No individual herb is considered especially useful for promoting fertility. Rather, more than 150 different herbs, usually given in complex formulas comprised of 15 or more ingredients according to practicioners, are used in the treatment of infertility with the purpose of correcting a functional or organic problem that caused infertility. The design of the formulas has varied somewhat over the centuries, based on prevailing theories and available resources, and individual practitioners have a preference for particular herbs, thus accounting for some of the variations among formulas that are recommended. However, differences among individuals being treated accounts for the greatest variation in the selection of herbs and formulas to be used. There are some “exotic” materials that are frequently found in fertility formulas, such as deer antler and sea horse, but the prominent materials are derived from roots, barks, leaves, flowers, and fruits. Formulas for men and for women tend to be different, but there is considerable overlap in the ingredients used.