Losartan: what it does and what to watch
Also known as: Losartan potassium · ARB, angiotensin receptor blocker (blood pressure medicine) · Updated 2026-08-19 · Educational — not medical advice
In plain language: Losartan blocks the same angiotensin II receptor that telmisartan does, preventing blood vessels from being squeezed narrow and reducing salt and water retention. One quirk of losartan is that the tablet itself is only partly active; the liver converts a portion of each dose into a stronger active form, which is part of why it's usually taken once daily.
What it's used for
- High blood pressure
- Protecting kidney function in people with diabetes
- Reducing stroke risk in people with high blood pressure and heart strain
Common side effects
- Dizziness
- Fatigue
- Mild dry cough (less common than with ACE inhibitors)
- Stuffy nose
- Back or muscle pain
Get medical help if…
Muscle weakness or irregular heartbeat (possible high potassium)
Reduced urination or swelling in the legs (possible kidney effect)
Swelling of the face, lips, tongue, or throat
Fainting or severe lightheadedness
Lab values it can move
Few guides tell you this part: medicines show up in blood work. If you take Losartan and a value below looks off on your report, this may be part of the story — never stop a medicine without your doctor.
Because losartan reduces the kidney's usual potassium-clearing signal, potassium is periodically checked to catch any gradual rise before it affects heart rhythm.
PotassiumCreatinine is tracked as a marker of kidney filtering function, since losartan changes the pressure inside the kidney's blood vessels in a way that's usually protective but occasionally needs monitoring.
CreatinineGood to know
- Kidney function and potassium are usually rechecked a few weeks after starting or adjusting the dose
- Avoided during pregnancy due to risks to a developing baby
- People with liver impairment may process this medicine differently, which a doctor accounts for
- Dehydration increases the chance of a bigger-than-expected drop in blood pressure
- Salt substitutes containing potassium are best discussed with a doctor first
Questions people ask
Is losartan the same as telmisartan?
They're both angiotensin receptor blockers that work the same general way, relaxing blood vessels by blocking the same hormone receptor, but they differ in how long their effects last and how the body processes them. Losartan needs to be converted by the liver into its active form, while telmisartan is active as taken. A doctor chooses between them based on other health factors.
Why does losartan cause less cough than some other blood pressure medicines?
A dry, persistent cough is a well-known side effect of a related but different class called ACE inhibitors, caused by a buildup of a substance called bradykinin. Losartan works one step further along the same pathway, blocking the angiotensin receptor directly rather than the enzyme upstream, which mostly avoids that bradykinin buildup and explains why cough is much less common with it.
What happens if potassium rises while on losartan?
A mild rise is common and usually harmless, but a more significant increase can cause muscle weakness, tingling, or irregular heartbeat, since potassium is important for how heart muscle cells conduct electrical signals. This is why periodic blood tests are used to catch a rising trend early, especially in people with reduced kidney function or those also taking potassium supplements.
Taking Losartan? See what your blood work says.
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