The Hypericum, commonly known as St. John's Wort, is a perennial semi-evergreen medicinal plant belonging to the family Clusiaceae (Guttiferae) and the genus Hypericum. It has been part of traditional medicine due to its herbal properties, particularly its antidepressant and antiviral effects. Its use as a medicinal herb dates back to ancient times, with references found in writings from many centuries ago. Although already known in ancient medicine (mentioned by Dioscorides, Galen, Pliny the Elder, and Mattioli), its most interesting use as an antidepressant was a relatively recent discovery: numerous studies have demonstrated its effectiveness, especially in cases of mild and moderate depression, with effects comparable to some antidepressant medications.

A review of studies conducted by the Cochrane Collaboration, one of the most authoritative scientific institutions in the world, in 2008 concluded that "current evidence suggests that Hypericum extracts are superior to placebo in the treatment of major depression, with a similar effectiveness to classical antidepressant drugs but with significantly fewer side effects." A review of studies published in 2016 came to the same conclusion, but also highlighted that the reporting and monitoring of side effects are less strict compared to common medications. Therefore, despite being in use for centuries, its long-term safety has not been extensively studied.

St. John's Wort is particularly widely used in Germany, where it is recommended as a treatment for depression in adolescents before attempting pharmacological options. Sometimes, it is also used in combination with other products for the herbal treatment of certain forms of anxiety.

The antidepressant mechanism of its active ingredients is only now beginning to be elucidated and appears to be only partially related to that of the most commonly used drugs today. Initially, hypericin was thought to be the active compound, but recent developments have clarified that other compounds present in the extracts also contribute synergistically to its effectiveness. These compounds include naphthodianthrones, primarily hypericin, pseudo-hypericin, isophycin, and proto-hypericin. They are photosensitive and probably responsible for the photosensitizing action of the extracts, with an average concentration of 0.2-0.3%. Additionally, there are phloroglucinols, such as hyperforin, another major active component, and its analogs, along with other lipophilic compounds. Hyperforin is unstable both in the presence of oxygen and light. Flavonoids, including amentoflavone, quercetin, lutein, hyperin, and others, are present in the extracts at an average concentration of 7-12%. Other compounds with probable synergistic pharmacodynamic and pharmacokinetic effects (tannins, xanthans, phenolic compounds, polysaccharides) are also present. The extracts also have remarkable antioxidant and neuroprotective properties, as well as improvement of vascular properties, which have suggested their use in some neurological pathologies. For these properties, researchers argue that Hypericum extracts should be a first-line treatment for depression in the elderly with high oxidative stress.

In traditional medicine, Hypericum is used as an antiseptic. Some of these uses are partly due to the antibacterial and antiviral properties of hyperforin, which can inhibit the growth of Gram-positive bacteria (but not Gram-negative), particularly strains resistant to other antibiotics. In traditional phytotherapy, the astringent, anti-inflammatory, and antibacterial qualities of Hypericum have been emphasized, both for internal and external use, especially in the treatment of burns, wounds, and sores. For this purpose, it is prepared as "Hypericum oil," an oleolite with a characteristic red color, obtained by macerating the plant in olive oil in the sun for 6-7 days.