Barrett, B., Kiefer, D., & Rabago, D. (1999).  Assessing the risk and benefits of herbal medicine: an overview of scientific evidence. Alternative Therapies, 5(4):40-49.

Echinacea vs. the Common Cold, (2000).  Harvard Womens Health Watch, 7(6)1.

Ertel, G. (1999).  Information on additional Echinacea trials, Journal of Family Practice, 48(12):1001-2.

Jellin, J. (1999.  Prescriber's Letter: Therapeutic Uses of Herbs I, Stockton, California.

Kuhn, M. (1999).  Complementary Therapies for Health Care. Lippincott William & Wilkins,  Philadelphia, Pennsylvania. 

Muirhead, G. (1999).  Herbal medicines you can recommend with confidence, Patient Care, Sept. 75, 94

Ness, J. (1999).  Alternative medicine: what the data say about common herbal therapies, Geriatrics, 54(10):33-8, 40, 43.