St. John's wort: effects, side effects and interactions

St. John's wort (Hypericum perforatum) is one of Europe's best-known herbs, and it grows wild along Dutch roadsides. You can make tea from it, use it as an extract or grow it yourself from seed. In this guide you'll learn how to recognise the real thing, which form suits you, how to make tea, how to grow and harvest the plant, and what to watch out for if you take medication.

What is St. John's wort?

St. John's wort is a hardy perennial from the Hypericaceae family. It grows 30 to 100 centimetres tall and loves sunny, dry spots: roadsides, dykes, railway verges and wasteland. From June onwards it's covered in yellow flowers with five petals and a tuft of long stamens.

The name refers to St. John's Day on 24 June, when the plant is in full bloom. The second part of its Latin name, perforatum (perforated), points to the translucent dots in the leaves. Hold a leaf up to the light and it looks as if it's full of tiny holes. Those are oil glands.

How to recognise the real thing

Gardens and parks often have other Hypericum species, and roadsides are full of other yellow flowers. Look for these features:

• Translucent dots in the leaf when you hold it up to the light.
• Two raised lines running along the round stem.
• Flowers of 2 to 3 cm with tiny black dots along the edges of the petals.
• Red fingers: crush a flower bud and your skin turns purplish red, thanks to a compound called hypericin.

Large-flowered garden St. John's wort (Hypericum calycinum) has flowers of 5 cm or more and grows as a low ground cover. That's not the species this guide is about.

What's in it and how does it work?

St. John's wort contains dozens of compounds. The main ones are hyperforin, the red pigments hypericin and pseudohypericin, and flavonoids such as hyperoside and rutin. How much of each a product contains depends on where the plant grew, when it was harvested and how it was extracted.

The best researched effect takes place in your liver. Through the pregnane X receptor (PXR), hyperforin ramps up production of the enzyme CYP3A4. That enzyme breaks down more than half of all medicines. More CYP3A4 means your body clears those medicines faster. That's why it matters what else you're taking, more on that further down. St. John's wort is mainly known as a traditional herbal tea. No health claims have been approved for the herb in the EU, so we don't promise any effects either.

Tea, extract or seeds: which form should you choose?

At Dutch-Smart you'll find St. John's wort in four forms. Here's how they differ:

	Dried herb	1:1 extract	20% extract	Seeds
Contents	50 grams	10 ml	10 ml	1 gram
Form	Cut flowering herb	Liquid herbal extract	Liquid extract in an ethanol and water base	Thousands of tiny seeds
Strength	Mild	Stronger than tea	Highly concentrated	n/a
Use	Tea, 1 to 2 teaspoons per cup	Drops, as directed on the packaging	Start with 5 to 10 drops, diluted in water	Sow in spring
Best for	Anyone who wants a traditional herbal tea	Anyone who'd rather not brew tea	Experienced users who want a small dose	Gardeners and anyone who wants to harvest their own

New to it? Start with the 50 grams of dried St. John's wort. Tea is the mildest form and you decide how strong you make it. Don't feel like brewing? The St. John's wort 1:1 extract from our tinctures is a practical alternative. The St. John's wort 20% extract is much stronger per drop. Build up slowly and read the safety table below carefully.

Making St. John's wort tea in 5 steps

1. Put 1 to 2 teaspoons of dried St. John's wort in a tea strainer or teapot.
2. Pour a cup of boiling water over it, about 250 ml.
3. Cover the cup or pot and let it steep for 10 to 15 minutes. A lid keeps the fragrant oils in your tea.
4. Strain out the herb. The taste is herbal and slightly bitter. A teaspoon of honey or a slice of lemon softens it.
5. Stick to a maximum of three cups a day.

Store the herb in an airtight jar, somewhere dry and dark. In the light it quickly loses colour and aroma. You'll find more herbs to brew in our tea category.

Growing St. John's wort from seed

St. John's wort is a rewarding plant to grow yourself. It's hardy, isn't fussy about soil and comes back every year. With the St. John's wort seeds (1 gram) you'll have more than enough for a decent border. The only thing to keep in mind: the seed needs light to germinate and prefers cool conditions.

Sowing

1. For better germination, put the seeds in the fridge for 3 to 4 weeks first, in a bag with a little damp sand. If you sow directly outdoors in early spring, nature does this for you.
2. Fill a seed tray with seed or cutting compost, press it down lightly and water it.
3. Scatter the seeds thinly over the surface and press them in. Don't cover them with soil, they need light to germinate.
4. Put the tray somewhere bright, but out of harsh midday sun, with a clear lid or plastic over it. The ideal temperature is around 15 °C. Above 20 °C the seed germinates less well.
5. Keep the soil moist with a spray bottle. After about two to three weeks you'll see the first seedlings.

