The flowers of St. John's wort contain its biologically active ingredients hypericin and hyperforin. St. John's wort may increase CNS serotonin and, in very high doses, acts like a monoamine oxidase inhibitor (MAOI).
Study findings are variable, but St. John's wort may benefit patients with mild to moderate depression who have no suicidal ideation. A large, well-designed study found it ineffective in treating major depression.
Dose is 300 to 600 mg po once/day of a preparation standardized to 0.2 to 0.3% hypericin, to 1 to 4% hyperforin, or to both (usually). St. John's wort is also said to be useful for treating HIV infection but has proven adverse interactions with protease inhibitors and nonnucleoside reverse transcriptase inhibitors (NNRTIs). A small trial showed St. John's wort (standardized to hypericin but not hyperforin) did not relieve symptoms of attention-deficit/hyperactivity disorder in children.
Photosensitivity, dry mouth, constipation, dizziness, confusion, and mania (in patients with bipolar disorder) may occur. St. John's wort is contraindicated in pregnant women. Potential adverse interactions occur with cyclosporine, digoxin, iron supplements, MAOIs, NNRTIs, oral contraceptives, protease inhibitors, SSRIs, tricyclic antidepressants, and warfarin.
Last full review/revision May 2009 by Ara DerMarderosian, PhD
Content last modified August 2013