Phentolamine is indicated for the control of episodes of hypertension and sweating that occur with a disease called pheochromocytoma. If tachycardia is excessive, it may be necessary to use a beta-blocking agent concomitantly. Phentolamine is a long-acting, adrenergic, alpha-receptor blocking agent which can produce and maintain "chemical sympathectomy" by oral administration. It increases blood flow to the skin, mucosa and abdominal viscera, and lowers both supine and erect blood pressures. It has no effect on the parasympathetic system. Phentolamine works by blocking alpha receptors in certain parts of the body. Alpha receptors are present in the muscle that lines the walls of blood vessels. When the receptors are blocked by Phentolamine, the muscle relaxes and the blood vessels widen. This widening of the blood vessels results in a lowering of blood pressure.