ask your pharmacist

back to: pharmacy | ask your pharmacist

Are there any interactions with St. John's Wort?

The herb St. John's wort (Hypericum perforatum) is widely used in treating mild to moderate depression. Extracts of St. John's wort contain some 50 different chemicals, and it's not yet clear which of them are responsible for the herb's activity. .

Although St. John's wort is generally considered a safe treatment, it does interact with various drugs. Researchers at the National Institutes of Health reported that St John's wort can significantly reduce the effectiveness of an antiviral drug that is often prescribed for patients with human immunodeficiency virus (HIV) infection. When people took St. John's wort and the protease inhibitor indinavir (brand name Crixivan) together, levels of indinavir in the blood dropped dramatically. This could allow a patient's virus infection to worsen or increase the odds that the virus will develop resistance to the drug.

Another recent study has found that St. John's wort can interfere with cyclosporine, a drug used to keep transplant patients from rejecting their new organs.

St. John's wort seems to change the way the body breaks down and removes indinavir and cyclosporine. Other drugs that may be similarly affected include other antiviral medicines, certain heart medicines, birth control pills, seizure medicines, antianxiety drugs, anticoagulant drugs such as warfarin (Coumadin), and anticancer drugs. The Food and Drug Administration (FDA) recommends that people who take any of these drugs consult their doctor before using St. John's wort. This list is not all-inclusive, so always be sure to talk to your doctor before taking herbal or alternative medicines.

In addition, don't combine St. John's wort with the prescription medicines piroxicam (brand name Feldene) or tetracycline (Sumycin). These combinations can make the skin very sensitive to sunlight and increase the chance of severe sunburn.

It's also wise to avoid taking St. John's wort along with other types of drugs and supplements as well, including prescription antidepressants, bromocriptine (Parlodel), pseudoephedrine (Sudafed), yohimbine (Yocon), or ma huang. In rare cases, these combinations may lead to headache, sweating, dizziness, muscle spasms, and increased blood pressure.

Sources:
Peirce, A. The American Pharmaceutical Association Practical Guide to Natural Medicines. William Morrow & Co., 1999.
The Review of Natural Products. Facts & Comparisons, 2007.
FDA Public Health Advisory. "Risk of Drug Interactions with St. John's Wort and Indinavir and Other Drugs". 2000.
Pistcitelli, S. "Indinavir Concentrations and St. John's Wort," Lancet 355 (2000).
Fugh-Berman, A. "Herb-drug Interactions," Lancet 355 (2000).
NIH News Release. "NIH Clinical Center Study Demonstrates Dangerous Interaction Between St. John's wort and an HIV Protease Inhibitor". Feb. 10, 2000.
Micromedex® Healthcare Series. Thomson Micromedex, 2007.

This answer prepared 1/17/2001.
This information updated 1/18/2007.