St. John's Wort

Hold a leaf to the light and it is full of translucent pinholes; crush a flower bud and your fingers stain red. That plant is the biggest drug-interaction problem in herbal medicine - it makes the body clear contraceptives, blood thinners, transplant and HIV drugs faster - and a listed noxious weed across much of the West.

Recognition and movement rather than planting: paired stalkless leaves full of translucent dots, a two-ridged stem, yellow flowers with black-dotted petal edges and red-staining buds - spreading by short crown runners and by sticky seed that rides on boots, tires, hooves and hay and stays viable for a decade.

You are not going to plant this, so what matters is knowing it and knowing how it moves.

The plant. An upright perennial, usually 1 to 3 feet, growing in a tight clump from a woody crown. The stems are wiry, often reddish, and carry two raised ridges running down opposite sides — roll one between your fingers and you can feel that it is not round. Leaves are small, oval, stalkless, and set in opposite pairs, and every one of them is dotted with translucent oil glands that show as pinpricks against the light. There are usually black dots along the leaf and petal margins too.

The flowers are the showy part: flat-topped clusters of bright yellow five-petalled blooms about three-quarters of an inch across, each with a spray of long stamens, opening from June into August. Crushed buds stain purple-red. Small three-parted capsules follow and dry rusty brown, and the plant reddens as it goes over.

How it spreads is both ends at once. Below ground the woody crown pushes out short lateral runners that send up new shoots a few inches away, so a single plant thickens into a patch and any crown or runner fragment left in the ground regrows. Above ground a mature plant sets thousands of tiny seeds, sticky when wet, that travel on boot treads, tires, mower decks, hooves, dog coats, hay and moving soil — and then wait, staying viable in the seed bank for ten years or more. That combination is why one clean-looking season means nothing.

Lookalikes. The important distinction is with the garden hypericums. Shrubby St John's wort (Hypericum prolificum) is a well-behaved native eastern shrub, and the popular landscape selections like 'Hidcote' and H. x moserianum are woody, clump-forming and not invasive; all of them are shrubs with larger flowers, and none has the wiry two-ridged herbaceous stem of H. perforatum. Hypericum calycinum, sold as Aaron's beard or creeping St John's wort, is a different problem — a low evergreen groundcover that spreads hard by rhizome and is best kept out of a small garden for that reason alone. Among the native herbaceous hypericums, the tell remains the same: pinhole oil glands on the leaves, ridged stem, red-staining bud.

Control, not care. Cut at full bloom so it cannot seed, dig small clumps out whole including the crown and runners, and expect to keep checking the ground for years because the seed bank outlives the plants. Grazing sheep on it is the one thing never to do.

Everything here is control. The plant has two engines — a woody crown that runs sideways and a seed bank that lasts a decade — and a method has to answer both.

Cutting is the cheapest useful action. A stand cut at full bloom sheds no seed that year. It will regrow from the crown, so this is containment rather than a cure, but it stops the problem getting bigger while you plan. Cutting after the capsules brown does nothing except scatter them.

Digging works on a new plant or a small clump. Moist soil, a fork rather than a spade, lift the whole woody crown and follow the short runners out sideways — a crown fragment or a runner bud left behind simply resprouts. Then keep the appointment: check every two or three weeks through the season and pull each resprout, because it is the repeated removal that empties the crown. Do not rototill a patch, and do not compost what you pull.

Herbicide is what large infestations actually get treated with, and timing decides the result: systemic products work on actively growing plants from bud to early bloom, and again on autumn regrowth, when reserves are moving down into the crown. Use a product whose label lists the site you are treating — pasture, rangeland, non-crop area, ornamental bed — and follow that label, which is legally binding. Pasture products often carry grazing and haying restrictions. Expect several years of follow-up.

Biological control is the one genuinely famous success story here. The leaf beetles Chrysolina quadrigemina and C. hyperici, released in northern California in the 1940s, collapsed Klamath weed across millions of acres and are now established through much of the West; in many places they hold the plant at a fraction of its former abundance without anyone doing anything. If your stand is being skeletonised by small metallic beetles, that is what is happening, and it is worth leaving alone.

Then close the ground. St. John's wort colonises bare, disturbed, overgrazed ground and struggles against dense established vegetation. Reseeding a cleared area with competitive grasses and managing grazing so the sward stays thick does more long-term work than any single treatment. And clean your boots, tires and mower before you leave an infested area — that is how it makes the jumps no amount of digging can undo.

