Saint John's wort is the plant species Hypericum perforatum, and is also known as Tipton's weed, chase-devil, or Klamath weed. With qualifiers, St John's wort is used to refer to any species of the genus Hypericum. Therefore, H. perforatum is sometimes called common St John's wort to differentiate it. The species of Hypericum are classified in the Hypericaceae family, having previously been classified as Guttiferae or Clusiaceae. Approximately 370 species of the genus Hypericum exist worldwide with a native geographical distribution including temperate and subtropical regions of North America, Europe, Turkey, Russia, India, China and Brazil.
Hypericum perforatum is a yellow-flowering, stoloniferous or sarmentose, perennial herb indigenous to Europe, which has been introduced to many temperate areas of the world and grows wild in many meadows. The common name comes from its traditional flowering and harvesting on Saint John's day, 24 June. The genus name Hypericum is derived from the Greek words hyper (above) and eikon (picture), in reference to the traditional use of the plant to ward off evil, by hanging plants over a religious icon in the house during Saint John's day. The species name perforatum refers to the presence of small oil glands in the leaves that look like windows, which can be seen when they are held against the light. St John's wort is a perennial plant with extensive, creeping rhizomes. Its stems are erect, branched in the upper section, and can grow to 1 m high. It has opposing, stalkless, narrow, oblong leaves that are 12 mm long or slightly larger. The leaves are yellow-green in color, with transparent dots throughout the tissue and occasionally with a few black dots on the lower surface. Leaves exhibit obvious translucent dots when held up to the light, giving them a ‘perforated’ appearance, hence the plant's Latin name. Its flowers measure up to 2.5 cm across, have five petals, and are colored bright yellow with conspicuous black dots. The flowers appear in broad cymes at the ends of the upper branches, between late spring and early to mid summer. The sepals are pointed, with glandular dots in the tissue. There are many stamens, which are united at the base into three bundles. When flower buds (not the flowers themselves) or seed pods are crushed, a reddish/purple liquid is produced.
St John's wort is widely known as an herbal treatment for depression. In some countries, such as Germany, it is commonly prescribed for mild depression, especially in children and adolescents. A report from the Cochrane Review states: The available evidence suggests that the Hypericum extracts tested in the included trials a) are superior to placebo in patients with major depression; b) are similarly effective as standard antidepressants; and c) have fewer side-effects than standard antidepressants. There are two issues that complicate the interpretation of our findings: 1) While the influence of precision on study results in placebo-controlled trials is less pronounced in this updated version of our review compared to the previous version (Linde 2005a), results from more precise trials still show smaller effects over placebo than less precise trials. 2) Results from German-language countries are considerably more favourable for hypericum than trials from other countries. In one study, St John's wort was not found to be effective for patients suffering from dysthymia, a less severe and more chronic variety of depression.However, the distinction between mild depression and dysthymia is hazy, and St John's wort has been shown to be effective in the treatment of mild to moderate depression in many studies. Standardized extracts are generally available over the counter, though in some countries (such as the Republic of Ireland) a prescription is required. Extracts are usually in tablet or capsule form, and also in teabags and tinctures. Herbalists are more likely to use a fluid extract than a tincture. Hypericum was prescribed in ancient Greece, and it has been used ever since.