More than 40 million people in the United States suffer from painful, ropy, bulging varicose veins. Varicose veins occur when the valves inside a vein become weakened or damaged. This causes blood to flow backward and pool inside the vein, which causes swelling. Varithena® is a sterile injectable foam used to treat varicose veins in the great saphenous vein (GSV) system. The great saphenous vein is the longest vein in the body, running along the length of the leg, returning blood from the foot.