A review of clinical and experimental observations about antidepressant actions and side effects produced by Hypericum perforatum extracts.

Hypericum perforatum is an herbaceous perennial plant, also known as "St. John's wort", used popularly as a natural antidepressant. Although some clinical and experimental studies suggest it has some properties similar to conventional antidepressants, the proposed mechanism of action seems to be multiple: a non-selective blockade of the reuptake of serotonin, noradrenaline and dopamine; an increase in density of serotonergic and dopaminergic receptors and an increased affinity for GABAergic receptors; moreover, the inhibition of monoaminoxidase enzyme activity has been involved. In any case, the increase of monoamine concentrations in the synaptic cleft resembles several actions exerted by clinically effective antidepressants. In the present article, we review some of the controversial evidence derived from clinical and experimental studies suggesting that H. perforatum exerts antidepressant-like actions, and we also review some of its side effects, such as nausea, rash, fatigue, restlessness, photosensitivity, acute neuropathy, and even episodes of mania and serotonergic syndrome when administered simultaneously with other antidepressant drugs. All of the foregoing suggests that H. perforatum extracts appear to exert potentially significant pharmacological activity involving several neurotransmission systems supposed to be involved in the pathophysiology of depression. However, little information regarding the safety of H. perforatum is available, including potential herb-drug interactions. There is a need for additional research on the pharmacological and biochemical activity of H. perforatum, as well as its side-effects and its several bioactive constituents to further elucidate the mechanisms of antidepressant actions.