The preparations enhance mood over a long period of time, generally not producing positive results for at least two to three weeks, and often taking two to three months before producing beneficial results. This shows one of the general differences traditionally recognized for herbal medicines. How it works A number of recent studies have focused on the pharmacological mechanisms and clinical use of St. John's wort for the treatment of depression. A 1984 study by Suzuki and co-workers demonstrated that hypericin, a red component abundant in the flowers of St. John's wort, inhibited type A and type B monoamine oxidase. Monoamine oxidase inhibitors have been used for the treatment of depression because they help to curb an enzyme that breaks down monoamine, which is a precursor of norepinephrine, a neurotransmitter.
Neurotransmitters carry nerve impulses through particular nerve pathways.
It has been suggested that some types of clinical depression may results from a decrease in the effectiveness of neurotransmitters in the brain. A and B monoamine oxidase, it was suggested as a possible basis for the anti-depressant activity of the plant, though the results are not conclusive. Other mechanisms of action could be involved. While many St. John's wort products available in both the European and American market are standardized to hypericin, this compound has not been unequivocally linked to the herb's antidepressant activity. While some studies suggest that hypericin or hypericin-like compounds may be linked to antidepressive activity, those conclusions have recently come into question.