In phytopharmaceutical or herbal medicine, the active ingredient may be either unknown or may require cofactors in order to achieve therapeutic goals. This leads to complications in labelling. One way manufacturers have attempted to indicate strength is to engage in standardization to a marker compound. Standardization has not been achieved yet, however, with different companies using different markers, or different levels of the same markers, or different methods of testing for marker compounds. For example, St John's wort is often standardized to the hypericin that is now known not to be the "active ingredient" for antidepressant use.  Other companies standardize to hyperforin or both, ignoring some 24 known additional possible active constituents. Many herbalists believe that the active ingredient in a plant is the plant itself.