St Johns Wort

St Johns Wort

St Johns Wort


St. John's Wort is a herb with the botanical name of Hypericum perforatum.


St. John's wort was named after St John's Day which falls on June 24, the approximate flowering season in the northern hemisphere. The plant is seen growing wild beside roadsides and hedges in Britain, Europe and Asia. It reaches up to a metre in height and has pale green leaves with black dots on the lower surface. The flowers are bright yellow with five petals. The whole plant above the ground is harvested when the plant is just flowering. The herb has a bitter astringent taste and an aromatic odour.
This herb contains many chemicals including a red pigment known as hypericin, as well as flavonoids, phenols, tannins and volatile oil.


Herbal supplements can alter the effects of certain drugs, including prescription medications. Always tell your Doctor about any prescription medications, non-prescription medications, herbs or other dietary supplements you are taking.

- St. John's Wort can increase the rate of breakdown of a large number of prescription medications by changing the substances (enzymes and transporters) that metabolise drugs. Contact your Doctor immediately if you experience any changes in the effects of your medications.

- St. John's Wort should not be used by people taking any of the SSRI's (selective serotonin re-uptake inhibitors), which are used for the treatment of anxiety and mood disorders such as depression. There have been reports of interactions between St. John's Wort and paroxetine, trazodone, sertraline as well as the serotonin-receptor blocker nefazodone (another anti-depressant drug). Combining any of these drugs has produced symptoms of serotonin excess (serotonin syndrome), which can cause euphoria, drowsiness, sustained rapid eye movement, overreaction of the reflexes, clumsiness, restlessness, feeling drunk and dizzy, muscle contraction and relaxation in the jaw, sweating, intoxication, muscle twitching, rigidity, high body temperature, mental status changes (including confusion and hypomania - a "happy drunk" state), shivering, diarrhoea, loss of consciousness and death. St. John's Wort may decrease the effects of the tricyclic antidepressant drugs amitriptyline and nortriptyline .

- St. John's Wort should not be used with digoxin (for the treatment of heart failure), as this herb reduces the effectiveness of digoxin in the body.

- St. John's Wort should not be used by people taking warfarin (an anticoagulant medication), as it may decrease the blood levels of this drug, thus reducing its medical effects in the body.

- St. John's Wort may interact with monoamine oxidase inhibitor drugs, which are used for depression, as this herb may act in a similar manner in the body to these antidepressant medications.

- St. John's Wort should not be used by people taking benzodiazepine drugs (e.g. nitrazepam), which are prescribed for insomnia, anxiety and panic attacks This herb may act in a similar manner to these drugs within the brain

- St. John's Wort should not be used with theophylline (a drug that is prescribed for asthma and other lung conditions such as emphysema and chronic bronchitis) as it may reduce the beneficial effects of this drug.

- St. John's Wort can interact with the oral contraceptive pill by increasing its rate of breakdown, thus causing breakthrough bleeding.

- St. John's Wort can also reduce the blood levels of cyclosporin (a drug that reduces the activity of the immune system and is prescribed for autoimmune diseases such as rheumatoid arthritis, severe psoriasis and to prevent organ transplant rejection) and indinavir (an anti-viral drug), thus reducing the beneficial effects of these drugs.

- St. John's Wort may reduce the effects of the antihistamine drug fexofenadine .

- St. John's Wort may decrease the effects of the anti-viral drug nevirapine .

- St. John's Wort may decrease the effects of the calcium channel blocker nifedipine, used to treat hypertension and angina. People

- St. John's Wort can interact with anaesthetics used when people have surgery. People who are taking St. John's Wort and who are going to have surgery should tell their Doctor well before surgery, as they will need to discontinue use of St. John's Wort some days before surgery.

- St. John's Wort may reduce the effects of the cholesterol-lowering drug simvastatin .

Medical use

Always consult your Health Professional to advise you on dosages and any possible medical interactions.
St John's Wort has been used traditionally for its effects on the nervous system. The herb has a mild sedative and restorative effect on the nervous system and may be useful in cases of anxiety, irritability, neuralgia, nerve damage or injury, nervous tension and general nervous debility.

St John's Wort has been found to be beneficial in the health management of mild depression. It may improve mental capacity, sleep quality and headaches in some people who suffer from depression. The herb is prescribed four times as often as fluoxetine in Germany.

Hypericin is an inactivator of infectious viruses in blood and may be useful in the management of some viral infections such as herpes, cold sores, some types of colds, and perhaps Hepatitis C. St John's Wort may also possess antibacterial properties. Antibacterial substances with resistance to, and activity against, strains of bacteria such as Staphylococcus aureus, have been found in St John's Wort.

St John's Wort has an anti-inflammatory action and helps to stimulate the growth and repair of skin tissue. St John's Wort oil or ointment has a long history of traditional use in the treatment of wounds and painful skin conditions such as bruises and shingles. For more information, see the St John's Wort (External Use) topic.


Antidepressant and sedative, antiviral, antibacterial, anti-inflammatory, wound healing and astringent.


- The effects of St. John's Wort have not been well studied, so its safety for the developing child has not been established. For this reason, it is recommended that women who are pregnant or breastfeeding avoid the use of St. John's Wort.
- It is extremely important to tell your Doctor and Pharmacist if you are taking St John's Wort.
- In rare cases, St John's Wort has caused increased nerve sensitivity, including tingling sensations and increased sensitivity to heat and cold.
- Possible side effects of St John's Wort include stomach upset, allergic reactions, confusion, dizziness, tiredness, dry mouth and photosensitivity.
- In Ireland, products containing St. John's Wort are only available on medical prescription.