CRD summary

This review concluded that the potential therapeutic effectiveness of echinacea in the treatment of the common cold has not been established. The review provided limited information on the review methods and included studies. These limitations make it difficult to assess whether the authors' conclusion is an accurate reflection of all the available evidence, and its reliability is unclear.

Authors' objectives

To examine the use of echinacea for the treatment of the common cold.

Searching

MEDLINE and PubMed were searched from 1966 to 2003 using the reported search terms. In addition, previous relevant reviews were checked for additional studies.

Study selection

Assessment of study quality

Validity was assessed according to 11 criteria: validated case definition, quantifiable hypothesis, sample size calculation, random assignment, double-blinding, measurement of compliance, measurement of drop-out rate, intention-to-treat analysis, methods of statistical analysis, and p-values and confidence intervals (CI) provided. The authors did not state how the validity assessment was performed.

Data extraction

The authors did not state how the data were extracted for the review, or how many reviewers performed the data extraction. The studies were categorised as finding a positive or negative result, as judged by the investigators conducting the work.

Methods of synthesis

Results of the review

Nine placebo-controlled trials (number of participants unclear) were included in the review.

Two studies fulfilled all 11 quality criteria, one study met 10 criteria, one 8 criteria, one 7 criteria, two 6 criteria, one 5 criteria and one 3 criteria. Seven studies lacked proof of blinding. Half of the studies did not include a quantifiable hypothesis, sample size calculation, measurement of compliance, description of methods of randomisation or similarity of groups, or provide validated case definitions. The studies that fulfilled all 11 criteria had negative results. Of the remaining studies, all but one had positive results. The study which met 10 quality criteria and found a positive result lacked proof of blinding.

Authors' conclusions

The potential therapeutic effectiveness of echinacea in the treatment of the common cold has not been established.

CRD commentary

The authors set out an objective at the beginning of the review, but the inclusion criteria were broad and were not defined for study outcomes. Few sources were searched, thereby increasing the likelihood that relevant studies might have been missed. Furthermore, it was unclear whether the search was restricted by language or publication bias. The authors did not report the methods used for the study selection, quality assessment or data extraction, which means that the possibility of bias in these processes cannot be assessed. Validity was assessed using appropriate criteria and the results were presented clearly.

Few study details were provided. The narrative synthesis seemed appropriate given the differences between the studies. However, the studies were simply categorised as finding a positive or negative result, with few details of the specific outcomes that had been assessed. This review provided very limited information about the review methods and included primary studies. These limitations make it difficult to assess whether the authors' conclusion is an accurate reflection of all the available evidence, and its reliability is unclear.

Implications of the review for practice and research

Practice: The authors did not state any implications for practice.

Research: The authors stated that further well-designed trials assessing the effectiveness of echinacea in the treatment of the common cold are required.

Bibliographic details

Caruso T J, Gwaltney J M. Treatment of the common cold with echinacea: a structured review. Clinical Infectious Diseases 2005; 40(6): 807-810. [PubMed: 15736012]

Indexing Status

Subject indexing assigned by NLM

MeSH

Common Cold /drug therapy; Echinacea /chemistry; Humans; Phytotherapy; Plant Extracts /chemistry /therapeutic use; Reproducibility of Results

AccessionNumber

12006003775

Database entry date

31/10/2007

Record Status

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.