Losartan, also available as the brand-name drug Cozaar, is a prescription medication used to treat high blood pressure and diabetic nephropathy and prevent stroke in adults with high blood pressure and left ventricular hypertrophy.
In 2022, over 53 million losartan prescriptions were written in the United States. Its widespread use highlights the importance of understanding its safety profile and potential side effects, which enables healthcare providers and patients to make informed medical decisions.
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How Losartan Works
Losartan belongs to a class of medications called angiotensin II receptor blockers (ARBs). ARBs can be easily recognized by their names that end in "-sartan." Other examples include:
- Azilsartan (Edarbi)
- Candesartan (Atacand)
- Irbesartan (Avapro)
- Olmesartan (Benicar)
- Telmisartan (Micardis)
- Valsartan (Diovan)
The renin-angiotensin-aldosterone system (RAAS) is one of the main mechanisms by which the body regulates blood pressure, fluid balance, and electrolyte levels. It activates when blood pressure drops or the kidneys sense low blood flow:
- The kidneys release a hormone called renin into the bloodstream.
- Renin converts angiotensinogen (a protein from the liver) into angiotensin I.
- An enzyme called angiotensin-converting enzyme (ACE) converts angiotensin I into angiotensin II.
- Angiotensin II is a hormone that raises blood pressure by constricting blood vessels and triggering aldosterone release from the adrenal glands.
Overactivation of the RAAS contributes to the development and progression of hypertension, heart failure, and diabetic nephropathy. Blocking this system can help treat these diseases. (9)
ARBs target this system by blocking the receptors to which angiotensin II binds. This prevents the vasoconstriction and aldosterone release triggered by angiotensin II, lowering blood pressure, reducing fluid overload, and protecting blood vessels and organs like the heart and kidneys. (4)
Common Losartan Side Effects
The most commonly reported side effects (occurring in at least 2% of patients) reported with losartan use include:
- Dizziness
- Upper respiratory infections, such as the common cold
- Persistent, dry cough
- Stuffy nose
- Back pain
Losartan can cause other mild side effects. Most times, these side effects can be easily managed, self-resolve within a few weeks as your body adapts to the medication, and don't require immediate medical attention. These may include:
- Abdominal pain
- Constipation
- Nausea and vomiting
- Headaches
- Sleep disturbances
- Sensitivity to sunlight
- Ringing in the ears
- Shortness of breath
- Fatigue
Serious Side Effects and Risks
More serious side effects can occur when taking losartan. Contact your healthcare provider immediately if you begin to experience any of the following symptoms after starting or increasing your dose of losartan:
- Hyperkalemia (High Potassium): nausea, muscle weakness, irregular heartbeat
- Severe Allergic Reaction: angioedema (deep swelling of the face, lips, tongue, throat, abdomen, arms, or legs), rash, hives
- Hypotension (Low Blood Pressure): dizziness, lightheadedness, fatigue, difficulty concentrating, blurred vision, fainting
- Anemia: fatigue, pale skin, rapid heartbeat with activity, headaches, cold hands and feet
- Kidney Dysfunction: urinating less often, swelling in your hands and feet, unexplained weight gain
Black Box Warning
Losartan carries an FDA black box warning that contraindicates its use in pregnancy. Taking losartan during pregnancy, particularly in the second and third trimesters, can lead to severe complications like reduced amniotic fluid (oligohydramnios), fetal injury, and fetal death.
If a patient plans to or becomes pregnant while taking the medication, the drug should be discontinued immediately.
Losartan and Drug Interactions
Taking losartan with certain medications can increase the risk of adverse reactions caused by drug interactions. Taking losartan with the following medications is not recommended:
- Aliskiren
- Potassium-sparing diuretics ("water pills"), including spironolactone, triamterene, and amiloride
- Angiotensin-converting enzyme (ACE) inhibitors, like enalapril or lisinopril
- Nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin, ibuprofen, and naproxen
- Lithium
This is not a complete list of possible drug interactions. Before taking losartan, give your doctor a full list of medications and supplements that you are currently taking.
Who Is at Higher Risk for Side Effects?
While losartan is generally well-tolerated, specific populations are more susceptible to experiencing side effects or complications when taking this medication.
