St John's wort (Hypericum perforatum L.): a review of its chemistry, pharmacology and clinical properties

The chemical composition of St. John's wort has been well-studied. Document ed pharmacological activities, including antidepressant, antiviral, and ant ibacterial effects, provide supporting evidence for several of the traditio nal uses stated for St John's wort. Many pharmacological activities appear to be attributable to hypericin and to the flavonoid constituents; hyperici n is also reported to be responsible for the photosensitive reactions that have been documented for St. John's wort. With regard to the antidepressant effects of St John's wort, hyperforin, rather than hypericin as originally thought, has emerged as one of the major constituents responsible for anti depressant activity. Further research is required to determine which other constituents contribute to the antidepressant effect. Evidence from randomised controlled trials has confirmed the efficacy of St John's wort extracts over placebo in the treatment of mild-to-moderately s evere depression. Other randomised controlled studies have provided some ev idence that St John's wort extracts are as effective as some standard antid epressants in mild-to-moderate depression. There is still a need for furthe r trials to assess the efficacy of St John's wort extracts, compared with t hat of standard antidepressants, particularly newer antidepressant agents, such as the selective serotonin reuptake inhibitors (recent comparative stu dies with fluoxetine and sertraline have been conducted). Also, there is a need for further studies in well-defined groups of patients, in different t ypes of depression, and conducted over longer periods in order to determine longterm safety. St John's wort does appear to have a more favourable shor t-term safety profile than do standard antidepressants, a factor that is li kely to be important in patients continuing to take medication. Concerns have been raised over interactions between St John's wort and cert ain prescribed medicines (including warfarin, ciclosporin, theophylline, di goxin, HIV protease inhibitors, anticonvulsants, selective serotonin reupta ke inhibitors, triptans, oral contraceptives); advice is that patients taki ng these medicines should stop taking St John's wort, generally after seeki ng professional advice as dose adjustment of conventional treatment may be necessary.