Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Call your doctor at once if you have:
chest pain or pressure, pain spreading to your jaw or shoulder;
fast or pounding heartbeats;
a light-headed feeling, like you might pass out;
numbness, tingling, or burning pain in your hands or feet;
painful or difficult urination;
little or no urination; or
lupus-like syndrome--joint pain or swelling with fever, swollen glands, muscle aches, chest pain, vomiting, unusual thoughts or behavior, and patchy skin color.
Common side effects may include:
chest pain, fast heart rate;
headache; or
nausea, vomiting, diarrhea, loss of appetite.
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.
 Hydralazine side effects (more detail)
