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St. John's Wort Fact Sheet

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Medication Name (brand): 
St. John's Wort
Medication Name (clinical): 
St. John's Wort

Not regulated by the FDA, considered a dietary supplement.

  • Mechanism of psychiatric effect is unclear. Active antidepressant ingredients likely

  • are hypericin and/or hyperforin. Both may inhibit the reuptake of serotonin, norepinephrine, and
  • dopamine, but other neurochemical effects have been suggested as well.

  • Usual dose is 300 mg TID.

  • • The standard preparation used to be 0.3% hypericin, but now manufacturers are offering
  • products standardized to 2% to 6% hyperforin, since many believe hyperforin is the most
  • important antidepressant component.


Assuming 900 mg QD, the cost is usually in the range of 50 cents to $1 per day.

Evidence of Efficacy: 
  • Major Depression: About 30 randomized, double blind controlled trials have shown

  • antidepressant efficacy, but most of these were published in European journals. U.S. trials
  • have been mixed.

What Is It?: 

St. John’s Wort is a flowering herb (Hypericum perforatum) that blooms around
June 24 (St. John’s Day).

Side Effects: 
  • Rate of side effects similar to placebo and lower than standard antidepressants in

  • controlled trials. Mild GI side effects and sedation are possible. Photosensitivity in fairskinned
  • people. Switch to mania has been reported. No sexual side effects.

Drug-drug Interactions: 
  • Probably induces the 3A4 isoenzyme of the P450 family of hepatic enzymes.

  • • May decrease levels of the following drugs: cyclosporin (an immunosuppressive),
  • indinavir (a protease inhibitor), warfarin, theophylline, digoxin, and oral contraceptives.
  • • May cause serotonin syndrome in combination with SSRIs, but this is rare.
  • • Little information is available on interaction with MAOIs, but most authorities
  • recommend avoiding this combination.

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