St. John's Wort: Benefits, Uses, and Side Effects of This Medicinal Plant

St. John's Wort (Hypericum perforatum), also called common or perforate St. John's Wort, is a perennial medicinal herb best known today for its traditional use in wound healing and its modern reputation as a natural remedy for mild depression. The plant grows wild across meadows, forest edges, sparse oak and birch groves, scrubland, the margins of fields, and shelterbelts, and it is the single species from a large genus that has earned a place in official medicine.

Of the large family of Hypericum plants — and the genus counts more than 50 species — only Hypericum perforatum is classed among medicinal plants and used in official medicine. Below, this guide covers what St. John's Wort is, its botany and chemistry, how it acts on the body, the clinical evidence for depression, and the safety concerns and drug interactions that lead many doctors to advise caution.

What is St. John's Wort? Botanical description

St. John's Wort is a perennial herb reaching up to one metre tall, with one or several erect cylindrical stems bearing two raised longitudinal ridges and branching in the upper portion. The leaves are oblong to elliptical, up to three centimetres long and one and a half centimetres wide, dotted with translucent oil glands scattered across the leaf surface — the "perforated" look that gives perforatum its name.

The flowers of St. John's Wort are golden-yellow, up to three centimetres in diameter, and gathered in corymb-like or broadly paniculate clusters at the tips of the stem and shoots. Each flower has five petals, often edged with tiny black dots. Flowering and reproduction occur chiefly in midsummer; the plant sets large numbers of small seeds that disperse readily, which is why Hypericum perforatum has become an invasive weed of pastures in places such as Australia, where it is studied at institutions including the University of Adelaide.

The root system is a branched taproot that anchors the plant and lets it regrow from the crown each year, contributing to its persistence in the wild.

Scientific classification and related Hypericum species

St. John's Wort belongs to the genus Hypericum, placed in the family Hypericaceae (historically treated within Clusiaceae). The genus Hypericum is large and diverse, and several relatives are grown or noted for different reasons: Hypericum maculatum and H. attenuatum are close wild kin, Hypericum perforatum itself is thought to be of hybrid origin, and ornamental garden species such as Hypericum patulum and Hypericum prolificum are cultivated for their showy flowers rather than for medicine. Only common St. John's Wort carries the standardized active-compound profile used in herbal supplements.

Where St. John's Wort grows

St. John's Wort is native to Europe and parts of temperate Asia, including Siberia, and has spread widely as a naturalised plant across North America, Australia and beyond. It favours open, sunny, well-drained ground — meadows, woodland clearings, roadsides, field margins and shelterbelts. Its tolerance of poor soils and disturbed land explains both its abundance in the wild and its status as a problem weed in grazing regions.

Origin of the name St. John's Wort

The plant's Russian "hunter's" name, zveroboy ("beast-slayer"), comes from the harm it can cause grazing animals: livestock that eat it can develop swellings on the ears and around the mouth and eyes that often turn into painfully raw sores. Distressed animals injure themselves further — biting, striking against trees and the ground — and in severe cases the reaction proves fatal. This is the same photosensitising effect that, in milder form, makes the herb a concern for human users.

In English the name St. John's Wort points to a different tradition: the plant typically flowers around 24 June, the St. John's Feast marking the birth of John the Baptist, and was gathered then for protective and medicinal use. "Wort" is simply an old word for a herb or plant.

Common and Latin names

The botanical name is Hypericum perforatum, while common names include St. John's Wort, common St. John's Wort and perforate St. John's Wort. Using the Latin name matters when buying supplements, because only products standardised to Hypericum perforatum carry the active chemistry described below — ornamental Hypericum species are not medicinal substitutes.

Chemical composition of St. John's Wort

St. John's Wort owes its activity to a complex mix of phytochemicals, the two most studied being hypericin and hyperforin. Alongside these the herb contains pseudohypericin, flavonoids, tannins and essential oils, and it is this combination — rather than any single molecule — that produces its biological effects.

Active compounds and their properties

• Hyperforin — the compound most associated with the herb's effect on mood, and the one thought to drive both its antidepressant action and many of its drug interactions. Hyperforin also shows antibiotic properties in laboratory studies, including activity against bacteria such as Staphylococcus.
• Hypericin and pseudohypericin — red-pigmented compounds that contribute to the plant's biological activity and are largely responsible for photosensitivity, the heightened skin reaction to sunlight seen in both animals and humans.
• Flavonoids and tannins — supporting compounds linked to the herb's traditional astringent, anti-inflammatory and wound-healing uses.

