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St. John’s wort (Hypericum perforatum L.) is a plant very common in the peninsula and acclimatized in numerous temperate zones around the world: China, America, Australia, Europe, North of Asia. It is located at the edge of arable lands, roadsides, ditches and edges of forests.



The generic name Hypericum derives from the Greek word “hyperikon”, which means something like everything above images, alluding to the property attributed to Hypericum perforatum of “scaring away evil spirits.”

It is a medium-sized plant with hairless and branched stems. It has triangular and opposit leaves, with rounded edges. These leaves, looking at them against the light, seem perforated, which gives them the name of their specific epithet: perforatum. Actually, they are not perforated but have a lot of oily glands in those areas.

It has a very characteristic flower, with five yellow petals and smaller sepals. The sepals are striped and covered with black glands.

St. John’s wort is the most consumed medicinal plant on the planet. It is sold in almost all drugstores and herbalists’ shops as a plant to prepare infusions with or, most frequently, in capsules, as an extract. The useful part is the flowery ends and its main medicinal use is to treat mild or moderate depressions. The “scaring evil spirits” comes probably from that.

Despite its extensive use around the planet, this plant should not be taken lightly, but rather must be consumed in a controlled and precise manner. The European Medicines Agency (EMA)’s monograph indicates a well-established medical use in the treatment of mild to moderate depressive episodes with this plant. Its efficacy is similar to conventional antidepressants.

The major constituents of St John’s wort include naphtodiantrones, hypericin, hyperforin, pseudohypericin, isohypericin and protohypericin; however, the substance responsible for the main medicinal activity has not been identified yet. The hyperforin present in St John’s wort has shown to result in cognitive enhancement, memory enhancement, neuroprotective effect, and inhibition of the reuptake of different neurotransmitters (serotonin, dopamine, and noradrenaline), which could explain the plant’s antidepressant activity.


Hypericum perforatum or St. John’s wort’s flower. It is a very characteristic flower.

One must be careful with St. John’s wort because it can cause photo sensitivity, ie reactions similar to sunburns in parts of the body exposed to intense sunlight, especially in people with white skin. Gastrointestinal disorders, allergic reactions (redness, itching and rash), tiredness, or restlessness may occur on rare occasions. The medicinal plant can interfere in numerous medications such as antivirals, antibiotics, blood coagulation inhibitors, sleep inducers, oral contraceptives… so one should consult a specialist before consuming it.

Another application of St. John’s wort is its oil. This oil is obtained by macerating the flowering tops in a bottle of olive oil, leaving it out in the sun for about 40 days, and afterwards filtering the oil and keeping it, if possible, in opaque bottles. This oil is used as an analgesic for muscle and joint pains, it also has antiseptic properties, so it is commonly used to treat wounds and burns.

After its use one should not sunbathe, as spots on the skin difficult to remove might appear. So a piece of advice is to use it only in winter or at night. Each time the bottle is opened, active substances react with the oxygen of the air and are lost, so it is convenient to collect it in several small containers and use one at a time.