St. John's wort: forms, use and interactions

Few native medicinal plants are as well known, and at the same time as underestimated, as St. John's wort. Its golden-yellow flowers greet us along every summer roadside, and the plant looks back on centuries of traditional use. But precisely because St. John's wort seems so familiar, one crucial point is often overlooked: it is among the plant substances with the most relevant interactions. In this guide, you'll learn what forms are available, what to pay attention to when using it, and why a conversation with a doctor or pharmacist before taking it is a good idea.

What is St. John's wort?

St. John's wort, botanically Hypericum perforatum, is a perennial herbaceous plant from the family Hypericaceae. It grows up to a metre tall and bears bright yellow flowers from June to August. Its English name comes from its flowering period around the feast of St. John the Baptist on 24 June. A characteristic identifying feature: if you hold the leaves up to the light, they appear to be perforated with tiny holes. These apparent "holes" are actually tiny glands filled with essential oil – hence the species name "perforatum" (perforated).

If you rub the yellow flowers between your fingers, a reddish juice is released. This so-called "blood of St. John" effect is due to the pigment hypericin, one of the plant's most important compounds. St. John's wort grows wild in Europe, North Africa and Western Asia and is now found worldwide. It has been used traditionally since antiquity; in modern phytotherapy, it is one of the most thoroughly researched medicinal plants of all.

For use as a medicinal herb, the flowering plant is harvested – usually the upper, flower-bearing shoot tips shortly before or at the start of flowering, when the content of valuable compounds is at its highest. It is then gently dried and processed further depending on its intended use. Origin, harvest timing and drying method largely determine the resulting quality, which is why reputable manufacturers place great importance on controlled cultivation and tested raw material.

The compounds: hypericin and hyperforin

St. John's wort contains a complex mixture of more than a dozen groups of active compounds. Two marker substances are central, serving as a reference point when standardising extracts:

• Hypericin (and pseudohypericin): the red pigment from the naphthodianthrone group. It's regarded as a marker substance and is used to standardise many preparations. Hypericin is also partly responsible for the increased skin sensitivity to light that can occur with very high intake.
• Hyperforin: a phloroglucinol derivative that is today considered particularly relevant for its activity in the nervous system. Hyperforin is also the substance chiefly responsible for interactions with medications.

Also present are flavonoids such as rutin, hyperoside and quercetin, tannins, and essential oils. It is only the interplay of these substances – the so-called multi-compound complex – that makes up the plant's characteristic profile. Content varies considerably depending on location, harvest timing and processing, which is why standardised extracts offer a clear quality advantage over loose herb.

Forms & extracts: tea, oil and standardised capsules

St. John's wort is available in very different forms, which vary considerably in content and application:

• St. John's wort tea: brewed from the dried herb. The mildest form, though with a strongly fluctuating and generally low content of active compounds – in particular, the fat-soluble hyperforin barely transfers into the infusion.
• Red oil (St. John's wort oil): an infusion of the flowers in vegetable oil, which gets its typical red colour from the hypericin. It is traditionally used externally to care for stressed skin.
• Standardised extracts: the most concentrated form. Here, the herb is extracted with alcohol or water and adjusted to a defined content of hypericin or hyperforin. Figures such as "10:1" mean that one part of extract was obtained from ten parts of starting material – so the extract is concentrated accordingly.

The advantage of standardised dry extracts lies in their consistent composition: a defined extract delivers a comparable content of marker substances from batch to batch. Anyone interested in a preparation should therefore look for clear information on extraction ratio and standardisation. As with other herbal guides – for example on black cumin oil or schisandra berry – the same principle applies: the form plays a role in determining both content and applicability.

Use & intake

How St. John's wort is used depends on the form chosen. For finished preparations and food supplements, follow the dosage recommendation on the packaging; this should not be exceeded on your own initiative. Standardised extracts are usually taken as capsules or tablets, often with a meal and plenty of liquid.

An important practical note concerns patience: herbal preparations generally don't take effect immediately, but only after a certain period of use. Stopping abruptly, as well as combining several products containing St. John's wort, should be avoided. For good tolerability, it has proven helpful to take the preparation regularly at the same time of day and not to keep interrupting use. If you're using other food supplements at the same time, keep an eye on their ingredients to avoid duplication. Because St. John's wort can increase the skin's sensitivity to light, caution is advisable for fair-skinned individuals and during intense sun exposure. For pregnant and breastfeeding women, as well as for children, use is only advisable following explicit consultation with a doctor.

