St. John's wort (Hypericum perforatum) is claimed to treat several conditions, such as depression, obsessive-compulsive disorder, and migraines. St. John's wort is believed to work in a similar way as selective serotonin reuptake inhibitor (SSRI) antidepressants by increasing the levels of serotonin (a brain chemical). Some of the St. John's wort benefits are more credible than others. In addition, just because St. John's wort is a "natural" product, it does not automatically mean it is safe.
(Click Benefits of St. John's Wort to learn more about the conditions St. John's wort is claimed to treat, as well as detailed information on how it works to treat these conditions.)