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St. John’s Wort

By Melissa G. Marko, PhD, Senior Clinical Scientist, Nestle Nutrition ; Ara DerMarderosian, PhD, Professor Emeritus of Biology and Pharmacognosy, University of the Sciences

The reddish substance in the plant’s flowers contains numerous biologically active compounds, including hypericin and hyperforin.

Medicinal claims

People take St. John’s wort mostly to relieve symptoms of depression. Study results vary, but there may be a benefit in treating mild to moderate short-term depression.

St. John’s wort has been used in the treatment of skin disorders, including psoriasis, but its effectiveness in treating this disorder is unproved.

Possible side effects

St. John’s wort may cause increased sensitivity to sunlight. Other side effects include digestive tract symptoms, fatigue, and mania (in people with bipolar disorder). Pregnant women should not take this supplement because it increases muscle tone in the uterus and thus may increase the risk of a miscarriage.

Possible drug interactions

One of the larger problems with St. John’s wort is that it may interact negatively with a number of drugs people take (see Table: Some Possible Medicinal Herb–Drug Interactions). These interactions may lead to toxic reactions or ineffectiveness of the drug.

Drug Interactions With St. John's Wort

Affected Drugs

Interaction

Benzodiazepines

St. John’s wort may reduce the effectiveness of these drugs in reducing anxiety and may increase the risk of side effects such as drowsiness.

Cyclosporine

St. John’s wort may reduce blood levels of cyclosporine, making it less effective, with potentially dangerous results (such as rejection of an organ transplant).

Digoxin

St. John’s wort may reduce blood levels of digoxin, making it less effective, with potentially dangerous results.

Iron

St. John’s wort may reduce iron absorption.

MAOIs

St. John’s wort may intensify the effects of MAOIs, possibly causing very high blood pressure that requires emergency treatment.

Nonnucleoside reverse transcriptase inhibitors

St. John’s wort increases the metabolism of these drugs, reducing their effectiveness.

Oral contraceptives

St. John’s wort increases the metabolism of these drugs, reducing their effectiveness.

Photosensitizing drugs (such as lansoprazole, omeprazole, piroxicam, and sulfonamide antibiotics)

When taken with these drugs, St. John’s wort may increase the risk of sun sensitivity.

Protease inhibitors (such as indinavir or saquinavir), which are used to treat HIV infection

St. John’s wort may reduce blood levels of protease inhibitors, making them less effective.

Selective serotonin reuptake inhibitors (SSRIs, such as fluoxetine, paroxetine, and sertraline)

St. John’s wort may intensify the effects of these drugs.

Tricyclic antidepressants

May intensify the effects of these drugs.

Warfarin

St. John’s wort may reduce blood levels of warfarin, making it less effective and clot formation more likely.

More Information

Resources In This Article

Drugs Mentioned In This Article

  • Generic Name
    Select Brand Names
  • ZOLOFT
  • PRILOSEC
  • PREVACID
  • NEORAL, SANDIMMUNE
  • PAXIL
  • LANOXIN
  • INVIRASE
  • PROZAC, SARAFEM
  • FELDENE
  • COUMADIN
  • CRIXIVAN