Used primarily to treat high blood pressure caused by pheochromocytoma, a tumor of the adrenal gland. It helps block the effects of certain hormones like norepinephrine, which can cause blood vessels to constrict. This action leads to dilation of blood vessels and reduced blood pressure. Also utilized in research settings to study blood flow and erectile dysfunction. Sometimes applied to reverse local anesthetic effects that cause tissue blanching due to vasoconstriction. Administered in ophthalmology to reduce intraocular pressure in certain glaucoma cases.