St. John's Wort is believed to combat depression by boosting the levels of certain chemical messengers in the brain. Like the prescription antidepressant Prozac it seems to increase the amount of serotonin available to the nervous system.

Kosher St John's Wort [Kof K]

It also tends to promote higher levels of the chemical messengers norepinephrine and dopamine. In some clinical trials, daily doses of 800 to 900 milligrams of St. John's Wort have proven to be as effective as 20 milligrams of Prozac or 75 milligrams of the antidepressant Tofranil.