What Does Olmesartan 20 mg Do? Understanding its Therapeutic Action

October 8, 2025 •

4 min read

According to the Centers for Disease Control and Prevention, nearly half of all adults in the U.S. have high blood pressure, and for many, an effective treatment involves medication like olmesartan 20 mg. This drug, part of a class known as angiotensin II receptor blockers (ARBs), works by relaxing blood vessels to effectively and safely lower high blood pressure.

Quick Summary

Olmesartan 20 mg is a medication that primarily treats high blood pressure by blocking a hormone that constricts blood vessels. This action causes blood vessels to relax, reducing pressure and helping to prevent future strokes, heart attacks, and kidney damage.

Key Points

Mechanism of Action: Olmesartan 20 mg is an angiotensin II receptor blocker (ARB) that prevents the hormone angiotensin II from constricting blood vessels.
Primary Use: It is primarily prescribed for treating hypertension (high blood pressure) in adults and children over 6 years old.
Long-Term Benefits: By lowering blood pressure, the medication reduces the risk of serious long-term complications like heart attacks, strokes, and kidney problems.
Typical Use: The standard starting strength for adults is typically 20 mg once daily, but may be adjusted by a doctor based on blood pressure response.
Common Side Effects: Some patients may experience mild side effects such as dizziness, headache, or flu-like symptoms.
Serious Risks: Rare but serious side effects can include angioedema (swelling), hyperkalemia (high potassium levels), and a severe, chronic diarrhea called sprue-like enteropathy.
Contraindications: The medication is contraindicated during pregnancy due to the risk of fetal harm.

Mechanism of Action: How Olmesartan Works

Olmesartan 20 mg belongs to a class of medications called angiotensin II receptor blockers (ARBs). Its mechanism is centered on the body's renin-angiotensin-aldosterone system (RAAS), a hormonal pathway that regulates blood pressure. The steps of this mechanism include:

Angiotensin II Blockade: The active metabolite of olmesartan, olmesartan medoxomil, blocks the binding of angiotensin II to specific receptors known as AT1 receptors. Angiotensin II is a potent vasoconstrictor, meaning it narrows blood vessels.
Vessel Relaxation: By blocking the AT1 receptors, olmesartan prevents the tightening of blood vessels, allowing them to relax and widen. This process, called vasodilation, reduces overall blood pressure.
Aldosterone Inhibition: The blockade also inhibits the release of aldosterone, a hormone that causes the body to retain sodium and water. This leads to a reduction in fluid retention, which further contributes to lower blood pressure.

This cascade of effects makes olmesartan an effective treatment for hypertension by reducing the workload on the heart and arteries. The 20 mg strength is often used in adult patients.

Therapeutic Effects of Olmesartan 20 mg

In treating high blood pressure, the 20 mg strength of olmesartan delivers significant therapeutic benefits that go beyond just lowering blood pressure readings.

Reduced Risk of Cardiovascular Events

By controlling hypertension, olmesartan helps prevent severe long-term complications. Untreated high blood pressure can cause significant damage to blood vessels in the brain, heart, and kidneys, leading to serious events. Regular use of olmesartan helps reduce the risk of:

Heart Attacks: The reduction in workload on the heart helps prevent myocardial infarction.
Strokes: Relaxed blood vessels decrease the risk of a stroke.
Heart Failure: By easing the strain on the heart, it lowers the risk of heart failure over time.

Efficacy and Monitoring

Clinical trials have demonstrated the effectiveness of olmesartan, with a noticeable reduction in blood pressure typically occurring within two weeks of starting treatment. Maximum effect is usually observed around four weeks. Doctors closely monitor a patient's progress and may adjust the medication based on individual needs.

Potential Side Effects and Precautions

Like any medication, olmesartan 20 mg can cause side effects. Most are mild, but some serious reactions are possible. A patient's care team will monitor for these effects during treatment.

