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Echinacea for the Prevention and Treatment of the Common Cold

Complementary and Alternative Therapies Evidence-based Summary


Date of review: October 2004

A cold is a mild viral infection affecting the upper respiratory tract. Echinacea is a plant often used in herbal medicine for the management of colds. This evidence summary identified three systematic reviews, four narrative reviews and 26 clinical trials (with a total of 5,588 patients) on the use of Echinacea for the prevention and treatment of the common cold. Trial results are difficult to compare as different strength Echinacea preparations have been tested, Echinacea extracts varied in quality, different species of Echinacea have been used, different parts of the plant have been tested, and in some preparations other plant extracts or homeopathic components were added.

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Results summary


There is insufficient information from the identified studies to conclude that Echinacea is effective for the prevention of the common cold. However, there is some evidence that Echinacea can reduce the severity and duration of symptoms associated with a cold. Mild but reversible side effects have been reported with the use of Echinacea, including indigestion, headache, and dizziness. More serious side effects have also been reported including hepatitis, asthma and severe allergic reaction (anaphylaxis).


Background


Common cold


The common cold is a mild, self-limiting viral infection of the upper respiratory tract.1 Colds are most common in young children, who usually experience 5-7 colds a year. Adults usually experience 2-3 colds a year, but may experience more if they live with or frequently encounter young children.2 The signs and symptoms of the common cold appear one to three days after infection, and last for a few days (and usually not longer than two weeks). A sore throat tends to be the first symptom to appear, followed by a runny nose (rhinitis), sneezing, nasal congestion, and cough. Headache and blocked sinuses (sinusitis) may also be experienced due to inflammation and congestion of the nasal passages and sinuses. Earache is a common complication of colds, particularly in children. Often the symptoms of a cold can mimic those of the flu (influenza).

Echinacea


Echinacea is a distinctive perennial (lasting throughout the year) plant, with erect, hairy, spotted, stems growing up to a metre in height. Flower heads look like daisies, with purple-rayed florets and a dark brown central cone. The leaves are hairy, the lower leaves oval to lance-shaped and coarsely and irregularly toothed.3 Echinacea is also referred to as American coneflower, black Sampson hedgehog, Indian head, snakeroot, red sunflower, scurvy root,4 and black Susan.5 In New Zealand Echinacea is the most common medicinal herb commercially grown,6 and has become one of the most popular herbal remedies on the US and European markets, with three different species used for medicinal purposes.4, 7 E. purpurea is the best known of the many species of Echinacea, however extracts and whole plant products made from E. purpurea (purple cone flower),8 E. angustifolia (narrow-leaved cone flower) and E. pallida (pale-flowered Echinacea) are the most common species used in herbal medicine.9Laboratory studies show that Echinacea extracts contain compounds that have anti-inflammatory and anti-viral properties.10

Echinacea can be obtained as an “over the counter” product from health food shops, supermarkets, pharmacies, etc. A medical herbalist may also prescribe Echinacea. The practice of herbal medicine is not currently regulated by legislation in New Zealand, however many herbal medicine practitioners are affiliated with a self-regulated professional body (such as the New Zealand Association of Medical Herbalists).


Evidence reviewed in this summary


Efficacy information


  • Systematic Reviews: Two systematic reviews on the use of Echinacea for the common cold,11, 12 and one systematic review on the immune-enhancing properties of Echinacea13 were identified for this evidence summary. The first review was conducted by the Cochrane Acute Respiratory Infections Group and was last updated on the 18th July 2001.11 This review included 16 randomised and quasi-randomised trials (eight prevention trials and eight treatment trials).14-29 The second review12 identified 13 randomised trials (four prevention trials and nine treatment trials including an unpublished manuscript30), published between 1981 and 1999. 14, 17, 21-32 All trials were double-blinded and 11 of the trials14, 17, 21-29 were also included in the Cochrane review. The third review identified 26 trials published between 1961-1992 on the immune enhancing properties of Echinacea.13 Only 12 of the 26 trials were on the use of Echinacea for the prevention and treatment of upper respiratory infection (six prevention trials and six treatment trials). All 12 trials were also included in the previous reviews. In addition to the three systematic reviews identified for this evidence summary, three structured reviews with narrative reporting of the results,5, 33, 34 and one critical review of the medicinal properties of Echinacea9 were also identified.
  • Clinical Trials: The above three systematic reviews identified 19 clinical trials14-32 on this topic, which included between 32 and 1,255 people – a total of 4,047 participants. One trial was unpublished30. Since these reviews were conducted, an additional six treatment trials7, 35-39 (with a total of 1,424 participants), and one prevention trial40 (with 117 participants) have been published. At least one clinical trial (expected to involve 720 people) on the use of Echinacea for the common cold is currently underway see (http://www.controlled-trials.com).
  • Case control studies/Cohort studies/Case studies: Given the extensive coverage of the above systematic reviews, no case-control, cohort or case studies were assessed for this evidence summary3

