Rutin is essential for the antidepressant activity of Hypericum perforatum extracts in the forced swimming test.

It has been shown that aqueous alcoholic extracts of Hypericum perforatum (St. John's wort) are active in the forced swimming test (FST), an animal model for antidepressant activity. In this study, a series of ethanolic and methanolic extracts were investigated and, in almost all cases, the extracts showed strong activity. Only one methanolic research extract had no effect in the in vivo pharmacological experiments. Analytical characterisation using HPLC showed that the inactive extract had a reduced level of the diglycoside flavonoid rutin. Addition of rutin to the inactive extract, to produce a concentration within the normal range, resulted in a strong pharmacological effect comparable to that of the other extracts. First experiments suggest that this re-activation is not dose-dependent, indicating that rutin must be present above a threshold limit. It therefore appears vital that extracts of St. John's wort which are designed for the therapy of depressive disorders should be manufactured using plant material with sufficient amounts of rutin.