St Johnswort: How Fast Does It Work?

I am writing to ask what the herb St John's wort does. Can anyone take it and how long before you see the affect of the herb?

Christopher Hobbs has written an excellent book on St Johnswort which we strongly recommend called, "St. Johnswort, The Mood Enhancing Herb" (available from Richters). St. Johnswort is now best known for its antidepressant effect. Some have suggested that it is an effective herbal substitute for the drug Prozac. It also has many other effects related to its mood-enhancing effect; for example, it has long been used to treat insomnia. It is also known to have potent antiviral properties.
Hobbs says that St. Johnswort is very safe when used within normal recommended doses. It can cause photosensitivity in some individuals when taken in large doses. Because St. Johnswort is a weak monoamine oxidase (MAO) inhibitor, caution should be exercised when combining with other MAO inhibitors. Although there is no evidence to suggest any problem for pregnant and breast-feeding women, it should not be taken by these women without medical advice.
According to Hobbs' research, the antidepressant effect of St Johnswort does not become apparent right away; it can take up to 4 weeks before the effects on mood are noticed. It is not effective for all individuals; if no effect is noticed after 4 weeks, then St. Johnswort should be stopped.
Hobbs has much more information about how and when to take St. Johnswort in his book.