Clinical Question Are Echinacea products associated with a reduced incidence and a shorter duration of common colds compared with placebo?
Bottom Line Individual prophylaxis trials show no association with prevention of the common cold, but exploratory meta-analysis suggests that Echinacea products may be associated with a small reduction in cold incidence. In treatment trials, there was no association of Echinacea products with a shorter duration of colds.
Preparations of the plant Echinacea are widely used in North America and Europe for prevention and treatment of the common cold.1 This JAMA Clinical Evidence Synopsis summarizes the results of a Cochrane review2 regarding the association ofEchinacea products with prevention and treatment of colds.
Marlies Karsch-Völk, MD1; Bruce Barrett, MD, PhD2; Klaus Linde, MD1
No. of randomized clinical trials: 24 (33 comparisons of Echinacea and placebo; 14 treatment trials, 9 prevention trials, 1 trial examining both prevention and treatment); 1 trial included only children.
Study years: Conducted, 1990-2010; published, 1992-2012
No. of patients: 2809 in treatment trials, 1822 in prevention trials
Men: 1640 (42%) Women: 2294 (58%) (sex not reported in 5 trials)
Age, mean: 27.9 years (age not reported in 5 trials)
Settings: Variety of inpatient and outpatient settings
Countries: United States, Sweden, Germany, Canada, United Kingdom, Australia
Comparison:Echinacea vs placebo
Primary outcome: Cold duration in days for treatment trials; number of participants with at least 1 cold for prevention trials
Using the Cochrane “risk of bias” tool, 10 trials had a low risk of bias, 8 trials had a high risk of bias, and 6 trials had an unclear risk of bias. Because the trials studied chemically diverse extracts of Echinacea, we made an a priori decision not to pool data in a meta-analysis. Nevertheless, to provide a crude estimate of overall results and to generate hypotheses for future testing, we pooled study findings when there was no indication of statistical heterogeneity.
Ten trials investigated the prevention of colds. Nine of these (with 12 comparisons of an Echinacea product and placebo) reported the number of patients with at least 1 cold. None of the individual trials found a significant association of Echinacea with a reduction of colds (Figure). As findings were highly consistent (I2 = 0%, τ2 = 0.00), we pooled all 9 trials, regardless of the product used. Among these trials, an exploratory meta-analysis showed that prophylactic treatment with Echinacea products was associated with a lower rate of colds, 285 of 666 patients in the Echinacea group vs 279 of 501 patients in the placebo group (risk ratio, 0.83 [95% CI, 0.75-0.92]; P < .001
Figure. Risk Ratios for Participants With at Least One Cold Episode In the Prevention Trials Source: Data have been adapted with permission from Wiley.2 The analysis includes 9 trials with 12 comparisons of an Echinacea product and placebo with a total of 1167 patients. Melchart, 1998, compared 2 distinct Echinacea products and Turner, 2005, 3 distinct Echinacea products with a placebo group.
Fifteen trials were treatment trials. Six of these reported on duration of cold symptoms. One with a high risk of bias and 1 trial with unclear risk of bias reported large, statistically significant associations of Echinacea with shorter duration of cold symptoms compared with placebo, whereas the 4 trials with low risk of bias did not find any associations of Echinacea with duration of cold symptoms. Due to the strong heterogeneity of findings and methodological quality, we did not include exploratory meta-analyses across trials or products on efficacy.
Most common adverse effects reported were headache, nausea, and a bad taste. In treatment trials, Echinacea products were associated with a higher rate of adverse effects (323 of 946 patients receiving Echinacea vs 281 of 863 patients receiving placebo; odds ratio [OR], 1.28 [95% CI, 1.02-1.60]; P = .03). In prevention trials, there was no association of Echinacea with adverse effects (102 of 868 patients receivingEchinacea vs 65 of 757 patients receiving placebo; OR, 1.49 [95% CI, 0.95-2.35]; P = .09). The treatment trial among children found that Echinacea was associated with a higher prevalence of rashes.
In individual trials, there was no association of Echinacea products with prevention of the common cold. However, exploratory meta-analysis across products suggests thatEchinacea products may be associated with a small reduction in cold incidence and that individual trials seem to be underpowered. The overall evidence for clinically relevant treatment effects is weak. We updated the search in July 2014, but could not identify more recent randomized clinical trials on Echinacea for preventing or treating the common cold.
A variety of products prepared from different Echinacea species, plant parts, and in different forms have been compared with placebo in randomized clinical trials. These preparations contain different amounts of bioactive components and hence are not biochemically similar. Preparations based on the aerial parts of Echinacea purpureawere investigated most often. Furthermore, trial approaches and methods for cold assessment were highly variable between studies. Therefore, trial results could not be combined for our primary outcome analyses. Publication bias cannot be ruled out with certainty.
Comparison of Findings With Current Practice Guidelines
Treatment of the common cold with Echinacea products is not specifically addressed in current guidelines and recommendations.3,4 Recommendations by the British National Institute for Health and Care Excellence (NICE)5 generally advise against the use of complementary and alternative medicine in cold treatment, without mentioning Echinacea products particularly.
Areas in Need for Future Study
Future studies should use well-defined preparations and a standard set of outcome measures in randomized clinical trials. Trials investigating the prevention of colds need large sample sizes as the potential effects of Echinacea products are likely to be small.