, which can develop long after starting treatment.
• Signs of high potassium: muscle weakness, tingling, or an irregular heartbeat.
• Little or no urine output, or swelling in the legs and ankles.

Safety essentials

• Olmesartan is contraindicated in pregnancy; drugs that act on the renin-angiotensin system can cause fetal injury and death, so contraception is essential for anyone who could become pregnant.
• Olmesartan is linked to a rare but severe sprue-like enteropathy, causing chronic diarrhoea and major weight loss that can appear months to years after starting; this needs prompt medical evaluation and usually resolves once the drug is stopped.
• Kidney function and blood potassium are checked periodically, especially after starting treatment or increasing the dose.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.