Because the concentration of these compounds varies between products, dosage and standardisation are an ongoing problem with herbal preparations, a point returned to in the regulation section below.

Medicinal properties of St. John's Wort

The healing properties of St. John's Wort have been valued since ancient times, with traditional, topical and modern medicinal uses all documented. In folk medicine the herb has been used internally and applied externally; in scientific practice, preparations made from it have served as a wound-healing agent.

St. John's Wort preparations are applied as a wound-healing remedy for burns, boils (furunculosis) and carbuncles, for treating ulcers, and as a means of relieving spasm of the blood vessels and improving the blood supply to internal organs. These topical and skin applications remain among its better-supported traditional uses.

Folk medicine and homeopathy still make wide use of this remarkable medicinal plant, and scientific medicine has not overlooked it either. Water-based infusions of St. John's Wort are also used in veterinary practice to treat certain conditions in domestic animals.

History of St. John's Wort use

In Rus' the plant was called the "herb for 99 ailments" and was used to treat migraine, lung complaints and hypertension, as well as disorders of the respiratory tract and internal organs, mastitis, cough and haemorrhoids. Across medieval Europe it was a staple of herbal medicine, valued for wounds and nervous complaints, and Native American peoples likewise used Hypericum for skin conditions and other ailments — a broad folkloric record that spans continents and centuries.

How St. John's Wort works

St. John's Wort is thought to influence mood by raising levels of certain neurotransmitters in the brain, in particular serotonin, much as conventional antidepressants do. Hyperforin appears to reduce the reuptake of serotonin and other messengers, leaving more of them active between nerve cells. This serotonergic action explains both why the herb may help mild depression and why combining it with other serotonin-affecting drugs is risky.

St. John's Wort as an antidepressant

St. John's Wort is the herbal remedy most often taken for low mood, and it is the comparison with pharmaceutical antidepressants that drives most modern interest in the plant. The sections below summarise current applications, the clinical evidence, and how the herb measures up against prescription drugs.

Use for depression: the modern view

Today St. John's Wort is used mainly for mild to moderate depression, usually taken as a standardised extract in capsule, tablet, tincture or tea form. Some people also try it for menopause symptoms and other mood-related complaints. The U.S. National Center for Complementary and Integrative Health (NCCIH), part of the National Institutes of Health (NIH), notes that evidence for these uses is mixed and that the herb is not a substitute for professional treatment of serious depression.

Clinical evidence and the research base

The strongest support for St. John's Wort comes from systematic reviews of mild-to-moderate depression. A widely cited Cochrane review of trials catalogued in databases such as PubMed concluded that St. John's Wort extracts were more effective than placebo and broadly comparable to standard antidepressants for milder depression, while producing fewer side effects in the studied trials. Reviewers also stressed that results varied with the product used and that findings may not extend to severe depression — one reason healthcare providers remain cautious.

Comparison of St. John's Wort with prescription antidepressants

Compared with prescription antidepressants such as SSRIs (selective serotonin reuptake inhibitors), St. John's Wort often shows a gentler side-effect profile in trials but carries a major drawback: it interacts with a wide range of medications and is not regulated to the same standard. Prescription antidepressants are tested and approved by the FDA, with defined dosing and quality control, whereas St. John's Wort products vary in strength from bottle to bottle.

Comparison with fluoxetine (Prozac) and placebo

Head-to-head trials have compared St. John's Wort with fluoxetine, sold as Prozac, a common SSRI. In several studies of mild-to-moderate depression the herb performed similarly to fluoxetine and better than placebo, with some trials reporting fewer adverse effects for the herbal extract. Even so, the herb's unpredictable potency and its drug interactions mean clinicians generally favour a properly dosed, monitored prescription where antidepressant treatment is genuinely needed.

Contraindications and precautions

St. John's Wort is not suitable for everyone, and several groups should avoid it or use it only under medical supervision. The herb's effect on the cytochrome P450 enzyme system and on serotonin makes it inappropriate for anyone taking interacting medication, and its photosensitising compounds raise the risk of sunburn.

Use during pregnancy and breastfeeding

St. John's Wort is generally not recommended during pregnancy or breastfeeding, because there is too little reliable safety data to consider it safe for the fetus or nursing infant. Authorities including the Mayo Clinic advise pregnant and breastfeeding women to avoid the herb unless a doctor specifically approves it.