Kidney Disease
Studies have shown that losartan can be safely administered in hypertensive patients with compromised renal function, but routine monitoring for hyperkalemia and renal function is important. Losartan should be discontinued if a decrease in kidney function is observed. (9)
The American College of Cardiology guidelines highlight an increased risk of hyperkalemia in patients with chronic kidney disease or those on potassium supplements or potassium-sparing drugs. Patients with severe bilateral renal artery stenosis have an increased risk of acute renal failure when they are treated with losartan.
Angioedema
Losartan should not be used in patients with a history of angioedema related to ARBs. However, patients with a history of angioedema with an ACE inhibitor can receive an ARB beginning six weeks after discontinuing the ACE inhibitor. (17)
Geriatric Patients
While studies have not demonstrated an increased risk of side effects that would limit use in elderly patients, older adults may have age-related physiological changes and practical considerations like polypharmacy (the use of multiple medications) that can increase their sensitivity to the drug's effects. These factors may heighten the risk of side effects such as dizziness, lightheadedness, and falls.
Liver Disease
Since losartan is metabolized in the liver, patients with significant liver disease may have a reduced ability to process the medication, leading to higher drug levels in the blood. This can increase the likelihood of side effects such as low blood pressure or elevated potassium levels. (10)
Managing and Preventing Side Effects
These strategies can help manage and prevent losartan's side effects:
Dietary Recommendations: Patients taking losartan should be mindful of their potassium intake. Since losartan can increase potassium levels in the blood, avoiding potassium-rich salt substitutes and high-potassium foods (like bananas, apricots, and potatoes) may help prevent hyperkalemia. A balanced, heart-healthy diet tailored to individual health needs, potentially guided by a dietitian, can reduce the risk of side effects and promote overall cardiovascular health.
Consulting Before Using Medications or Supplements: Patients should always consult their healthcare provider before adding new medications or supplements to their health routine to prevent drug interactions.
Dose Modifications: Losartan's dosage can be adjusted based on the patient's age, kidney or liver function, and overall health status. For instance, lower starting doses may be used in patients with impaired liver function or those prone to low blood pressure.
Regular Monitoring: Doctors should routinely measure blood pressure, kidney function, and potassium levels in patients taking losartan.
Alternative Drug Substitutes: For patients who cannot tolerate losartan due to significant side effects, alternative medications, like ACE inhibitors, may be considered. These medications have similar mechanisms of action but may have different side effect profiles.
When to Seek Medical Attention
While many of losartan's possible side effects are mild and will likely go away on their own, you should always talk to a doctor if they persist, worsen, or are particularly bothersome.
Red flags that require immediate action include:
- Severe dizziness
- Fainting
- Swelling
- Difficulty breathing
- Signs of acute kidney injury: decreased urine output, swelling in the lower extremities, flank pain, nausea or vomiting
Patient Education: Empowering Informed Decision-Making
Encouraging informed decision-making for losartan therapy involves empowering patients with knowledge about the drug's benefits and potential risks while utilizing clinical tools to guide personalized treatment decisions. This approach fosters collaboration between patients and healthcare providers, ensuring that the chosen therapy aligns with the individual's health goals and medical needs.
Clinical decision-making aids, like the ASCVD Risk Calculator, can support open communication and informed health decisions when weighing the pros and cons of pharmacotherapy and the overall impact of losartan on reducing cardiovascular risk.
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Key Takeaways
- While losartan is associated with potential side effects, including dizziness, elevated potassium levels, and rare instances of kidney impairment, it is widely regarded as a safe and effective first-line treatment for managing high blood pressure and reducing cardiovascular risks.
- Studies consistently demonstrate that losartan is generally well-tolerated, with low discontinuation rates due to adverse effects. The drug's benefits often outweigh its risks when prescribed and monitored appropriately, particularly for patients with conditions like hypertension, diabetes, or heart failure.
- Patients are encouraged to maintain open communication with their healthcare providers to ensure optimal outcomes. Regular monitoring of blood pressure, kidney function, and potassium levels, coupled with promptly reporting any new or worsening symptoms, supports medication safety and compliance.
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