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Echinacea treatments for colds

One of the problems with complementary therapies is the absence of high quality trials. Systematic reviews that include poor quality trials have a propensity to mislead, because poor trials are often more positive in their outcomes. The best and most recent systematic review for echinacea treatment [1] had nine trials (1,264 subjects) assessing cold treatment with echinacea with a number of different products. The studies assessed patients over different duration (8 days to resolution of symptoms). Six trials showed modest, but significant improvement in symptoms over placebo (or vitamin C).

Despite this the beneficial effects of echinacea for the early treatment of colds were modest and there was no convincing evidence of its effectiveness in the prevention of colds. The trials were generally of medium to poor quality, though they were mostly of reasonable size (over 100 patients per group).

With this background, we should examine any new high quality trial to see whether it enhances or deflates the modest claims of efficacy. One such study [2] is highly deflating.


The study was properly randomised, properly blinded, and told us what happened to each patient in some detail. Treatments, active and placebo, were tested on volunteers to see if they could tell the difference - they could not. The paper is a model of reporting quality. In addition, the echinacea used in the study was subjected to chemical and biological activity, so that we know that it had active ingredients, and that those active ingredients caused expected changes in biological systems.

Participants were students at a US university recruited over a winter cold season. Advertisements asked respondents to call a number at the first sign of flu-like symptoms. These were screened first by telephone, and then by interview, all within a few hours of first contact. To be included subjects had to be over 18 years, to suspect they were coming down with a cold, to report at least two of 15 symptoms, one of which had to be specific to the respiratory tract, and to be willing to adhere to the protocol. Exclusions were symptoms established for more than 36 hours, pregnancy, and current use of antibiotics, antihistamines or decongestants.

The primary outcomes were the severity and duration of self-reported symptoms, collected both by paper and web-based instruments. The study was powered to detect a two-day difference in duration or a two point (out of four) difference in severity.


There were 148 participants (mean age 21 years), and echinacea and placebo groups were well matched, including use of non-protocol medicines. Information collection was almost 100% and adherence to tablets was 92% by counting returned bottles.

There was no difference in cold duration (Figure 1), which ranged from two to 10 days. It was 5.8 days for placebo and 6.3 days for echinacea.

Figure 1: Cold duration with echinacea and placebo

There was no difference in severity of any of 15 symptoms or of global severity at any time.

Some adverse events were reported by both groups (22 in 15 participants), with no difference between the groups.


Echinacea had absolutely no effect in this trial. Why not? Perhaps because echinacea does not work. Systematic reviews of generally low quality trials that probably have some bias can only show a modest effect, and this high quality study erodes that even further.

Three species of Echinacea are used in medicine: purpurea, angustifolia and pallida. It contains flavonoids, glycoproteins and a variety of other active components which are thought to stimulate the immune system. Extracts can be derived from the whole plant, roots or flowers and other plant extracts or homeopathic compounds may be added. The specific combination in this trial was purpurea whole plant and angustifolia root.

It is possible that there are other combinations that might yet have a modest effect, perhaps in other populations than young, otherwise healthy, undergraduates. But don't bet on it. Right now the best evidence is that echinacea is useless, and money spent on it is wasted.


  1. B Barrett et al. Echinacea for upper respiratory infection. Journal of Family Practice 1999 48: 628-635.
  2. BP Barrett et al. Treatment of the common cold with unrefined echinacea. A randomised, double-blind, placebo-controlled trial. Annals of Internal Medicine 2002 137: 939-946.
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