Sclerotherapy is highly effective in most cases. Reports indicate that anywhere from 50% to up to 80% of treated veins vanish within six months of treatment. Sclerotherapy provides long-lasting relief from unsightly veins by permanently removing them as the medication runs its course. However, the treatment is not a permanent fix for spider veins and varicose veins altogether. Often, the appearance of unwanted veins at the surface of the skin is an ongoing problem. So, new veins may form after the treated ones have faded.