Although popular as an over-the-counter herbal treatment for the common cold, researchers say echinacea has no big impact and only reduces duration of symptoms by half a day at the most.
Lead researcher Dr Bruce Barrett, an associate professor of family medicine at the University of Wisconsin-Madison School of Medicine and Public Health in Madison, Wisconsin, USA, and colleagues, published their findings in the 20 December issue of Annals of Internal Medicine.
The botanical genus Echinacea, also known as purple coneflower, is a wild flower that is native to North America, where indigenous peoples have used it in various forms for a variety of illnesses. It became popular as a remedy for respiratory infection and other illnesses in the rest of the world after early research was done in Germany in the 1920s, wrote the authors.
Most commercially available echinacea products are made primarily from 2 species: Echinacea purpurea and E. angustifolia. Echinacea has been used in homemade remedies in the form of teas, dried herb and liquid extracts, and a supplement form is available as capsules sold in drug and retail stores. For this study, the researchers used a root-based preparation of the herb.
Barrett and colleagues wrote in their introduction that by the mid 1990s there were several hundred published studies on echinacea, including over a dozen randomized trials, nearly all reporting benefits for treating the common cold, but all were “manufacturer-sponsored and of moderate to poor quality”.
Since then there have been several trials, some with positive results, and some with negative results, including one by Barrett and his team, which also produced negative results. Systematic reviews on these studies also varied in their results and interpretation.
“We designed and conducted this trial because the effectiveness of echinacea was still unclear,” wrote the authors.
The primary funding for this trial came from the National Center for Complementary and Alternative Medicine, which is part of the National Institutes of Health in the US.
Barrett and colleagues recruited 719 volunteers aged from 12 to 80 (average age 33.7 years, 64% female, 88% white), all of whom had very early symptoms of a cold. 713 of the volunteers completed the study.
They divided the participants into four “parallel” groups. The first group received no pills at all, the second group received echinacea and knew it was echinacea (“non-blinded echinacea” group), and the other two groups received either echinacea or placebo but they did not know which (the “blinded echinacea” and the “blinded placebo” groups).
The echinacea groups received the equivalent of 10.2 g of dried echinacea root during the first 24 hours, and then 5.1 g for each of the following 4 days. The placebo pills looked exactly the same as the echinacea pills but contained only inert ingredients.
The participants recorded their symptoms on a Wisconsin Upper Respiratory Symptom Survey (WURSS short version) twice a day for as long as symptoms persisted, up to two weeks.
The researchers also assessed measures of immune response (interleukin-8 levels and neutrophil counts) from nasal wash taken at the start and 2 days later.
The researchers described their results as follows:
- Mean global severity (an overall score on the symptom survey) was 236 for the blinded and 258 for the unblinded echinacea group, 264 for the blinded placebo group, and 286 for the no-pill group.
- A comparison of the blinded placebo versus the blinded echinacea group showed a “28-point trend” toward benefit for the latter (95% confidence interval CI ranged from -69 to 13 points, P = 0.089).
- The mean duration of illness in the blinded echinacea group was 6.34 and in the unblinded echinacea group was 6.76 days.
- This compared with 6.87 days in the blinded placebo group and 7.03 days in the no-pill group.
- A comparison of the blinded groups showed a “nonsignificant 0.53-day benefit” for echinacea (95% CI -1.25 to 0.19 days, P=0.075).
- “Median change in interleukin-8 levels and neutrophil counts were also not statistically significant”.
They concluded that:
“Illness duration and severity were not statistically significant with echinacea compared with placebo.”
These results do not support the ability of this dose of the echinacea formulation to substantively change the course of the common cold,” they added.
Barrett told the media that in their study, patients receiving echinacea saw the duration of their cold reduced by seven to 10 hours, but this was not statistically significant compared to placebo.
He said although the trend was in the “direction of benefit”, amounting to an average of half a day reduction in the duration of a week-long cold, or about 10 per cent reduction in overall severity of symptoms, the dose regime they used on the study “did not make a large impact on the course of the common cold, compared either to blinded placebo or to no pills”.
Barrett said based on their trial, there was no reason to stop using echinacea if you find it helps:
“Adults who have found echinacea to be beneficial should not discontinue use based on the results of this trial, as there are no proven effective treatments and no side effects were seen,” he explained.
The researchers suggest there should now be a larger trial with more participants who have found echinacea useful.
“Echinacea for Treating the Common Cold: A Randomized Trial.”
Bruce Barrett, Roger Brown, Dave Rakel, Marlon Mundt, Kerry Bone, Shari Barlow, and Tola Ewers.
Annals of Internal Medicine, Vol 153, No 12, pp 769-777 , 20 December 2010.
Additional Source: University of Wisconsin-Madison.