Other names for St John's wort include Tipton's weed, rosin rose, goatweed, chase-devil, or Klamath weed. In common speech, the name St John's wort may be used to refer to any species of the genus Hypericum. Therefore, H. perforatum is sometimes called Common St John's wort or Perforate St John's wort in order to differentiate it.
Hypericum perforatum is a yellow-flowering, stoloniferous or sarmentose, perennialherb indigenous to Europe. It has been introduced to many temperate areas of the world and grows wild in many meadows. The herb's common name comes from its traditional flowering and harvesting on St John's day, 24 June. The genus name Hypericum is derived from the Greek words hyper (above) and eikon (picture), in reference to the plant's traditional use in warding off evil by hanging plants over a religious icon in the house during St 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. The pollen grains are ellipsoidal.
When flower buds (not the flowers themselves) or seed pods are crushed, a reddish/purple liquid is produced.
St John's wort reproduces both vegetatively and sexually. It thrives in areas with either a winter- or summer-dominant rainfall pattern; however, distribution is restricted by temperatures too low for seed germination or seedling survival. Altitudes greater than 1500 m, rainfall less than 500 mm, and a daily mean January (in Southern hemisphere) temperature greater than 24 degrees C are considered limiting thresholds. Depending on environmental and climatic conditions, and rosette age, St John's wort will alter growth form and habit to promote survival. Summer rains are particularly effective in allowing the plant to grow vegetatively, following defoliation by insects or grazing.
The seeds can persist for decades in the soil seed bank, germinating following disturbance.
St John's wort is widely known as a herbal treatment for depression. In some countries, such as Germany, it is commonly prescribed for mild to moderate depression, especially in children and adolescents. Specifically, Germany has a governmental organization called Commission E which regularly performs rigorous studies on herbal medicine. It is proposed that the mechanism of action of St. John's wort is due to the inhibition of reuptake of certain neurotransmitters. The best studied chemical components of the plant are hypericin and pseudohypericin.
An analysis of twenty-nine clinical trials with more than five thousand patients was conducted by Cochrane Collaboration. The review concluded that extracts of St John's wort were superior to placebo in patients with major depression. St John's wort had similar efficacy to standard antidepressants. The rate of side-effects was half that of newer SSRI antidepressants and one-fifth that of older tricyclic antidepressants. 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.
Other medical uses
St John's wort is being studied for effectiveness in the treatment of certain somatoform disorders. Results from the initial studies are mixed and still inconclusive; some research has found no effectiveness, other research has found a slight lightening of symptoms. Further study is needed and is being performed.
A major constituent chemical, hyperforin, may be useful for treatment of alcoholism, although dosage, safety and efficacy have not been studied. Hyperforin has also displayed antibacterial properties against Gram-positive bacteria, although dosage, safety and efficacy has not been studied.Herbal medicine has also employed lipophilic extracts from St John's wort as a topical remedy for wounds, abrasions, burns, and muscle pain. The positive effects that have been observed are generally attributed to hyperforin due to its possible antibacterial and anti-inflammatory effects. For this reason hyperforin may be useful in the treatment of infected wounds and inflammatory skin diseases. In response to hyperforin's incorporation into a new bath oil, a study to assess potential skin irritation was conducted which found good skin tolerance of St John's wort.
A randomized controlled trial of St John's wort found no significant difference between it and placebo in the management of ADHD symptoms over eight weeks. However, the St John's wort extract used in the study, originally confirmed to contain 0.3% hypericin, was allowed to degrade to levels of 0.13% hypericin and 0.14% hyperforin. Given that the level of hyperforin was not ascertained at the beginning of the study, and levels of both hyperforin and hypericin were well below that used in other studies, little can be determined based on this study alone. Hypericin and pseudohypericin have shown both antiviral and antibacterial activities. It is believed that these molecules bind non-specifically to viral and cellular membranes and can result in photo-oxidation of the pathogens to kill them.
A research team from the Universidad Complutense de Madrid (UCM) published a study entitled "Hypericum perforatum. Possible option against Parkinson's disease", which suggests that St John's wort has antioxidant active ingredients that could help reduce the neuronal degeneration caused by the disease.
Recent evidence suggests that daily treatment with St John's wort may improve the most common physical and behavioural symptoms associated with premenstrual syndrome.
St John's wort alleviated age-related long-term memory impairment in rats.
Adverse effects and drug interactions
St John's wort is generally well tolerated, with an adverse effect profile similar to placebo. The most common adverse effects reported are gastrointestinal symptoms, dizziness, confusion, tiredness and sedation. It also decreases the levels of estrogens, such as estradiol, by speeding up its metabolism, and should not be taken by women on contraceptive pills as it upregulates the CYP3A4 cytochrome of the P450 system in the liver.
St John's wort may rarely cause photosensitivity. This can lead to visual sensitivity to light and to sunburns in situations that would not normally cause them. Related to this, recent studies concluded that the extract reacts with light, both visible and ultraviolet, to produce free radicals, molecules that can damage the cells of the body. These can react with vital proteins in the eye that, if damaged, precipitate out, causing cataracts. Another study found that in low concentrations, St. John's wort inhibits free radical production in both cell-free and human vascular tissue, revealing antioxidant properties of the compound. The same study found pro-oxidant activity at the highest concentration tested.
Consumption of St. John's wort is discouraged for those with bipolar disorder. There is concern that people with major depression taking St. John’s wort may be at a higher risk for mania.
