Echinacea “can prevent colds”, reports The Daily Telegraph, while the Daily Mail reports that the “largest ever clinical study into Echinacea finds herbal remedy can protect against colds”.
These headlines were based on a study which found that giving healthy adults three doses of the herbal remedy Echinacea daily for four months reduced the combined number and duration of cold episodes by an average of 26% compared to placebo.
What was not widely reported in the news was that the study also reported finding no significant difference between the groups when they looked at the number of colds each group caught. So, the difference seems to have been related to how long a cold lasted, rather than the frequency of cold.
This randomised control trial was well designed and had a good sample size (755 participants), however, there are a number of oddities in the reporting of the study findings that cast a shadow of doubt over the results, such as:
• no declaration of funding and only partial disclosure of conflict of interests
• no results table
• limited reporting of unpleasant side effects
• no estimates of error around the results reported
• selective reporting of results
• the applicability of the results to the general population
The prior plausibility for echinacea as a cold remedy is very low, but not zero. As an herbal product it can feasibly have biological activity. The claim that it “boosts the immune system” is not credible, as such a phenomenon is not generally accepted. Basic science research essentially finds that the immune system is activated by echinacea, but this has not been distinguished from a non-specific immune response to a foreign substance. In other words, stimulating the immune system non-specifically (I can do this by punching you in the arm) and “boosting” the immune system so that it functions more effectively against an infection, are not the same thing. Leaping to the latter conclusion is not justified by the evidence.
See this for a rundown of prior studies – Belief in Echinacea
Is Echinacea effective for preventing and treating the common cold or is it just a placebo? My interpretation of the evidence is that Echinacea does little or nothing for the common cold. Initial reports were favorable, but were followed by four highly credible negative trials in major medical journals. A Cochrane systematic review was typically wishy-washy. The Natural Medicines Comprehensive Database rates it as only “possibly effective”…
If it worked so great, the results would be more obvious than wishy-washy.
Tip: Molly Hogdgon