Echinacea for the Prevention and Treatment of Colds in Adults: Research Results and Implications for Future Studies
Updated October 2005
On July 28, 2005, The New England Journal of Medicine published the results of a study of Echinacea for the prevention and treatment of the common cold that was funded by the National Center for Complementary and Alternative Medicine (NCCAM).1 The research was conducted by Dr. Ronald Turner, of the University of Virginia School of Medicine, Dr. Rudolf Bauer, Karl-Franzens Universitaet, Graz, Austria, and collaborators at Clemson University in South Carolina.
The research team tested three preparations of the roots of a species of Echinacea called Echinacea angustifolia, which prior smaller studies had found to benefit adults with the common cold. The three preparations were made by extracting the root of E. angustifolia using procedures that represent some of the different ways that Echinacea is available and used to treat the common cold.
E. angustifolia was chosen for the study as it is one of the species endorsed by the World Health Organization for treating the common cold.2 The study was designed to test if Echinacea would help prevent or treat cold symptoms, since this is how Echinacea is often used by consumers.
In the study, 437 healthy adult volunteers were assigned at random to receive one of the three E. angustifolia preparations or a placebo. The volunteers received various combinations of Echinacea and/or a placebo in two phases: a “prophylaxis” (i.e., preventative) phase and a treatment phase. The prophylaxis phase lasted 7 days. On the seventh day, the already treated volunteers were exposed to a nasal spray containing a virus that induces signs and symptoms of a cold in about 2 days. Then, the volunteers were isolated for 5 days while the research team observed and tested them, using state-of-the-art measurements and instruments, as to the appearance and severity of cold signs and symptoms.
In this study, the researchers found that none of the three preparations of E. angustifolia at the 900 mg per day dose had significant effects on whether volunteers became infected with the cold virus or on the severity or duration of symptoms among those who developed colds. However, critics of this study believe the dose of E. angustifolia used was too low.
Research Design Challenges
Research on botanicals and other natural products presents a number of challenges related to product characterization, standardization, and dosage. For Echinacea, these challenges include:
- determining whether the roots, leaves, flowers, seeds, or stems are the most effective parts of the plant,
- investigating the differences between the major Echinacea species (E. purpurea, E. angustifolia, and E. pallida), and
- determining the proper dose.
It is only after these questions have been answered and standardized preparations have been developed that additional large-scale Phase III clinical trials can be conducted.
NCCAM’s strategy to guide the design and conduct of research on biologically active products through an integrated series of studies is more fully articulated at nccam.nih.gov/research/policies/naturalproduct.htm.
NCCAM Research on Echinacea Is Ongoing
NCCAM will continue to support research on Echinacea. A number of preclinical, Phase I, and Phase II studies of Echinacea products are currently under way. This research is being done both because of the public health burden of the common cold and the public’s widespread use of this natural product. A recent survey of complementary and alternative medicine use by adults in the United States found that, among those who reported using natural products, Echinacea was the most commonly used.3
- 1Turner RB, Bauer R, Woelkart K, et al. An evaluation of Echinacea angustifolia in experimental rhinovirus infections. The New England Journal of Medicine. 2005 353(4): 341–348.
- 2WHO monographs on selected medicinal plants. Vol 1. World Health Organization 1999:125–35.
- 3Barnes P, Powell-Griner E, McFann K, Nahin R. CDC Advance Data Report #343. Complementary and alternative medicine use among adults: United States, 2002. May 27, 2004.