Guide to Herb Usage

I have recently become interested in using herbs for a variety of reasons. My problem is I have started using them then stop then start up again. I've done this using the Echinacea Tea, St. John's Wort and have even started using the Essiac teas. What has never been clear to me in using herbs is how long should one take them. Daily, forever? For example, I am interested in taking Ginkgo Biloba, Ginseng and a few others but don't know if they should be taken daily or not. Can you please advise me on this. Also, is there a book that gives one a guideline as to what they might consider taking, how much, how often.

Some herbs may be taken as tonics, much like food, to nourish the various body systems and prevent disease. The herbal medicine approach is holistic, suggesting that you look first to your lifestyle - diet, exercise, relationships, emotional well being and spiritual practices which contribute to health and disease. Where there are weaknesses, tonic herbs can help to strengthen. David Hoffman, in "The New Holistic Herbal" (Element Publisher, Rockport Massachusetts) suggests the following can be taken as preventatives for extended periods of time: Hawthorn Berries for the circulatory system, Mullein for the Respiratory system, Meadowsweet for the digestive system, Skullcap for the Nervous system, Nettles for the skin, Celery seed for the Muscular and skeletal system, Raspberry leaves for the reproductive system, and Buchu for the Urinary system. While taking the tonic herbs, they are best taken on a daily basis. Once the body is back in balance, there may not be a need for the particular herb you have been using.
For particular illnesses , you should consult a herbalist or naturopath for treatment rather than self diagnose. Herbs, like food and drugs, do have a physiological effect, and if taken in excess or for prolonged periods of time, can influence the body's natural roles in self healing. The goal in herbal treatment is to bring the body into balance so that the herbs are no longer required. The particular herbs that you are asking about should be taken only for specific conditions. When herbs are used therapeutically, they are to be taken daily, ususally 3 times a day. Because they exert a more gentle and longer lasting effect than drugs, it sometimes takes 2 or 3 weeks before an appreciable improvement in the condition is noticed.
A guidebook that will give you more information is "The Encyclopedia of Medicinal Plants" by Andrew Chevallier (available at Richters).