Common Side Effects

Dizziness or lightheadedness, especially when standing up quickly
Headache
Flu-like symptoms
Back pain

Serious Adverse Effects

Hyperkalemia: Elevated potassium levels can occur, particularly in patients with kidney problems or those taking other potassium-raising medications.
Angioedema: A rare but serious allergic reaction causing swelling of the face, lips, tongue, or throat. Immediate medical attention is required.
Sprue-like Enteropathy: In very rare cases, long-term use can lead to severe, chronic diarrhea with weight loss and intestinal damage. This is typically reversible upon stopping the medication.
Kidney Injury: In susceptible individuals, such as those with severe heart failure or renal artery stenosis, changes in kidney function can occur.

Important Precautions

Pregnancy: Olmesartan is contraindicated during pregnancy, particularly in the second and third trimesters, as it can cause fetal harm or death.
Kidney Function: Renal function should be monitored regularly, especially in patients with existing kidney impairment.
Dehydration: Excessive sweating, vomiting, or diarrhea can cause a significant drop in blood pressure. Patients should stay hydrated.
Potassium Supplements: Patients should avoid potassium supplements or salt substitutes unless directed by their doctor, due to the risk of hyperkalemia.

Comparison of Olmesartan with Other ARBs

Olmesartan is one of several angiotensin II receptor blockers available. While all ARBs share a similar mechanism, there are subtle differences in efficacy, particularly in the initial weeks of treatment.


Feature	Olmesartan	Losartan	Valsartan	Irbesartan
Effectiveness	Greater reduction in blood pressure than losartan or valsartan in the first 8 weeks.	Effective, but studies show less initial reduction compared to olmesartan.	Effective, but less initial reduction in blood pressure than olmesartan in some studies.	Similar efficacy to olmesartan at recommended uses.
Onset of Action	Significant blood pressure reduction often seen within 2 weeks.	Effective after initial use, similar to olmesartan over a longer term.	Effective after initial use.	Similar rapid onset of action as olmesartan.
Side Effects	Similar to other ARBs; higher risk of rare sprue-like enteropathy.	Generally well-tolerated, similar side effect profile to other ARBs.	Generally well-tolerated, similar side effect profile to other ARBs.	Generally well-tolerated, similar side effect profile to other ARBs.
Pregnancy	Contraindicated.	Contraindicated.	Contraindicated.	Contraindicated.

Conclusion

In summary, olmesartan 20 mg is a safe and effective angiotensin II receptor blocker used primarily for the treatment of hypertension. It works by blocking the effects of angiotensin II, leading to blood vessel relaxation and a reduction in blood pressure. This helps lower the risk of serious cardiovascular events such as heart attack and stroke over the long term. While the 20 mg strength is a standard starting point for many patients, it is important to take the medication exactly as prescribed and be aware of potential side effects, including the very rare risk of sprue-like enteropathy. Regular monitoring by a healthcare provider is essential to ensure efficacy and patient safety. For more detailed clinical information, patients should consult authoritative medical resources and their doctor. For example, the FDA's prescribing information provides comprehensive details on the drug's approved uses and warnings.

This information is not a substitute for professional medical advice. Always consult your doctor or pharmacist regarding your medical condition and treatment.

Frequently Asked Questions

Olmesartan begins to reduce blood pressure within about two weeks of starting treatment. The full therapeutic effect is typically achieved after four weeks of consistent use.

If you miss a dose, take it as soon as you remember on the same day. If you do not remember until the next day, skip the missed dose and resume your regular schedule. Do not take a double dose to compensate.

No. Olmesartan is contraindicated during pregnancy, as it can cause serious harm or even death to an unborn baby, particularly during the second and third trimesters.

Yes. You should avoid using potassium supplements or salt substitutes containing potassium, as olmesartan can increase potassium levels in the blood. Discuss any dietary concerns or changes with your doctor.

The most common side effects of olmesartan include dizziness, headache, and fatigue. These are often mild and may improve over time as your body adjusts.

Clinical studies suggest that olmesartan can be more effective at lowering blood pressure than losartan and valsartan, particularly in the first few weeks of treatment. However, the best medication depends on individual factors and should be determined by a healthcare provider.

Sprue-like enteropathy is a rare but serious side effect of olmesartan that can cause severe, chronic diarrhea and significant weight loss. It is often reversible upon stopping the medication.