Echinacea for Upper Respiratory Infections

CLINICAL QUESTION: Is Echinacea beneficial for the prevention or treatment of acute upper respiratory infections (URIs)?

BACKGROUND: Echinacea, taken for the prevention and treatment of URIs, is one of the most commonly used herbs. The goal of the authors of this study was to systematically review the randomized trials of Echinacea for the prevention or treatment of acute URIs.

POPULATION STUDIED: The authors reviewed the evidence from blinded placebo-controlled randomized trials of any formulation of Echinacea used for prevention or treatment of URIs. The study populations varied, and most were in Europe.

STUDY DESIGN AND VALIDITY: The authors identified studies by searching MEDLINE and other bibliographic reference services using variants on the term “Echinacea.” They also reviewed articles, books, and book chapters for references. They questioned herbal medicine experts in the United States and Germany about published and unpublished trials. Study quality was evaluated using the following criteria: randomization, blinding, power, validity, clinical relevance of outcome measurements, inclusion and exclusion criteria, indistinguishability between treatment and placebo, and appropriateness of conclusions. The authors went to great lengths to identify relevant studies, and it seems unlikely that any pertinent studies would have been missed. The authors do not describe how the quality considerations were scored or if they were reproducible. They state that meta-analysis (using statistical methods to combine data from different studies into a single summary measure of effect) was not an appropriate option because of the variations in preparations, methods, and outcomes measured. Even without meta-analysis, this is a good systematic review of the evidence for Echinacea for the prevention and treatment of URIs.

OUTCOMES MEASURED: The outcomes used in the treatment studies varied considerably. They included URI symptoms rated on a scale of 0 to 3, progression to a “real cold,” and the presence of influenzalike symptoms. Outcomes for the prevention trials included the time until the first URI and the severity of its symptoms.

RESULTS: The authors identified 13 blinded randomized trials. Nine of these studies were treatment trials, and 4 were studies of prevention. Eight of the 9 treatment trials reported a benefit. Six showed a statistically significant benefit, while 2 reported only a trend; the one study showing no benefit is unpublished and used insufficient doses of Echinacea. Data from one of the larger more methodologically sound studies¹ suggest that the number needed to treat to prevent a real cold among patients with the first sign of a cold was 5. Two of the prevention trials reported a marginal benefit: One initially reported a benefit but later reported no benefit, and one found no benefit. The major methodologic weaknesses identified included: lack of objective validated measures, no clear evidence that the treatment was indistinguishable from the placebo, and insufficient sample size.

CLINICAL QUESTION: Is Echinacea beneficial for the prevention or treatment of acute upper respiratory infections (URIs)?

BACKGROUND: Echinacea, taken for the prevention and treatment of URIs, is one of the most commonly used herbs. The goal of the authors of this study was to systematically review the randomized trials of Echinacea for the prevention or treatment of acute URIs.

POPULATION STUDIED: The authors reviewed the evidence from blinded placebo-controlled randomized trials of any formulation of Echinacea used for prevention or treatment of URIs. The study populations varied, and most were in Europe.

STUDY DESIGN AND VALIDITY: The authors identified studies by searching MEDLINE and other bibliographic reference services using variants on the term “Echinacea.” They also reviewed articles, books, and book chapters for references. They questioned herbal medicine experts in the United States and Germany about published and unpublished trials. Study quality was evaluated using the following criteria: randomization, blinding, power, validity, clinical relevance of outcome measurements, inclusion and exclusion criteria, indistinguishability between treatment and placebo, and appropriateness of conclusions. The authors went to great lengths to identify relevant studies, and it seems unlikely that any pertinent studies would have been missed. The authors do not describe how the quality considerations were scored or if they were reproducible. They state that meta-analysis (using statistical methods to combine data from different studies into a single summary measure of effect) was not an appropriate option because of the variations in preparations, methods, and outcomes measured. Even without meta-analysis, this is a good systematic review of the evidence for Echinacea for the prevention and treatment of URIs.

OUTCOMES MEASURED: The outcomes used in the treatment studies varied considerably. They included URI symptoms rated on a scale of 0 to 3, progression to a “real cold,” and the presence of influenzalike symptoms. Outcomes for the prevention trials included the time until the first URI and the severity of its symptoms.

RESULTS: The authors identified 13 blinded randomized trials. Nine of these studies were treatment trials, and 4 were studies of prevention. Eight of the 9 treatment trials reported a benefit. Six showed a statistically significant benefit, while 2 reported only a trend; the one study showing no benefit is unpublished and used insufficient doses of Echinacea. Data from one of the larger more methodologically sound studies¹ suggest that the number needed to treat to prevent a real cold among patients with the first sign of a cold was 5. Two of the prevention trials reported a marginal benefit: One initially reported a benefit but later reported no benefit, and one found no benefit. The major methodologic weaknesses identified included: lack of objective validated measures, no clear evidence that the treatment was indistinguishable from the placebo, and insufficient sample size.

CLINICAL QUESTION: Is Echinacea beneficial for the prevention or treatment of acute upper respiratory infections (URIs)?

BACKGROUND: Echinacea, taken for the prevention and treatment of URIs, is one of the most commonly used herbs. The goal of the authors of this study was to systematically review the randomized trials of Echinacea for the prevention or treatment of acute URIs.

POPULATION STUDIED: The authors reviewed the evidence from blinded placebo-controlled randomized trials of any formulation of Echinacea used for prevention or treatment of URIs. The study populations varied, and most were in Europe.

STUDY DESIGN AND VALIDITY: The authors identified studies by searching MEDLINE and other bibliographic reference services using variants on the term “Echinacea.” They also reviewed articles, books, and book chapters for references. They questioned herbal medicine experts in the United States and Germany about published and unpublished trials. Study quality was evaluated using the following criteria: randomization, blinding, power, validity, clinical relevance of outcome measurements, inclusion and exclusion criteria, indistinguishability between treatment and placebo, and appropriateness of conclusions. The authors went to great lengths to identify relevant studies, and it seems unlikely that any pertinent studies would have been missed. The authors do not describe how the quality considerations were scored or if they were reproducible. They state that meta-analysis (using statistical methods to combine data from different studies into a single summary measure of effect) was not an appropriate option because of the variations in preparations, methods, and outcomes measured. Even without meta-analysis, this is a good systematic review of the evidence for Echinacea for the prevention and treatment of URIs.

OUTCOMES MEASURED: The outcomes used in the treatment studies varied considerably. They included URI symptoms rated on a scale of 0 to 3, progression to a “real cold,” and the presence of influenzalike symptoms. Outcomes for the prevention trials included the time until the first URI and the severity of its symptoms.

RESULTS: The authors identified 13 blinded randomized trials. Nine of these studies were treatment trials, and 4 were studies of prevention. Eight of the 9 treatment trials reported a benefit. Six showed a statistically significant benefit, while 2 reported only a trend; the one study showing no benefit is unpublished and used insufficient doses of Echinacea. Data from one of the larger more methodologically sound studies¹ suggest that the number needed to treat to prevent a real cold among patients with the first sign of a cold was 5. Two of the prevention trials reported a marginal benefit: One initially reported a benefit but later reported no benefit, and one found no benefit. The major methodologic weaknesses identified included: lack of objective validated measures, no clear evidence that the treatment was indistinguishable from the placebo, and insufficient sample size.