Echinacea Echinacea, or coneflower, is a native North American wild-flower that is a member of the Asteraceae family. Of the nine known Echinacea species, three are favored for medicinal purposes:
E. purpurea, E. angustifolia, and E.
pallida. Uses and Benefits: Echinacea is commonly marketed to help treat or prevent colds, flu, and other mild upper respiratory infection (URI)-like illnesses. The plant was traditionally used by Native Americans to treat infections and wounds, and as a general cure-all. Although popular in the 19th and early 20th centuries, echinacea's use declined greatly in the U.S. after the introduction of antibiotics. It was introduced in Germany in the early 1900s, where in recent years it has been avidly researched and promoted as an immune system stimulant to help the body fight infections.
Pharmacology:Alkylamides, caffeic acid derivatives (e.g., echinacosides and chicoric acid derivatives), and polysaccharides are the best-studied constituents. The polysaccharides may not be in finished products and may not be absorbed orally to a significant extent. Concentrations of individual components vary between different species and plant parts (e.g., roots vs. above-ground portions).
Clinical Trials:Two high-quality, systematic reviews of the worldwide literature have evaluated echinacea for preventing or lreating the common cold or viral-type URls. Focusing on double-blind, randomized, controlled trials (RCTs), both found published European studies (primarily from Germany) that met crileria for inclusion. Almost identical trials were included in both reviews, and individual trial sizes ranged from 95 to 646 subjects. A variety of different echinacea preparations were studied, including extracts from all three species and different plant parts (roots vs. above-ground portions); seven of the studies utilized echinacea mono-preparations (not combined with other herbs). Although reported to be randomized and double-blind, many trials contain potential biases such as lack of objective validated measures, inadequate descriptions of methods, and lack of intention to treat analysis. The results of both systematic reviews were similar.
Acute Treatment of URis-In the eight European trials that evaluated echinacea for acute treatment of URis (four trials used echinacea mono-preparations), almost every study demonstrated beneficial results for the echinacea product compared to placebo. These trials found that echinacea reduced the signs or symptoms or shortened the duration of a viral URI-like illness when initiated in the first few days of symptoms and continued for 8-10 days. Benefits compared to placebo were modest, but were statistically significant in all studies. In addition, a recent U.S. double-blind RCT of an echinacea tea product found similar symptomatic improvements on a simple three-question form given to the 95 subjects 14 days after starting therapy (P < 0.001 ).12 One unpublished Canadian trial of an E.
angustifolia product failed to find any benefits compared to placebo, and other trials with negative results are known to have not been published.
Prevention of URis-Four large European trials (three using echinacea mono-preparations) conducted over 2-3 months for prevention of illness found positive trends, but no statistically significant benefits compared to placebo.9-11 A recent experimental prophylaxis trial also found no statistically significant benefits for a U.S. echinacea Product. 13 In this double-blind trial, 117 adults were given echinacea or placebo for 2 weeks and then challenged with rhinovirus culture. Again, positive trends were found in the echinacea group, but no statistically significant differences compared to placebo were demonstrated for infection rate (by viral culture and antibody response), development of clinical colds, or individual cold symptoms.
Other Uses-Many other European clinical trials have reported beneficial effects for other infectious disorders (e.g., pertussis, recurrent candida infections), malignancies, and in the reduction of undesirable effects of anti-neoplastic therapy. However, most of these studies contain significant methodologic weaknesses, and reported benefits are not convincing. For the prophylaxis of recurrent genital herpes, a recent double-blind RCT of an
E. purpurea product found no significant benefit compared to placebo.
Adverse Effects:Echinacea preparations are very well tolerated. In the clinical trials, side effects were similar to those seen in the placebo groups. No adverse effects have been reported with oral Products other than rare allergic reactions and a single case of recurrent erythema nodosum.
Side Effects and Interactions: In an
in vitro study, echinacea inhibited activity of the isozyme of cytochrome P450, a common drug-metabolizing enzyme. This has not been validated
in vivo, and there are no documented drug interactions reported for echinacea.
Cautions: People with allergies to plants of the Asteraceae family (e.g., daisy, sunflower, chrysanthemum, ragweed) may be allergic to echinacea as well. Echinacea is considered to be a mild immunostimulant; the German Commission E discouraged its use in patients with immune disorders such as AIDS, systemic lupus, and multiple sclerosis, and for chronic use longer than 8 weeks. However, this notion that echinacea may worsen immune-mediated diseases is controversial. Adverse effects in these populations have not been reported, and research does not necessarily support these Iimitations. 20 In fact, in a 12-week phase 1 study in 14 HIV-positive patients, 1000 mg t.i.d. of
E. angustifolia was associated with reduction in viral loads by 0.32 log-10 (p < 0.05).21 CD4 counts did not change significantly, and there were no toxic or adverse events.
Based on the evidence to date, it would be prudent to monitor patients with immune disorders or those taking immunosupressant more closely, and to avoid echinacea in high-risk populations (for example, transplant patients). But note that adverse effects and absolute contraindications remain theoretical.
Although generally best avoided by pregnant and breast-feeding women due to limited data, a prospective cohort study of 207 women using echinacea products during pregnancy found no increased ased risk for malformations or other adverse pregnancy outcomes.
Preparations & Doses:Dosing recommendations are confounded by a wide variety of preparations using different species, plant parts, and extracts. Unlike other herbal medicines researched in Germany, there are no standardized preparations. Extracts of 1-5 g or more of dried herb per day have been traditionally recommended by herbalists, typically divided t.i.d.
Of the European products found effective for acute URI symptoms in clinical trials, three are distributed in the U.S. under the "rand names EchinaGuard (by Nature's Way), Echinaforce (by Bioforce), and Esberitox (by Enzymatic Therapy; also contains white cedar and wild indigo). All contain different extracts and have very different dosing regimens. Most of the other preparations used in the European clinical trials are ethanolic extracts of E.
purpurea or E.
pallida. They were dosed at 2-4 droppersful (about 2-4 ml) daily, equivalent to about 900 mg/day of the crude herb.
The tea product found effective in the U.S. trial, Echinacea Plus (Traditional Medicinals, Inc.), contains the equivalent of 1275 mg of dried echinacea (from all three species) per tea bag.
Summary Evaluation: The available evidence supports a modest benefit for the treatment of acute URI symptoms, although publication bias and potential methodologic flaws tempers interpretation of the published trials. Nevertheless, based on the overall evidence, the herb's relative safety, the relatively benign nature of the illness, and lack of other proven therapies, echinacea is a reasonable therapeutic option for the symptomatic treatment of acute viral URis. Echinacea has minimal or no benefits for prophylaxis of URis, and other indications have not been adequately evaluated.
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