Prazosin

Get emergency medical help if you have any of these 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 serious side effect such as:

fast or pounding heartbeats or fluttering in your chest;

feeling like you might pass out;

trouble breathing;

swelling in your hands, ankles, or feet; or

penis erection that is painful or lasts 4 hours or longer.

Less serious side effects may include:

mild dizziness;

weakness, tired feeling, drowsiness;

headache; or
nausea.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.