Cozaar (Losartan): Uses, Kidney Monitoring and Interactions

What this medicine treats

Cozaar contains losartan potassium, an angiotensin receptor blocker, or ARB. It lowers blood pressure by blocking angiotensin II activity. The US tablet label also covers selected patients with diabetic kidney disease and certain patients with hypertension and an enlarged left ventricle. This profile concerns the 50 mg oral tablet, not a combination tablet containing a diuretic. Indications can differ between countries.

Why follow-up matters

People commonly need long-term treatment, including when blood pressure causes no symptoms. A clinician checks blood pressure and blood tests to assess kidney function and potassium. The response cannot be judged only by how someone feels. Follow the directions for the prescribed product and discuss difficulties taking it with a pharmacist. Kidney disease, vomiting, diarrhoea or dehydration are important to report because the treatment plan may need review.

Side effects and urgent problems

Dizziness can occur, particularly when standing. Avoid driving if it affects you. Too much blood-pressure lowering may cause severe light-headedness or fainting. Losartan can increase potassium or worsen kidney function in susceptible people. An irregular heartbeat, marked weakness, much less urine, or persistent illness needs medical assessment. Sudden swelling of the face, tongue or throat with breathing difficulty is an emergency; rare serious allergic reactions can occur.

Interactions to check before adding a medicine

Potassium supplements, potassium-containing salt substitutes and potassium-sparing diuretics can increase the risk of high potassium. NSAID painkillers can impair kidney function and weaken the blood-pressure effect, especially during dehydration or kidney disease. Lithium levels can rise. Combining losartan with other medicines acting on the renin-angiotensin system can increase kidney, potassium and low-blood-pressure problems; aliskiren with Cozaar is contraindicated in diabetes in the US label. Ask for a complete medicine-list review rather than treating these combinations as interchangeable.

Pregnancy, breastfeeding and source scope

Losartan carries a US boxed warning for fetal harm. Known or suspected pregnancy needs immediate contact with the prescriber so treatment can be changed promptly and appropriately. It is not a pregnancy blood-pressure treatment. Human breastfeeding information is inadequate, so the medicine and feeding plan need individual review. This summary uses the US Cozaar label and general NHS patient guidance; local approved uses and precautions may differ.

Sources

• Cozaar oral tablets: US product information — US prescribing information revised June 2025; SPL version 9, effective 20 January 2026
• NHS guidance on losartan — Patient medicine guidance; checked 30 October 2026

Source check: 30 October 2026. This records a source check, not a clinical review by a doctor or pharmacist. Use the current leaflet supplied with your medicine and seek qualified advice for personal treatment.