Health Canada April 7, 2000
2000-36
April 7, 2000
Advisory
Potentially harmful
drug interaction with St. John's Wort and prescription drugs
OTTAWA - Health Canada is advising health care professionals and
consumers of the potential for drug interaction when certain prescription
medications are used in combination with St. John’s Wort (Hypericum
perforatum). St. John’s Wort is a natural health product promoted as a treatment for
mild depression or as a sedative. Drug interaction can seriously alter or
diminish the effectiveness of the prescription medication.
A recent clinical trial, published in the medical publication
Lancet, showed that St. John’s Wort, when administered in
conjunction with indinavir, a protease inhibitor used to treat HIV
infection, significantly decreased the protease inhibitor’s presence in
the blood stream. With such a decrease, the drug becomes considerably less
effective and may promote the development of viral resistance to the drug.
Because some other AIDS drugs are metabolized in a similar way to
indinavir, the possibility of interactions with these drugs should also be
considered.Therefore, those patients currently using St. John’s Wort
concurrently with any antiretroviral drug are strongly urged to consult
their health care practitioner.
Other evidence shows that St. John’s Wort could also affect the
metabolism of a variety of prescription drugs, including anti-epilepsy
agents, oral contraceptives, immuno-suppressants such as cyclosporine,
antidepressants, and anticoagulants. In certain cases, use of St. John’s
Wort by transplant patients has been associated with acute organ
transplant rejection in conjunction with a decrease in cyclosporine values
in the blood stream below the therapeutic range.
Consumers are also advised that use of St. John’s Wort in conjunction
with conventional antidepressants may cause "serotonin syndrome", an
excess of serotonin which can cause tremors, headaches and restlessness.
It should be noted that, when used on its own, St. John’s Wort has not
demonstrated significant health risks.
Health Canada has issued a letter to Canadian physicians, pharmacists, and
practitioners of complementary medicine [letter in PDF format],
alerting them to the possibility of drug interactions with
St. John’s Wort. Consumers of St. John’s Wort products are advised to
notify their health care practitioner before continuing or beginning
conventional drug therapy.
The text in this article was prepared by Health Canada.