Essiac tea is a combination of various herbs which has been used by some people as a 'natural' cancer treatment. To date, no well-controlled scientific studies have been performed to determine its effectiveness in either people or animals. The herbs included in the formula include burdock root, sheep sorrel, Turkish rhubarb root, slippery elm bark, and sometimes red clover, kelp, watercress, or blessed thistle. There are several manufacturers of this product, which is much more common in Canada than in the United States. In humans, it is most commonly used as an adjunct to conventional cancer therapy.