Interactions: the most important point about St. John's wort

St. John's wort is a plant – but "plant-based" doesn't automatically mean "harmless". In fact, St. John's wort is among the substances with the most numerous and clinically significant drug interactions. The reason lies in its mechanism of action: hyperforin, above all, activates the body's own enzyme systems in the liver (including CYP3A4) as well as a transport protein called P-glycoprotein. These systems break down many medications. When St. John's wort is taken, they work faster – so other medications are broken down more quickly and lose effectiveness.

Among the groups of medications affected are:

• Hormonal contraceptives (the "pill"): St. John's wort can weaken the effect of contraceptives, so that contraceptive protection is no longer reliably guaranteed. Cases of breakthrough bleeding and unintended pregnancies have been documented.
• Blood thinners (anticoagulants): with active substances such as phenprocoumon or warfarin, blood levels can drop and the anticoagulant effect can diminish.
• Antidepressants: taking it at the same time as certain antidepressants (such as SSRIs) can lead to a dangerous excess of the messenger substance serotonin (serotonin syndrome).
• Other medications: including certain HIV and cancer medications, immunosuppressants used after transplants, heart medications such as digoxin, and some cholesterol-lowering drugs.

This list is not exhaustive. The clear recommendation is this: anyone who regularly takes medication should check with a doctor or pharmacist before taking St. John's wort. Stopping should also not be abrupt, and is ideally supervised, since the breakdown of other medications changes again afterwards. This is no reason to panic – but it is a good reason to proceed informed and with professional guidance.

Honestly assessed

St. John's wort is one of the most thoroughly researched medicinal plants and looks back on a long tradition of use. At the same time, it is not just any casual "feel-good herb": its profile of activity is real, and precisely for that reason its interactions need to be taken seriously. Anyone not on regular medication can use St. John's wort preparations within the recommended application; anyone taking medication should seek professional advice beforehand.

Unrealistic promises have no place here: St. John's wort is no substitute for medical treatment, and for persistent complaints, a doctor's advice is always the right place to turn. Understood as a food supplement, it complements a conscious lifestyle – it does not replace it. This honest assessment matters more to us than bold claims.

Matching products from Scheunengut

If you'd like to try St. John's wort, look for a well-thought-out formulation and transparent information. Our complex with St. John's wort, valerian, passionflower, folic acid and vitamin B12 combines traditionally valued plant compounds in capsule form. Vitamin B12 and folic acid contribute to normal function of the nervous system and normal psychological function. You'll find more plant-based topics in our guide section, for example on ginger or sage. Please always keep the interactions described above in mind with products containing St. John's wort, and when in doubt, consult a doctor or pharmacist.

Frequently asked questions (FAQ)

What interactions does St. John's wort have with medications?

St. John's wort activates enzymes in the liver and can thereby speed up the breakdown of many medications. Those affected include the contraceptive pill, blood thinners, certain antidepressants, and HIV, cancer and heart medications, among others. Anyone on long-term medication should check with a doctor or pharmacist before starting to use it.

Can St. John's wort affect the pill's effectiveness?

Yes. St. John's wort can weaken the effect of hormonal contraceptives, so that contraceptive protection is no longer reliable. Breakthrough bleeding and unintended pregnancies have been documented. Anyone using hormonal contraception should be sure to seek medical advice before taking St. John's wort.

What does the "10:1" figure mean for St. John's wort extracts?

The extraction ratio "10:1" indicates that one part of extract was obtained from ten parts by weight of dried herb. The extract is therefore concentrated. In addition, high-quality extracts are standardised to a defined content of marker substances such as hypericin or hyperforin, which ensures a consistent composition.

What's the difference between St. John's wort tea and extract?

Tea provides only a low and strongly fluctuating content of active compounds, since the fat-soluble hyperforin in particular barely transfers into the infusion. Standardised extracts, by contrast, contain a defined, concentrated proportion of marker substances and deliver comparable amounts from batch to batch – making them the more reliable form.

Does St. John's wort make the skin sensitive to light?

The pigment hypericin, in particular, can increase the skin's sensitivity to sunlight, especially with high intake and fair skin. It's sensible to avoid intense sunbathing and sunbed use while taking it, and to make sure you use adequate sun protection.