I'm taking prescription drugs. Should I use St. John's Wort?

A lot of confusion surrounds the correct use of St. John's Wort. The herb is traditionally prepared from the flowering tops of the plant. It is only since drugs companies have been extracting, purifying and concentrating one of the herb's constituents, hypericin, that adverse effects such as photosensitivity have been observed in some people when taking the extract. All the clinical trials purporting to show adverse effects have been carried out on this concentrated extract, and not on the traditional preparation.

Hypericin (in isolation) can have one of two effects when you are taking prescription drugs, depending on the drug. These effects have to do with the way hypericin acts on the liver:

(1) The drug's effects can be enhanced - because the presence of hypericin encourages the drug to stay in your bloodstream for longer.

(2) The drug's effects can be reduced - because the presence of hypericin boosts your liver's ability to excrete the drug - which it perceives as a toxin - more quickly. (Note that this is actually a beneficial action by hypericin on the liver!)

Obviously, if you are taking drugs for a life-threatening condition, you do not want either of these effects to occur.

The major drugs whose effects may be enhanced by hypericin are as follows:

  • Antidepressants
  • Warfarin

The major drugs whose effects may be reduced by hypericin are as follows:

  • AIDS treatments
  • Contraceptive pill
  • Drugs taken to prevent rejection of transplanted organs

As with all herbs, the best way to take St. John's Wort is in the traditional form, using the whole plant part. The beneficial effects of hypericin are still there, but the risk of side effects is minimised by the presence of buffering substances in the plant. Ask one of the professional herbalists for advice in your individual case.

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