St. John's Wort used primarily as a mild anti-depressant, St. John's Wort seems to be effective in elevating mood for the mild depression that often accompanies PMS.

What Is St. John's Wort?
St. John's Wort ( Hypericum perforatum) is an herbaceous, perennial medicinal plant which has been found to treat mild to moderate depression.

How does St. John's Wort work?
Extensive research here and in Germany has indicated that while not the only active component, hyperforin is certainly a major active component of hypericum extracts. Hyperforin antagonizes the activities of serotonin as well as other neurotransmitters. The more serotonin influencing cells in the brain, the more elevated the mood.