Drug Profile

Background

The term echinacea, when used in the context of dietary supplements, denotes one or more of three echinacea species: E. purpurea, E. angustifolia and E. pallida. Various echinacea preparations may contain one or more of these (the first two are most common), and the supplement may be derived from the roots, herbs or whole plant. The chemical content of the extract varies by the season in which it is harvested and by the method of extraction. Some potentially active compounds have been isolated, but effectiveness has never been confirmed.

The plant is a member of the daisy family and is native to North America, where Native Americans have used it since the 1600s for snakebites, wounds, tonsillitis, headache and cold symptoms.[1],[2] In the early 1900s, attention turned to use for infection, but it was eclipsed by the advent of antibiotics. In Germany, where it is marketed as a prescription drug, the supplement attracted attention as both a preventive and treatment for the common cold, and it is widely used.

Claimed uses

In 1998, a study that reviewed all previous randomized, controlled trials of echinacea was published.[3] The review found some positive evidence for the effectiveness of echinacea in the prevention and treatment of the common cold but acknowledged that “few recommendations can be made regarding the use of Echinacea products in practice. The heterogeneity of the available preparations and the limited quality and consistency of the evidence do not allow clear conclusions about which product might be effective in what dose and in what circumstances.” Of the 16 highly regarded studies in the review, all but two were conducted in Germany, and only one was published in the large medical journal database MedLine.[4]

Since that time, a number of better-designed trials have been conducted. Below, Public Citizen summarizes the data from those trials and the earlier MedLine-published trial.

Preventing the common cold

We identified three randomized, placebo-controlled studies of echinacea. One used an extract of E. purpurea, another an extract of E. purpurea and E. angustifolia and the third did not specify. Two of the studies showed no benefit of echinacea upon the time to the first cold, the percentage that had a single cold, or the number of colds.[5],[4] In a third trial, patients were randomized to echinacea or placebo and then exposed to a cold virus. The rate of clinical infections was similar between the two groups.[6]

Treating the common cold

Two of the prevention trials also measured the impact of echinacea upon the course of the common cold. Four treatment-only trials were also identified. Of these six studies, three evaluated a preparation with all three echinacea species and two used a formulation with only E. purpurea and E. angustifolia. The sixth study was an experimental study[5] (see "Preventing the Common Cold" section) and did not specify which forms of echinacea were studied.

The four larger, best-conducted studies, published in the best medical journals, all found no statistically significant impact of echinacea on the duration or severity of cold symptoms.[7],[5],[6] These included the experiment and the two most recently published studies, one of which involves children.[8] Two of the smaller studies did claim beneficial effects, but these studies were of poor quality. In one, which claimed the duration of a cold could be reduced by a median of three days, the study subjects in the two groups appear to have been different at the beginning of the study,[9] raising questions about whether the randomization was adequate. In the second, a very crude questionnaire evaluated the duration and severity of symptoms.[2] In addition, it is unclear that the patients in this study were properly blinded to the taste of the echinacea herbal tea that was studied.

In 2002, the authoritative Medical Letter on Drugs and Therapeutics reviewed the data on echinacea for both the prevention and treatment of the common cold and concluded that “there is no convincing evidence that echinacea decreases the severity or shortens the duration of an upper respiratory infection.”[10]

The results of a randomized controlled trial conducted to investigate if echinacea was effective or provided any benefits in treating the common cold were published in the Annals of Internal Medicine in December 2010. Patients either received no pills, placebo pills (blinded) or echinacea pills (blinded or open label). The results found that in this trial echinacea did not have a “statistically significant” effect on the course of the common cold. Any beneficial effect of echinacea observed in the trial was not large and did not have a major effect on changing the course of the common cold.[11]

Preventing and treating recurrent genital herpes

There is only one published randomized, placebo-controlled trial, and despite a less-than-ideal follow-up of the enrolled patients, it shows no effectiveness for echinacea in reducing either the frequency or severity of genital herpes recurrences.[12] Use of the supplement for herpes prevention or treatment seems particularly unjustified, given the existence of effective therapies for that condition.

Interactions with other drugs

No interactions with other drugs have been reported, but this has not been studied formally. Because use of echinacea is intended to stimulate the immune system, some researchers suggest avoiding the use of echinacea if the patient is taking immunosuppressive drugs.[13],[1]

Side effects

The most common adverse effects appear to be bad taste, stomach upset, headache and dizziness.[13] In one randomized study, there was a statistically significant increase in rashes among echinacea-treated patients,[8] but this has not been reported in other randomized trials. Allergic reactions to echinacea, some leading to anaphylaxis, a life-threatening reaction, have been reported.[14] Some observers caution against echinacea use for longer than eight weeks or in patients with systemic progressive illnesses such as HIV infection, tuberculosis or multiple sclerosis.[15] A study of echinacea use during pregnancy reports that the rate of major birth defects was not increased, but there were only enough patients in the study to detect a tripling or more in such defects.[16]

In August 2012, the Medicines and Healthcare products Regulatory Agency in the U.K. (MHRA) issued information to the public that oral products containing echinacea should not be given to children younger than 12 years of age. This warning was due to reports of a low risk of rare allergic reactions that may be severe in this age group. The advisory stated that based on available information, the potential risks associated with using echinacea-containing products in children younger than 12 years old do not outweigh the perceived benefits of using these products.[17]

Summary

There is no convincing evidence that echinacea reduces the frequency or severity of the common cold or recurrent genital herpes.