Contraindications for specific groups

• People taking antidepressants — SSRIs, MAO inhibitors (monoamine oxidase inhibitors, MAOIs) or other serotonergic drugs — because of serotonin syndrome risk.
• Organ transplant recipients on cyclosporine, where the herb can dangerously lower drug levels.
• People living with HIV taking certain antiretrovirals, whose effectiveness the herb can reduce.
• Anyone on blood thinners, heart medication such as digoxin, or who relies on hormonal birth control.
• Fair-skinned individuals and those with a lot of sun exposure, who are more prone to photosensitivity reactions.

Side effects and adverse reactions

St. John's Wort can cause side effects even when taken alone, and adverse reaction reports include photosensitivity, digestive upset, fatigue, restlessness, headache, dry mouth and dizziness. Photosensitivity — increased skin sensitivity to sunlight, the mild human echo of the severe reaction seen in grazing animals — is among the most characteristic, so users are advised to limit strong sun exposure. Concerns about weight gain and long-term safety are less well established but are sometimes raised, which is another reason the herb is best used under guidance.

Risk of serotonin syndrome

The most serious risk of St. John's Wort is serotonin syndrome, a potentially dangerous build-up of serotonin that can occur when the herb is combined with other serotonin-raising drugs such as SSRIs or MAOIs. Symptoms range from agitation, rapid heartbeat, high blood pressure and sweating to confusion, muscle rigidity and, in severe cases, life-threatening complications. Anyone already taking an antidepressant should not add St. John's Wort without medical advice.

Drug interactions

St. John's Wort interacts with an unusually broad range of medications, which is the single biggest reason healthcare providers hesitate to recommend it. The Cleveland Clinic and other medical references list interactions spanning antidepressants, blood thinners, heart drugs, HIV medicines, pain medications, contraceptives and sedatives such as benzodiazepines, including Xanax. Pharmacists such as Blair Green Thielemier and Jeremy Wolf, and horticulture writers including Gerald Klingaman of the University of Arkansas System Division of Agriculture, have all highlighted that "natural" does not mean free of pharmacological risk.

Effect on the cytochrome P450 system and drug metabolism

St. John's Wort induces enzymes in the cytochrome P450 (cytochrome 450) pathway, speeding up how the liver breaks down many drugs and so lowering their concentration in the blood. This enzyme induction can render medications less effective — sometimes dangerously so, as with cyclosporine in transplant patients or antiretrovirals in HIV treatment — and is the mechanism behind much of the herb's interaction profile.

Interaction with anticoagulants (blood thinners)

St. John's Wort can weaken the effect of blood thinners such as warfarin by accelerating their metabolism, reducing the drug's anticoagulant effect and raising the risk of clotting. The same enzyme-induction mechanism can also alter levels of heart medication like digoxin, so people on these drugs should not take the herb without close monitoring.

Effect on the reliability of contraceptives

St. John's Wort can reduce the effectiveness of hormonal birth control by speeding up the breakdown of contraceptive hormones, which has been linked to breakthrough bleeding and unintended pregnancy. Anyone relying on the pill or similar methods should treat this as a meaningful risk and seek advice before using the herb.

Regulation and product variability

St. John's Wort is sold as a dietary supplement rather than an approved drug, which means it is not assessed by the FDA (the U.S. Food and Drug Administration) in the way prescription antidepressants are. Under federal rules for herbal products and dietary supplements, the FDA does not approve these products before sale, and the manufacturer — not a regulator — is responsible for safety and for the accuracy of label claims. In the European Union and elsewhere, rules differ but variability remains. The practical result is that the amount of hyperforin and hypericin can differ widely between brands and even between batches, making consistent dosing difficult and reinforcing why standardisation is a known weakness of herbal medicine.

Harvesting and gathering St. John's Wort

St. John's Wort is harvested during flowering, from June through August, by cutting the upper parts of the stems together with the leaves, flowers, buds and unripe fruit. This is when the active compounds are most concentrated in the plant.

Unfortunately, mass collection of this healing herb can lead to its complete disappearance from an area. Numerous amateur gardeners and owners of garden plots can help conserve and increase stocks of St. John's Wort by growing it themselves.

Growing St. John's Wort in the garden

Cultivating St. John's Wort is straightforward. Dried seeds are sown in late autumn, without covering them, into soil that has been dug over and enriched with fertiliser beforehand. The plant tolerates poor ground and full sun, and once established it returns year after year from its crown.

Timing of the medicinal harvest

The collection dates for common St. John's Wort are given in the calendar for gathering medicinal plants, which helps growers cut the herb at the point of peak potency during its summer flowering.