The most-studied herb in the world and the biggest drug-interaction problem in herbal medicine at the same time. It induces CYP3A4 and P-glycoprotein, cutting the effect of contraceptives, anticoagulants, transplant drugs and HIV antiretrovirals, and it can push serotonergic drugs into serotonin syndrome. Educational information, not medical advice.

This section records how people have traditionally used this plant, and what is known about the risks. It is history and general information — not medical advice, and not a recommendation to treat anything. Plants are not dosed like medicines, some interact with prescriptions, and some are harmful in ways that are not obvious. Talk to a clinician before using any plant medicinally.

Two things about St. John's wort are true at once, and the second is the reason this page exists.

What the research actually shows. Standardised extracts of the flowering tops have been through dozens of randomised trials for depression — more than any other herbal preparation has ever received. Systematic reviews of that work have generally found them better than placebo and broadly comparable to standard antidepressants for mild to moderate depression, with fewer reported side effects; in Germany it has been a licensed medicine for decades. The picture is much weaker for severe depression, trial quality and extract strength vary a great deal, and in the United States the product is sold as an unregulated supplement, so what is in the bottle varies between brands and between batches. None of that is a recommendation. Depression is something to take to a clinician, and this is a plant with consequences.

The interactions are the headline. St. John's wort switches on the liver enzyme CYP3A4 and the drug transporter P-glycoprotein. Between them, those two handle a large share of all prescription medicines, and turning them up means the body clears those medicines faster than the dose assumes. The drug does not become dangerous; it stops working. The documented consequences include failed oral contraceptives, with breakthrough bleeding and unplanned pregnancies; loss of control on warfarin and other anticoagulants; organ rejection in transplant patients taking ciclosporin or tacrolimus; loss of viral suppression on HIV antiretrovirals, which risks resistance; and reduced levels of digoxin, some statins, some cancer drugs, and many others. The effect builds over one to two weeks and takes a similar time to wear off after stopping, so stopping it abruptly can send drug levels the other way.

The other interaction is serotonergic. Combined with SSRIs, SNRIs, triptans, tramadol or other serotonergic drugs, St. John's wort can contribute to serotonin syndrome — agitation, sweating, tremor, fast heartbeat, and in serious cases a medical emergency. Never add it on top of a prescribed antidepressant, and never swap one for the other without your prescriber managing the change.

Its own side effects are mostly mild — stomach upset, restlessness, sleep disturbance — with one exception worth knowing: photosensitivity. Hypericin makes skin more reactive to sunlight, and while serious cases in people are uncommon at ordinary doses, fair-skinned users on higher doses do burn more easily. In grazing animals the same compound causes severe, sometimes fatal photosensitisation, which is covered under this plant's threats.

The practical rule is short: tell your prescriber and your pharmacist before you take St. John's wort and before you stop it, and treat it as a drug rather than as a harmless tea. This is educational information, not medical advice.

Named for St John's Day and hung over doorways against evil for a thousand years, gathered for the blood-red oil, then shipped to America - where it became Klamath weed, took millions of acres of western range, and was beaten back by imported leaf beetles in one of the great biological-control successes.

The name is medieval and literal. The plant blooms around 24 June, St John's Day, and the red juice from its crushed buds was read as the blood of John the Baptist; wort is simply the Old English word for a useful plant. It was gathered at midsummer, hung over doors and windows to turn away evil, and steeped in oil to make the deep red infused oil still sold today for bruises and burns. Classical writers knew it, medieval herbals list it, and it carried a reputation for lifting melancholy long before anyone could say why.

It came to North America with European settlers, and in the West it turned into something else entirely. Around Klamath County, Oregon and the northern California ranges it escaped into overgrazed, logged and disturbed country and became Klamath weed, spreading across millions of acres of rangeland by the 1940s, driving down grazing capacity and land values and blistering the livestock that ate it. The response became a landmark: entomologists imported the European leaf beetles Chrysolina quadrigemina and C. hyperici, released them in northern California in 1945-46, and watched the infestation collapse. It was the first great biological control success against a weed in North America, and it is why a plant that once dominated whole valleys now persists there as scattered patches. A monument to the beetle stands in Humboldt County.

