Echinacea for the prevention and treatment of upper respiratory tract infections: A systematic review and meta-analysis

Background: Echinacea preparations are commonly used to prevent and treat upper respiratory tract infection.

Objectives: To assess current evidence for the safety and efficacy of echinacea containing preparations in preventing and treating upper respiratory tract infection.

Data sources: MEDLINE, EMBASE, CAB extracts, Web of Science, Cochrane DARE, clinicaltrials.gov and the WHO ICTRP - 1980 to present day.

Eligibility criteria: Randomised double-blind placebo-controlled trials using an echinacea preparation to prevent or treat upper respiratory tract infections.

Participants and interventions: Participants who are otherwise healthy of any age and sex. We considered any echinacea containing preparation.

Study appraisal and synthesis methods: We used the Cochrane collaborations tool for quality assessment of included studies and performed three meta-analyses; on the prevention, duration and safety of echinacea.

Results: For the prevention of upper respiratory tract infection using echinacea we found a risk ratio of 0.78 [95% CI 0.68-0.88], for the treatment of upper respiratory tract infection using echinacea we found a mean difference in average duration of -0.45 [95% 1.85-0.94] days, finally for the safety meta-analyses we found a risk ratio of 1.09 [95% CI 0.95-1.25].

Limitations: The limitations of our review include the clinical heterogeneity - for example many different preparations were tested, the risk of selective reporting, deviations from our protocol and lack of contact with study authors.

Conclusions: Our review presents evidence that echinacea might have a preventative effect on the incidence of upper respiratory tract infections but whether this effect is clinically meaningful is debatable. We did not find any evidence for an effect on the duration of upper respiratory tract infections. Regarding the safety of echinacea no risk is apparent in the short term at least. The strength of these conclusions is limited by the risk of selective reporting and methodological heterogeneity.

Implications of key findings: Based on the results of this review users of echinacea can be assured that echinacea preparations are safe to consume in the short term however they should not be confident that commercially available remedies are likely to shorten the duration or effectively prevent URTI. Researchers interested in the potential preventative effects of echinacea identified in this study should aim to increase the methodological strength of any further trials.

Prospero id: CRD42018090783.