Why St John’s wort is known for its medicinal uses

The generic name Hypericum for St John’s wort derives from the Greek word hyper-ikon or hyper-eikon (“above image”), with some authors suggesting this meant the herb was hung above painted icons or shrines to drive away evil influences. Historically, St John’s wort was believed to protect houses from lightning and to have the power to repel witches, ghosts and demons: a Latin name for the plant used by medieval herbalists was Euga daemonum, or “flight of demons”.

Before sunrise on St John’s Eve (June 23) was considered the most important time to gather the herb, and festive fires were lit in the evening in honour of St John the Baptist, with the smoke used to purify the herbs, livestock and people. The collected St John’s wort was hung above doorways and cattle stalls, serving to ward off any witch or evil spirit.

An old common name, fairy herb, is reflected in folklore from the Isle of Man that said stepping on the plant would result in being carried away by the “wee folk”. Clearly, treading on this medicinal herb was best avoided, as another folk legend from the Isle of Wight warns of a phantom horse appearing from the roots, which would rise up and gallop into the night, transporting the person who inadvertently trod on the plant after dark far from home.

Another legend from the Scottish Highlands tells of St Columba (521–597 CE) using St John’s wort to cure a young shepherd of insanity, brought on from spending too much time alone on the hillsides. St Columba is said to have applied the herb under the armpit or groin area of the shepherd, giving rise to its Gaelic name that translates as “St Columba’s oxterful”.

H. perforatum can grow up to 1m (3ft) high with its reddish stem branching near the top and bearing clusters of bright yellow, star-shaped flowers. The flowers have five (rarely four) petals and sepals with numerous stamens, which are joined at the base into bundles. The yellow petals have conspicuous black dots along the margins. The oblong-shaped leaves are 1–2cm long, opposite and with small translucent oil glands that appear as the characteristic “perforations” when held up to the light. The plant has extensive creeping rhizomes, sending roots and shoots along their length. St John’s wort is self-fertile and spreads rapidly, growing both vegetatively and sexually; after pollination by bees and other insects, a single plant may produce 100,000 seeds per year, which can remain viable in the soil for decades. It is considered a noxious weed in several countries outside of its native range, and it can poison livestock.

Red, yellow and brown coloured dyes can be obtained from H. perforatum, depending on the extract method. Hypericin is a notable pigment found in the plant, responsible for the red colour of the plant’s extract, which is said to resemble blood.

Belief in the Doctrine of Signatures became popular during the medieval period, whereby it was thought that plants resembling the body part or ailment were signs from God to indicate their use. The red juice from H. perforatum and the perforations in the leaves symbolised the blood and holy wounds of St John the Baptist’s martyrdom, while the cross formed by the leaves when looked at from above only added to the plant’s symbolic association.

It is perhaps no surprise, then, that one of the traditional uses of St John’s wort was in treating wounds—as an astringent herb it was applied to scratches and wounds to staunch bleeding. John Parkinson (1567–1650), the apothecary to James I, said that it was “a singular wound herb as any other” and could be drunk boiled in wine, or prepared into oil or ointment for topical use. Both Parkinson and the herbalist Nicholas Culpeper (1616–54) suggested St John’s wort could be used to “dissolve” tumours or swellings. Culpeper recommended a decoction of the herb and flowers taken in wine, or the seed ground into a powder, for use in the treatment of internal bleeding caused by a burst vein, bruises or falls.

Several other uses of St John’s wort were outlined by Culpeper including against bites and stings, a decoction of seeds for sciatica, epilepsy and palsy, and a decoction of leaves and seeds to be drunk for “ague fits”, which were fever-chills—a characteristic symptom of malaria. In bygone days in rural areas of Britain, Hypericum was taken as an infusion to treat bed-wetting in children and the elderly, and for coughs or catarrh. It was also said to make hair grow. Topically, it was used to treat burns, bed sores and for healing fractures and sprains.

Historically, a tincture of St John’s wort flowers in spirit of wine was said to ward off melancholia; today it is best known for its use in treating low mood and mild depression. The use of Hypericum in treating mild cases of depression and nervous conditions was popular in Ireland, where it was also used to treat gangrene, inflammation, diarrhoea, dysentery and intestinal worms.

In addition to its medicinal uses, St John’s wort flowers can be used in making mead, and the herb can also be steeped in hot water to make a soothing tea.