Sclerotherapy is the most preferred method used by doctors to treat venous insufficiency. Sclerotherapy is a procedure that is used to treat blood vessels, venous insufficiency, and those of the lymphatic system. A chemical is injected into the vessels which make the damaged veins shrink. Sclerotherapy is an effective treatment to cure varicose veins and spider veins. Sclerotherapy causes infected veins to scar and reroutes the blood through other healthier veins.