Minoxidil is an antihypertensive vasodilator medication. It also slows or stops hair loss and promotes hair regrowth. Now off-patent, it is available over-the-counter for the treatment of androgenic alopecia. Widely used for the treatment of hair loss, it has been proven clinically effective in both the prevention of loss and in establishing varying degrees of hair re-growth in males and females suffering pattern baldness. Minoxidil must be used indefinitely for continued support of existing hair follicles and the maintenance of any experienced hair regrowth. The mechanism by which minoxidil promotes hair growth is not fully understood. Minoxidil contains the nitric oxide chemical moiety and may act as a nitric oxide agonist. Similarly, minoxidil is a potassium channel opener, causing hyperpolarization of cell membranes. Minoxidil is less effective when there is a large area of hair loss.