Losartan is a prescription drug used most commonly to treat high blood pressure (hypertension). It is sold as a generic and under the brand name Cozaar. Approved in its generic formulation by the FDA in 2010, Losartan is an angiotensin receptor blocker (ARB) that helps treat hypertension by widening the blood vessels. It is sometimes prescribed to treat diabetic kidney disease or congestive heart failure.

Losartan's most common side effects include upper respiratory infection, dizziness, blurred vision, back pain, diarrhoea, nausea and fatigue. Patients with existing medical conditions may experience more severe side effects.

Losartan can have a negative interaction with several prescription medicines. In many cases the interaction can worsen side effects. Because losartan is frequently prescribed for use in conjunction with other drugs to treat hypertension, your doctor may decide that the drugs' benefits outweigh the side effects.

A 2010 UK study published in "The Lancet Oncology" suggested that ARBs such as losartan are linked to a moderately increased risk of cancer. The researchers analysed previous data on about 60,000 patients and found a 1 per cent higher occurrence of cancer in patients taking ARBs. The study recommended further research to explore the apparent link.