Planting out and care

Once the seedlings have four to six leaves, prick them out into individual pots. After the last night frost, usually mid-May, plant them in the garden about 30 centimetres apart. Choose the sunniest spot you have. Any well-drained soil will do and feeding isn't necessary. Once established, the plant copes well with drought. In the first year it mainly grows leaves, flowering usually starts in the second year. St. John's wort self-seeds readily. If you don't want that, cut off the spent flower heads before the seed capsules turn brown.

Harvesting and drying

1. Harvest from the second year, in June or July, when about half the flowers are open and the rest are still in bud.
2. Pick in the morning, once the dew has dried.
3. Cut off the top 20 centimetres of the flowering stems.
4. Tie them in small bunches and hang them upside down somewhere dark and airy. A food dehydrator works too, at 30 to 40 °C.
5. Once the herb rustles dry, strip the flowers and leaves from the stems and store them in a dark glass jar.

You'll find more seeds for your herb garden in growing seeds. Fancy a growing project with water? Read how to grow blue lotus from seed.

Safety: what you need to know

St. John's wort is a potent herb. Because it speeds up the breakdown of many medicines, these are the combinations to watch out for:

Combination	What happens	Advice
The pill and other hormonal contraception (patch, ring, implant)	The hormones are broken down faster, so your protection against pregnancy can drop.	Don't combine. After stopping, use an extra method for another 4 weeks, such as condoms.
Antidepressants (SSRIs)	Risk of too much serotonin, with restlessness, sweating, fever and muscle twitching (serotonin syndrome).	Don't combine.
MAO inhibitors (such as ayahuasca) and MDMA	The same risk of too much serotonin.	Don't combine.
Blood thinners	They can work less well, and become stronger again once you stop the St. John's wort.	Talk to your doctor or anticoagulation clinic first.
Sun and sunbeds	Hypericin makes your skin more sensitive to UV light, so you burn faster.	Avoid strong sunlight, also when you use St. John's wort oil on your skin.

Other known side effects are stomach and bowel complaints, dizziness and restlessness. Don't use St. John's wort if you're pregnant, breastfeeding or under 18, and stop at least ten days to two weeks before planned surgery. Taking other medicines? Check with your pharmacist whether the combination is safe. You'll find the full list of interactions at your pharmacy and in the RIVM risk assessment (see the sources below).

Common mistakes

• Covering the seeds with soil: St. John's wort needs light to germinate. Under a layer of soil it barely sprouts.
• Sowing too warm: on a warm windowsill above a radiator the seed germinates poorly. Around 15 °C works best.
• Picking the wrong plant: ragwort also grows on roadsides, with yellow flowers in flat clusters and no translucent dots in the leaves. That plant is poisonous. Only pick what you're sure of.
• Steeping uncovered or too briefly: you end up with a weak cup. Give it 10 to 15 minutes with a lid on.
• Storing the dried herb in the light: it loses colour and aroma. Use a dark, airtight jar.
• Assuming the effect is gone straight away: the effect on your liver lasts another one to two weeks after you stop.

Frequently asked questions

How long should St. John's wort tea steep?

Let it steep for 10 to 15 minutes, with a lid on the cup or pot. Use 1 to 2 teaspoons of dried herb per cup of about 250 ml.

Does St. John's wort flower in its first year from seed?

Usually not. In the first year the plant mainly builds roots and leaves. From the second year it flowers every summer, starting in June.

Is St. John's wort legal in the Netherlands?

Yes. St. John's wort is freely available as a herb, extract and seed, and falls under the Dutch Commodities Act (Warenwet). The Dutch government has decided to make a warning about interactions with medicines mandatory on products containing St. John's wort.

Can I use St. John's wort while on the pill?

No, that's not recommended. St. John's wort can make the pill less reliable, even weeks after you've stopped. If you still want to use St. John's wort, talk to your GP about another form of contraception.

How long does St. John's wort stay in your body?

The compounds themselves leave your blood within a few days. The effect on your liver enzymes lasts one to two weeks. For hormonal contraception a wider margin of four weeks is used.

Where can I buy St. John's wort?

You'll find dried St. John's wort and more herbs among our relaxing herbs. The 1:1 extract is in tinctures, the 20% extract in liquid alkaloid extracts and the seeds in growing seeds.

Sources: RIVM, Risk assessment of herbal preparations containing St. John's wort (2021), Lareb, Mandatory warning for St. John's wort, Moore et al., PNAS 2000 (hyperforin and PXR), OMAFRA, St. John's wort growing guide.