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St John's Wort: A Herb's Double-Edged Sword

St John's Wort: A Herb's Double-Edged Sword

Herbal supplements can have stronger side effects than most people believe. HealthAnswers checks out a notoriously potent herb that can interact with prescription drugs.

Chong Pei Lan

Historical Beginnings
St. John's Wort (Hypericum perforatum) is a herbaceous perennial with bright yellow cluster flowers that secrete a red liquid when pinched. The plant was named by the early Christians in honour of St. John the Baptist. The red oil glands that dot the herb's leaves were once believed to be drops of blood, a reminder of the day the saint was beheaded. It is now known that the oil glands contain the red pigment hypericin and is regarded as the key constituent even though there are other active ingredients. Hypericin may be found throughout the plant but is typically found in greatest concentration in the yellow flowers.

This plant has been used medicinally for over 2000 years. It has been touted as a remedy for bruises, skin inflammation, wounds and burns and has been used in diarrhoea, bed-wetting, bronchitis, muscle pains and whole lot of other ailments. Recently, researchers are even studying its use in acquired immune deficiency syndrome (HIV) patients.

The Herb's Role As An Antidepressant
St. John's Wort has gained much attention for its use in the treatment of depression. In Germany, where doctors routinely prescribe herbal remedies, St. John's wort is the most common form of antidepressant prescribed for mild to moderate depression -- more widely used than the drugs Prozac or Zoloft because it is cheaper and has fewer side effects. It is also gaining popularity as a natural remedy or neutraceutical.

0619cRandomised and controlled trials show that St. John's Wort is superior to placebo in treating mild to moderate depression. It is believed to combat depression by boosting the levels of certain chemical messengers in the brain.

It works on two fronts. Firstly, it seems to increase the amount of serotonin available to the nervous system (similar to Prozac). Secondly, it is thought to promote higher levels of dopamine like the monoamine oxidase (MAO) inhibitors.

Using St John's Wort
St. John's Wort has been shown to help with the symptoms of anxiety, fatigue, and of course, the general feelings of sadness and hopelessness. Other effects like decreased sex drive, weight fluctuation and insomnia or hypersomnia resulting from depression also benefit from the use of the herb.

1) Dosage

As St. John's Wort is a herbal medicine, there is no standardised method of preparation unlike the prescription medicines. Thus consumers should study the content of each capsule carefully. It is sold in bottles containing hypericin ranging from 0.125% to 0.3% hypericin but 0.3% hypericin is the commonly cited concentration.

The general dosage is to take it 3 times a day with each dose being 300 milligrams of 0.3% hypericin extract. To avoid missing doses, you can also simplify the regimen by taking two 300 mg capsules in the morning and one in the evening (or vice versa).

2) Side effects and cautions

St. John's Wort is known to increase one's sensitivity to sunlight. Thus to avoid a sunburn, minimise exposure to sun while using this medication. Also, avoid taking this herb with other medications that have the same effects such as tetracycline and fluoroquinolone antibiotics.

Drug interactions
As the herb's exact mechanism of action is still unclear, it is not advisable to combine it with MAO inhibitors (which are really antidepressants of last resort and the most risky) and medications prescribed for Parkinson's disease. Also, if conventional antidepressant like Prozac and Zoloft have been prescribed, do not start taking St. John's Wort without first consulting your doctor. Although rare, serious adverse reactions have been reported from such combinations.

Recent study documented a significant drug interaction between St. John's Wort and indinavir, a protease inhibitor used to treat HIV infection. In this study, concomitant administration of St. John's wort and indinavir substantially decreased indinavir plasma concentrations. This is potentially due to induction of the cytochrome P450 metabolic pathway by St. John's Wort.

Based on this study and reports in the medical literature, St. John's wort may potentially interact with other prescription drugs that are metabolised via the cytochrome P450 pathway, which means it can reduce the presence and potency of a prescription in the bloodstream. If you are on any drug used to treat conditions such as heart disease, depression, seizures and certain cancers or to prevent conditions such as transplant rejection or even oral contraceptive pills, you should be very careful about using the herb.

Because of the long list of prescription drugs the herb can interact dangerously with, it's important not to start on the herb until you've checked with your doctor.

Use in pregnant women, children and adolescents
Though no adverse effects have been reported in pregnant or lactating women using the herb, there have been few studies on this group, so caution is advised. St. John's Wort is not recommended for children except under strict physician care but it has been found to be incredibly effective in adolescents, which are often a very complicated group to treat. As there is evidence that more young adults and teens are popping pills in the search for a perfect body - even a feeling of well being - you should take the lead in setting a responsible example.

Care before surgery
There is some concern also that the herb may interact with anaesthesia and prolong their effects. So if you do have a habit of taking herbal remedies, make sure you tell your doctor.

0619bHow Long Should St. John's Wort Be Taken?
St. John's Wort takes two to six weeks to take full effect. If there is no improvement, it could signify that a different therapy for the condition is needed. On the other hand, there is no concrete scientific evidence on its long term effects so prolonged use is not advisable.

The jury is still out as to how effective St John's Wort actually helps people with depression. In fact, the dangers of self-prescription may far outweigh the gains in the long-term.

A Healthanswers clinical research consultant feels that the studies on the herb are not up to the calibre of proper clinical trials.

"Depression is nothing to fool around with, and this is my main concern about self-prescribing St. John's wort," she says. "There are too many physical illnesses that can be confused with clinical depression. People should always see their doctors first. While the use of [the herb] may be relatively benign, we just don't have any long-term studies to prove this in humans."


  1. Stevinson C. Ernst E. Hypericum for depression. An update of the clinical evidence. European Neuropsychopharmacology. 9(6): 501-5, 1999 Dec.

  2. Gaster B. Holroyd J. St. John's Wort for depression: a systematic review. Archives of Internal Medicine. 160(2):152-6, 2000 Jan

  3. Henney J. Risk of Drug Interactions with St John's Wort. JAMA. 283(13), 2000 Apr.

Date reviewed: 19 June 2000

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