Safety information


  • Systematic reviews: Two of the above systematic reviews11, 12 reported information on side effects associated with the use of Echinacea for the common cold, as did the three structured reviews with narrative reporting5, 33, 34 and the critical review of the medicinal properties of Echinacea.9
  • Clinical trials: Further information on the safety of Echinacea was also reported by the six treatment trials not included in the above systematic reviews.7, 35-39
  • Other studies: A narrative review was also identified on abnormal laboratory test results and the toxic effects of herbal medicines.41 The review included side effects associated with the general use of Echinacea. Given the comprehensive information provided by the above studies, no further information on side effects was sought.


Evidence on efficacy


Prevention of the common cold


Information on the use of Echinacea for the prevention of the common cold is available from nine clinical trials17-23, 32, 40 representing 1,349 participants aged between 10-84 years. Four of the trials17, 21-23 were included in two of the systematic reviews.11, 12 The review authors stated that trial results were difficult to compare as different strength Echinacea preparations had been tested, Echinacea extracts varied in quality, different species of Echinacea had been used, different parts of the plant had been tested, and in some preparations other plant extracts or homeopathic components were added. As a result of differences in trial design, variation in the product being tested and the relatively small number of people involved in some trials (two trials involved less than 200 people),17, 23 the authors concluded that there was insufficient evidence to support the use of Echinacea or recommend a specific Echinacea preparation for the prevention of the common cold.11, 12 Results from the trial not included in the above reviews failed to find a significant relationship between Echinacea and the prevention of symptoms associated with the common cold.40

Treatment of the common cold


Information on the use of Echinacea for the treatment of the common cold is available from 17 clinical trials7, 14-16, 24-31, 35-39 representing 4,239 participants aged between 2-71 years. Results from the systematic review12 and the critical review9 that summarised the findings from 15 of these trials14-16, 24-31, 36-39 concluded that compared to placebo:

  • Echinacea reduced the severity of symptoms associated with a cold by 10%-50%. Results varied according to the study population, the type of Echinacea preparation, and the dose of Echinacea used.9, 25, 37
  • Echinacea reduced the duration of symptoms associated with a cold by one15 to three days39. However, this finding is based on results from two trials which were limited by small sample size (3215-8039 participants), and inadequate reporting of measures related to duration of symptoms.9
  • The duration of symptoms associated with a cold is reduced more if Echinacea is taken when cold symptoms first appear, rather than once symptoms are well established. 4 However, this finding is based on results from two trials limited both in size (9538 - 12024 participants) and methodological quality.9
  • Echinacea preparations vary widely in composition and are often found in combination with other potentially active constituents, which makes it difficult to determine what dose of Echinacea to use.12
In contrast to these findings, results from two recently published trials that were not included in the above reviews found that Echinacea had no detectable effect on the duration or severity of the common cold in adults35 or children (aged 2 - 11 years).7


Evidence on safety


Findings from the two systematic reviews11, 12, the three narrative reviews5, 33, 34, one critical review9, and six additional treatment trials7, 35-39 reviewed for this summary, indicate that:

  • Side effects associated with the use of Echinacea for the common cold tend to be mild and reversible, and include mild indigestion (dyspepsia), headache, and dizziness,5 as well as gastrointestinal upset (diarrhoea, constipation) and skin rash.34
  • In one trial involving 524 children, a rash was experienced in 7.1% of those treated with Echinacea compared to 2.7% of those treated with placebo.7
  • Serious side effects (such as allergic reactions involving anaphylaxis) associated with the use of Echinacea for the common cold have been reported, but are rare12. For example, in one trial involving 524 children, two children receiving Echinacea were hospitalised after the sudden onset of severe stridor7 (the harsh sound heard on inhalation caused by air passing through a constricted passage – a symptom often associated with anaphylaxis).42
  • Allergic reactions to Echinacea can occur in people who are sensitive to plants in the daisy family (e.g. sunflower seeds, feverfew, chamomile or ragweed).5, 33, 34
In terms of side effects associated with the use of Echinacea in general, the Australian Adverse Drug Reaction Advisory Committee received 11 reports of adverse reactions between July 1996 and September 1997.41 Of these 11 reports, three were for hepatitis, three were for asthma; one report was of a rash, muscle pain (myalgia), and nausea; and one report was of a severe allergic reaction (anaphylaxis).


Cited references


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