While St. John's wort shows some promise in treating children, it is advised that it is only done with medical supervision. 
St John's wort has been shown to cause multiple drug interactions through induction of the cytochrome P450 enzymes CYP3A4 and CYP2C9, and CYP1A2 (females only). This drug-metabolizing enzyme induction results in the increased metabolism of certain drugs, leading to decreased plasma concentration and potential clinical effect. The principal constituents thought to be responsible are hyperforin and amentoflavone.
St John's wort has also been shown to cause drug interactions through the induction of the P-glycoprotein (P-gp) efflux transporter. Increased P-gp expression results in decreased absorption and increased clearance of certain drugs, leading to lower plasma concentration and potential clinical efficacy.
Examples of drugs causing clinically significant interactions with St John's wort
Hypericin, pseudohypericin, and hyperforin may be quantitated in plasma as confirmation of usage and to estimate the dosage. These three active substituents have plasma elimination half-lives within a range of 15–60 hours in humans. None of the three has been detected in urine specimens.
The naphthodianthrones hypericin and pseudohypericin along with the phloroglucinol derivative hyperforin are thought to be among the numerous active constituents. It also contains essential oils composed mainly of sesquiterpenes.
Selected chemical constituents of Hypericum perforatum
Serves as a TRPC6 and PXR agonist. Reuptake inhibitor of 5-HT (205nM), DA (102nM), NE (80nM), GABA (184nM), Glu (829nM), Gly and Ch (8.5μM). Angiogenesis, COX-1 (300nM), 5-LO (90nM), SIRT1 (15μM), SIRT2 (28μM) and MRSA (1.86μM) inhibitor.
Inhibits the following: inflammation (via NF-κB and STAT1 inhibition), cancer, HDAC, bacteria, viruses, protozoa and fungi. It is also known to prevent cardiovascular disease and cancer.
Has anti-cancer, anti-inflammatory, anti-allergic, anti-asthmatic, antihypertensive, analgesic, neuroprotective, gastroprotective, anti-diabetic, cardiovascular disease-preventing, antioxidant, antidepressant-like (in rat models of depression), anxiolytic-like, sedative, antimicrobial and athletic performance-promoting effects. Non-selective PDE1-4 inhibitor that is slightly selective for PDE3/4 over PDE1/2.
Partition coefficient. These values are experimental values taken from ChemSpider and  (the access dates are both 13–15 December 2013) where available or, if they are not available approximations are taken from [www.chemaxon.com/download/marvin/for-end-users/ ChemAxon MarvinSketch] 6.1.4 & 
^Values given in brackets are IC50/EC50 depending on whether it's an inhibitory or inductive action the compound displays towards the biologic target in question. If it pertains to bacterial growth inhibition the value is MIC50
^Depends on the time frame: short-term administration causes inhibition; long-term causes induction via PXR
In large doses, St John's wort is poisonous to grazing livestock (cattle, sheep, goats, horses). Behavioural signs of poisoning are general restlessness and skin irritation. Restlessness is often indicated by pawing of the ground, headshaking, head rubbing, and occasional hindlimb weakness with knuckling over, panting, confusion, and depression. Mania and hyperactivity may also result, including running in circles until exhausted. Observations of thick wort infestations by Australian graziers include the appearance of circular patches giving hillsides a ‘crop circle’ appearance, it is presumed, from this phenomenon. Animals typically seek shade and have reduced appetite. Hypersensitivity to water has been noted, and convulsions may occur following a knock to the head. Although general aversion to water is noted, some may seek water for relief.
Severe skin irritation is physically apparent, with reddening of non-pigmented and unprotected areas. This subsequently leads to itch and rubbing, followed by further inflammation, exudation, and scab formation. Lesions and inflammation that occur are said to resemble the conditions seen in foot and mouth disease. Sheep have been observed to have face swelling, dermatitis, and wool falling off due to rubbing. Lactating animals may cease or have reduced milk production; pregnant animals may abort. Lesions on udders are often apparent. Horses may show signs of anorexia, depression (with a comatose state), dilated pupils, and injected conjunctiva.
Increased respiration and heart rate is typically observed while one of the early signs of St John's wort poisoning is an abnormal increase in body temperature. Affected animals will lose weight, or fail to gain weight; young animals are more affected than old animals. In severe cases death may occur, as a direct result of starvation, or because of secondary disease or septicaemia of lesions. Some affected animals may accidentally drown. Poor performance of suckling lambs (pigmented and non-pigmented) has been noted, suggesting a reduction in the milk production, or the transmission of a toxin in the milk.
Most clinical signs in animals are caused by photosensitisation. Plants may induce either primary or secondary photosensitisation:
primary photosensitisation directly from chemicals contained in ingested plants
secondary photosensitisation from plant-associated damage to the liver.
Araya and Ford (1981) explored changes in liver function and concluded there was no evidence of Hypericum-related effect on the excretory capacity of the liver, or any interference was minimal and temporary. However, evidence of liver damage in blood plasma has been found at high and long rates of dosage.
Photosensitisation causes skin inflammation by a mechanism involving a pigment or photodynamic compound, which when activated by a certain wavelength of light leads to oxidation reactions in vivo. This leads to lesions of tissue, particularly noticeable on and around parts of skin exposed to light. Lightly covered or poorly pigmented areas are most conspicuous. Removal of affected animals from sunlight results in reduced symptoms of poisoning.
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