Get emergency medical help if you have signs of an allergic reaction to doxazosin: 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;
severe ongoing stomach pain or bloating;
new or worsening chest pain;
trouble breathing; or
a penis erection that is painful or lasts 4 hours or longer.
Common doxazosin side effects may include:
low blood pressure, dizziness;
drowsiness;
headache; or
feeling weak or tired.
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.
 Doxazosin side effects (more detail)
