Losartan Side Effects: What to Expect and When to Act

Losartan is a common blood pressure medicine that many people tolerate well, but it can cause side effects. Knowing what’s normal and what needs medical attention helps you avoid problems. Below I’ll lay out the usual reactions, the serious risks, who should avoid it, and simple steps to stay safe.

Common and mild side effects

The most common complaints are dizziness or lightheadedness, especially after the first dose or when your dose is raised. Headache, fatigue, nasal congestion, and mild stomach upset can also occur. Unlike ACE inhibitors, losartan rarely causes a persistent dry cough, but some people still report coughing. These mild effects often fade after a few days to a few weeks.

Serious side effects and warning signs

Watch for signs that need prompt care. Severe dizziness, fainting, or feeling very weak can signal low blood pressure. Swelling of the face, lips, tongue, or throat may mean angioedema — a rare but dangerous reaction. Call emergency services if you have trouble breathing or significant swelling. Losartan can raise potassium levels; symptoms include muscle weakness, tingling, or an irregular heartbeat. It can also affect kidney function; a sudden drop in urine output or worsening swelling should be checked right away.

People with bilateral renal artery stenosis or severe kidney disease may see a big rise in creatinine after starting losartan. That’s why doctors often check kidney blood tests within 1–2 weeks of starting or increasing the dose.

Pregnancy is a strict no—losartan can harm a developing fetus. If you are pregnant or planning to become pregnant, tell your provider and stop the medicine under medical guidance.

Some drugs interact with losartan. Don’t mix it with potassium supplements, potassium-sparing diuretics, or salt substitutes containing potassium unless your doctor says it’s safe. NSAIDs like ibuprofen can reduce how well losartan lowers blood pressure and may worsen kidney function. Lithium levels can also rise when taken with losartan; careful monitoring is needed.

Dose-related effects matter: starting low and increasing slowly reduces dizziness and fainting risk. If you feel faint after a dose, sit or lie down and call your doctor. For minor side effects that don’t bother you, your doctor might simply monitor you or try a lower dose.

Simple steps to stay safe: take losartan at the same time daily, avoid sudden standing after sitting, limit potassium-rich foods if advised, and get blood tests for creatinine and potassium as recommended. Keep a list of all medicines and supplements to review for interactions.

If you’re unsure whether a symptom is from losartan, contact your healthcare provider — don’t stop the medicine suddenly without talking to them. Stopping abruptly can raise blood pressure quickly. With the right monitoring and a bit of caution, many people benefit from losartan with few problems.

Before you start, ask your prescriber: What dose is right for me? Do I need baseline blood tests for kidney function and potassium? How soon should I report dizziness or swelling? Are there safer options if I’m pregnant or have kidney artery issues? Keeping these questions handy makes appointments more productive and efficient.