St John's wort is the plant species Hypericum perforatum, also known as Tipton's Weed or Klamath weed, but, with qualifiers, 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 have been placed by some in the family Hypericaceae, but more recently have been included in the Clusiaceae. Approximately 370 species of the genus Hypericum exist worldwide with a native geographical distribution including temperate and subtropical regions of North America, Europe, Asia Minor, Russia, India, and China.

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 which 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. 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. The sepals are pointed, with glandular dots in the tissue. There are many stamens, which are united at the base into three bundles.

The word 'wort' is pronounced to rhyme with 'word' (not 'wart'). 'Wort' forms part of the name of many medicinal herbs, such as lungwort, woundwort, soapwort etc. St. John's wort is widely known as a herbal treatment for depression.

The plant is named after St John the Baptist, whose feast day, 24 June (midsummer), occurs when daylight in Europe is longest and the plant is in full bloom. Its five yellow petals resemble a halo, and its red sap symbolises the blood of the martyred saint.

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 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 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.

Although Hypericum perforatum is grown commercially in some regions of south east Europe, it is listed as a noxious weed in more than twenty countries and has introduced populations in South and North America, India, New Zealand, Australia, and South Africa. In pastures, St John’s wort acts as both a toxic and invasive weed. It replaces useful vegetation to the extent of making productive land unviable or acts as an alien species in natural ecosystems. Ingestion by livestock can cause photosensitization, central nervous system depression, spontaneous abortion, and can lead to death. In western North America three beetles Chrysolina quadrigemina, Chrysolina hyperici and Agrilus hyperici have been introduced as biocontrol agents.

St John's wort has been used as a folk medicine for hundreds of years, particularly for healing wounds. In medieval times, St John's wort was used for 'driving out the inner devil'. The philosopher Paracelcus (c1525) recommended it for hallucinations and 'dragons', as well as for healing wounds.

Nicholas Culpeper says of St. John’s Wort:

“It is a singular wound herb; boiled in wine and drank, it heals inward hurts or bruises; made into an ointment, it open obstructions, dissolves swellings, and closes up the lips of wounds. The decoction of the herb and flowers, especially of the seed, being drank in wine, with the juice of knot-grass, helps all manner of vomiting and spitting of blood, is good for those that are bitten or stung by any venomous creature, and for those that cannot make water. Two drams of the seed of St. John's Wort made into powder, and drank in a little broth, doth gently expel choler or congealed blood in the stomach.”

Its antibacterial properties were reported scientifically in 1959 and 1971, when the active antibacterial substance, called hyperforin, was extracted and analysed. It is also known to be effective for treating viral infections such as herpes. Extracts of St John's wort are made into capsules and other types of preparations which are used to treat depression. It recently became a popular treatment for depression.

St John's wort contains many different chemicals. Some are thought to be the active ingredients. How these chemicals actually work in the body is not clear. It is thought that they may alter the balance of some of the chemicals in the brain (neurotransmitters) such as serotonin, dopamine, gamma aminobutyric acid (GABA), and noradrenaline. Alterations in the balance of these neurotransmitters are thought to play some part in causing depression.

Tablets made using a standardised extract of St John's wort have been extensively researched in Germany since the early 1980s, and are now widely available from health food shops as a herbal remedy for mild to moderate depression. Research in America found it unhelpful for severe depression, but this has been questioned by more recent research which suggests that it compared favourably with paroxetine (a synthesised antidepressant) in moderate to severe depression.

A report in 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 which 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.

Standardized extracts are generally available over the counter, though in some countries (such as 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. There are products available combining St John's wort with other herbs, such as lemon balm (Melissa officianalis) and hops (Humulus lupulus), which are both sleep-inducing herbs. This combination would be suggested for people with depression who have difficulty sleeping. Like prescription antidepressants, it takes 2-4 weeks for the effect of St John's wort to build up fully.

St John's wort is an unlicensed herbal medicine, and there is no standardisation of preparations or dosage. The German trials appear to have used a daily dose of total extract, ranging from 0.4mg (400 micrograms) up to 1000mg (1 gram).

Preparations available in the UK often give a strength in terms of percentage hypericin, or hypericum extract, and the suggested dosage is 200mg to 1000mg of 0.3 per cent standardised hypericum extract per day, which is usually taken in two or three doses.

It is important to check the strength and follow the dosage recommendations of the product you are using, and to be aware that if you switch to a different product the strength may be different. Depending on the herbal composition of the product used, St John's wort may take effect more quickly than prescribed antidepressants.

It is not clear how well St John's wort works in depression. A recent systematic review of St John's Wort (that reviewed many research trials) concluded that ...

"Current evidence regarding hypericum extracts is inconsistent and confusing. In patients who meet criteria for major depression, several recent placebo-controlled trials suggest that the tested hypericum extracts have minimal beneficial effects while other trials suggest that hypericum and standard antidepressants have similar beneficial effects."

Possible risks
St John's wort sometimes reacts with other drugs. So:

• You should not take it if you are taking warfarin, cyclosporin, oral contraceptives, anticonvulsants, digoxin, theophylline, or certain anti-HIV drugs. This is because it may reduce the effect of these drugs.
• You should not take it at the same time as taking an SSRI antidepressant (selective serotonin reuptake inhibitor) or a triptan drugs used for migraine (such as sumatriptan). This is because it has an additive effect to these drugs which can cause problems.

The most common side-effects are dry mouth, dizziness, gut symptoms, increased sensitivity to sunlight, and tiredness. Also, you should not take St John's wort if you are pregnant or breastfeeding as it has not been proved to be safe in these situations.

Because of the uncertain effectiveness, possible side-effects, and possible interactions with other drugs, many doctors now do not recommend that St John's wort should be used. Also, if you have moderate or severe depression, it is generally best that you see a doctor who can advise on treatments and monitor your progress.

So, St John's wort may have some effect on easing depression in some cases. It may be worth a try if you have mild depression. However, if you have moderate or severe depression it is probably not appropriate to buy it 'over the counter'. Generally, you should see a doctor for advice on treatment if you have moderate or severe depression.