Get emergency medical help if you have signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.
Call your doctor at once if you have:
a light-headed feeling, like you might pass out;
irregular heartbeats;
eye pain, vision problems;
kidney problems--little or no urination, rapid weight gain, swelling in your hands, feet, or ankles;
new or worsening symptoms of lupus--joint pain, and a skin rash on your cheeks or arms that worsens in sunlight; or
signs of an electrolyte imbalance--increased thirst or urination, confusion, vomiting, constipation, muscle pain, leg cramps, irregular heartbeats, numbness or tingling, severe weakness, loss of movement, feeling jittery or unsteady.
Common side effects may include:
dizziness;
back pain; or
cold symptoms such as stuffy nose, sneezing, sore throat.
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.
 Hydrochlorothiazide/losartan side effects (more detail)
