Since then, several well-designed studies have found that echinacea is no better than placebo for the treatment of Upper Respiratory Infection:
A randomized, double-blind, placebo-controlled trial compared dried, encapsulated unrefined Echinacea purpurea and angustifolia with placebo in 148 college students who had at least two cold symptoms for less than 36 hours [18]. There was no significant difference in the mean duration of cold symptoms (6.27 versus 5.75 days in the echinacea and placebo groups, respectively). No treatment effect could be demonstrated after controlling for a number of variables such as symptom duration prior to enrollment and use of non study medications and there was no difference in the severity of cold symptoms.
A randomized trial in 407 children ages 2 to 11 with 707 URI episodes treated patients at the onset of URI symptoms with either dried pressed Echinacea purpurea juice of the above-ground herb harvested at flowering or placebo [19]. Treatment was continued until resolution of the URI or a maximum of 10 days. Compared with placebo, echinacea did not reduce duration of symptoms (9 versus 9 days), days of fever (0.81 versus 0.64 days), number of days of peak severity (1.60 versus 1.64 days), severity of URI symptoms, peak severity of symptoms, or parental assessment of severity. Overall, adverse events were similar in the two groups, but a significantly higher percentage of patients treated with echinacea developed a rash (7.1 versus 2.7 percent).
A randomized trial compared three times daily treatment with Echinacea purpurea 100 mg (freeze-dried pressed juice from the aerial portion of the plant) or placebo in 128 adults [20]. Treatment was started within 24 hours of the onset of cold symptoms and continued until resolution of symptoms or for a maximum of 14 days. There were no significant differences in symptom scores or in time to resolution of symptoms.
A randomized trial examined the effects of three different preparations of Echinacea angustifolia root (extracted with supercritical carbon dioxide, 60 percent ethanol, or 20 percent ethanol) and placebo in 399 volunteers who were challenged with rhinovirus [21]. Treatment was administered three times daily with a 1.5 mL tincture (the active preparation contained the equivalent of 300 mg of echinacea root). None of the preparations had an effect significantly different from placebo on mean total symptom score or on the measured weight of nasal secretions.
Whether other formulation or dosages of echinacea may be effective is unknown.
Prevention ? Well-designed studies of echinacea have not generally found it to be efficacious for the prevention of community-acquired URI:
A randomized, controlled trial of 109 patients with a history of more than three colds or respiratory infections in the preceding year, randomly assigned the study subjects to receive 4 mL fluid extract of Echinacea purpurea or 4 mL of placebo juice twice daily [22]. The incidence and severity of colds and respiratory infections were determined during eight weeks of follow-up, based upon patient reported symptoms together with findings on physical examination. During the eight-week treatment period, 35 of 54 patients (65 percent) in the echinacea group and 40 of 54 patients (74 percent) in the placebo group had at least one cold or respiratory infection (relative risk 0.88, 95% CI 0.60-1.22). The average number of colds and respiratory infections per patient was 0.78 in the echinacea group and 0.93 in the placebo group (difference 0.15, CI -0.12-0.41). The median duration of colds and respiratory infections was 4.5 days in the echinacea group and 6.5 days in the placebo group (difference 2 days, CI -1-+3 days). There were no significant differences between treatment groups in the number of infections in each category of severity. Side effects were observed in 11 patients (20 percent) of the echinacea group and in 7 patients (13 percent) of the placebo group (p = 0.44).
In one study, 302 adults were randomized in a double-blind fashion to E. purpurea, E. angustifolia, or placebo for 12 weeks [4]. The time until onset of the first URI was not significantly different for the three groups (66, 69, and 65 days, respectively). There were also no significant differences in URI rates for the two echinacea groups compared to placebo.
Experimental studies have also generally not found that echinacea is effective in preventing URI after challenge with rhinovirus [21,23,24]:
One trial randomly assigned 48 adults to receive echinacea (2.5 mL three times daily) or placebo for seven days before and seven days after nasal inoculation with rhinovirus type 39 [24]. There was a similar rate of microbiological infection with rhinovirus in both groups (92 versus 95 percent). There was a trend toward fewer patients treated with echinacea developing clinical colds (58 versus 82 percent, p = 0.11) [4].
A randomized trial examined the effects of three different preparations of Echinacea angustifolia root (extracted with supercritical carbon dioxide, 60 percent ethanol, or 20 percent ethanol) and placebo in 399 volunteers who were challenged with rhinovirus [21]. Treatment was administered three times daily with a 1.5 mL tincture (the active preparation contained the equivalent of 300 mg of echinacea root) for five days prior to rhinovirus challenge. Rates of infection and clinical URI were not significantly different for any of the preparations or placebo.