Losartan’s most common side effects are usually mild and often improve as your body gets used to the medicine.

Quick Scoop: Most common side effects

The side effects people report most often with losartan include:

  • Dizziness or lightheadedness, especially when standing up
  • Fatigue or feeling unusually tired
  • Headache
  • Stuffy or runny nose, nasal congestion
  • Upper respiratory infections (like common cold–type symptoms)
  • Back pain or joint pains
  • Mild digestive issues: nausea, vomiting, diarrhea, stomach or abdominal discomfort
  • Muscle or joint aches
  • Mild swelling from fluid retention or puffiness
  • Cough (less common than with ACE inhibitors, but still reported)

These effects are generally considered mild and often manageable, but you should tell your doctor if they are new, severe, or not going away.

Less common but important to know

While not “most common,” doctors also watch for these because they can be more serious:

  • Drop in blood pressure (you might feel faint, very dizzy, or weak)
  • High potassium levels (can cause muscle weakness, irregular heartbeat)
  • Worsening kidney function or kidney failure
  • Allergic reactions or angioedema (swelling of face, lips, tongue, or throat, trouble breathing)

If you notice swelling of the face or tongue, difficulty breathing, chest tightness, or you completely pass out, that’s an emergency and needs urgent medical attention.

A quick story-style example

Imagine someone who just started losartan for high blood pressure. In the first week, they notice they feel a bit dizzy when they stand up quickly and have a mild headache and stuffy nose. They sit up slowly in the morning, drink enough fluids, and the dizziness eases over a few days. But if their dizziness became so strong they nearly blacked out, or if they noticed swelling of their lips or tongue, that would be the point to seek urgent care instead of waiting.

When to call your doctor

Contact your doctor soon (non‑emergency) if:

  • Dizziness, fatigue, or headaches are persistent or getting worse
  • You notice new swelling in the legs or ankles
  • You have ongoing nausea, vomiting, or diarrhea affecting your ability to eat or drink
  • You see changes in urination (much less than usual or dark urine)

Get emergency help if:

  • Your lips, tongue, face, or throat swell
  • You have trouble breathing or chest tightness
  • You faint or feel like you’re about to faint and can’t stay upright
  • You have severe chest pain or sudden severe headache, confusion, or trouble speaking

Quick FAQ style notes

  • Are most people able to stay on losartan?
    • Yes, most people tolerate it well, and many only have mild or no side effects.
  • Is losartan safe in pregnancy?
    • No. It carries a boxed warning for risk of serious harm to an unborn baby and should not be used during pregnancy.
  • Do side effects mean I should stop it on my own?
    • Do not stop it suddenly without medical advice; talk to your prescriber first so they can adjust dose or switch medications safely.

This information is general and not a substitute for care from your own doctor. Always check with a healthcare professional about symptoms or medication changes.

TL;DR: The most common side effects of losartan are dizziness, fatigue, headache, cold‑like symptoms, nasal congestion, and back or joint pain; serious problems like kidney issues, very low blood pressure, high potassium, or facial/tongue swelling are less common but need urgent evaluation if they occur.

Information gathered from public forums or data available on the internet and portrayed here.