Get emergency medical help if you have any of these signs of an allergic reaction to losartan: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
In extremely rare cases, losartan can cause a condition that results in the breakdown of skeletal muscle tissue, leading to potential kidney failure. Call your doctor right away if you have unexplained muscle pain, tenderness, or weakness especially if you also have fever, unusual tiredness, and dark colored urine.
Call your doctor at once if you have:
a feeling that you might pass out;
pain or burning when you urinate;
pale skin, feeling light-headed or short of breath, rapid heart rate, trouble concentrating;
wheezing, chest pain;
drowsiness, confusion, mood changes, increased thirst, loss of appetite, nausea and vomiting;
swelling, weight gain, feeling short of breath, urinating less than usual or not at all; or
high potassium (slow heart rate, weak pulse, muscle weakness, tingly feeling).
Common losartan side effects may include:
cold or flu symptoms such as stuffy nose, sneezing, sore throat, fever;
dry cough;
muscle cramps;
pain in your legs or back;
stomach pain, diarrhea;
headache, dizziness;
tired feeling; or
sleep problems (insomnia).
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
 Losartan side effects (more detail)