The modern chapter is pharmaceutical. German research from the 1980s onward standardised extracts of the flowering tops and put them through clinical trials, and by the 1990s St. John's wort had become one of the best-selling supplements in the world. Then, in 2000, published reports of transplant patients rejecting organs and of HIV drug levels collapsing revealed the enzyme induction behind it, and regulators worldwide issued warnings. In a single decade the plant went from folk remedy to blockbuster supplement to the standard textbook example of a herb-drug interaction — which is, in the end, the most useful thing a gardener can know about it.

How to be sure it is this plant and not a garden hypericum, why a cleared patch keeps coming back, what the white sunburn on your pale-faced sheep means, whether the beetles eating it are a problem, and what to do if you are taking it and about to start a prescription.

“Is this it, or a garden St John's wort?” Check the stem and the leaf. Hypericum perforatum is herbaceous, with a wiry two-ridged stem and small paired leaves peppered with translucent pinhole dots. The landscape plants — 'Hidcote', H. x moserianum, the native shrubby H. prolificum — are woody shrubs with bigger flowers and no ridged herbaceous stem. When in doubt, crush a bud: the red stain is the giveaway.

“I cleared it and it came back.” Expected, from either engine. Either a piece of the woody crown or a runner bud stayed in the ground, or the seed bank germinated — and that seed stays viable for ten years or more. Plan on several seasons of checking the same ground rather than a single push.

“My sheep have blistered, peeling faces.” That is classic photosensitisation, and it happens on unpigmented skin: white faces, pink noses, bare ears and udders. Get the animals off the stand and out of direct sun, and call a vet — severe cases are painful and can be fatal. Pale-skinned animals are at the highest risk, and hay cut from an infested field carries the problem indoors.

“Small metallic beetles are eating it.” Leave them. Those are almost certainly the imported Chrysolina biocontrol beetles, and they are the reason the West is not still buried in this plant. Do not spray a stand that beetles are working on.

“I take it, and my doctor just prescribed something.” Say so, before the first dose, and say so again if you plan to stop taking it — the enzyme effect takes one to two weeks to build and a similar time to fade, so both starting and stopping shift your drug levels. The same goes for the pharmacist. If you are on a contraceptive, an anticoagulant, a transplant drug, an HIV medication or an antidepressant, treat this as urgent rather than routine.

“Can I just make the red oil from what is growing here?” The tradition is real, and this catalog is still not going to walk you through it: the plant is a noxious weed you should be removing rather than cultivating, home preparations have no dose control, and the interactions are the same whatever form it is in. If you want the oil, buy it, and tell your prescriber you use it.

“Is it illegal to have?” It is not federally listed, but it is a state-listed noxious weed across much of the West — including California, Colorado, Idaho, Montana, Nevada, Oregon and Washington — where planting, selling or moving it is restricted and control may be required. Listings change; check your own state's current noxious weed list before assuming either way.

Hardy roughly zones 3 to 9 and recorded in nearly every state, but it dominates where summers are dry and the ground is disturbed or overgrazed: the Pacific Northwest, northern California, the northern Rockies and the northern Plains. Humid Southeast heat and dense competition hold it back.

St. John's wort is hardy over a very wide range — roughly zones 3 to 9 — and has been recorded in nearly every state and Canadian province. Where it becomes a problem is a narrower map, and it tracks disturbance and dry summers rather than cold.

Pacific Northwest, northern California and the northern Rockies: its American heartland, and the ground where it earned the name Klamath weed. Dry summers, logged and grazed country and abundant open disturbed soil suit it perfectly, and it is a listed noxious weed through most of this region. Biological control keeps many stands well below their historic peaks, but the plant is everywhere.

Northern Plains and Great Lakes: common on roadsides, old fields and pasture, locally dense on light soils and thin ground, and listed in several states.

Northeast and mid-Atlantic: widespread and familiar on roadsides and old pasture, but usually a component of the vegetation rather than a takeover — wetter summers and heavy competition from other perennials keep it in check.

Southeast: present, least aggressive. Hot humid summers, dense warm-season growth and heavy disease pressure hold it back, and it rarely dominates.

Arid Southwest: largely limited to irrigated ground, mountain meadows and higher elevations; it needs more moisture than open desert offers.

What favours it everywhere is bare, disturbed, overgrazed and light-textured ground with full sun. What limits it is shade, dense established vegetation and repeated cultivation. Winter is no help at all — the crown is hardy well past anything the temperate US produces.