Echinacea is most often used to enhance immune function in individuals who have colds and other respiratory tract infections. Two reviews have assessed the efficacy of echinacea for this primary indication. A review by the Cochrane Collaboration involved 24 randomized, double-blind trials with 33 comparisons of echinacea mono-preparations, which are single-ingredient echinacea preparations, and placebo. Trials were included if they involved echinacea for cold treatment or prevention, where the primary efficacy outcome was cold incidence in prevention trials and duration of symptoms in treatment trials. Overall, the review did not find significant evidence of benefit for echinacea (among all species) in treating colds. Preparations made from the aerial parts of E purpurea plants and prepared as alcoholic extracts or pressed juices were discussed as possibly being preferred to other formulations for cold treatment in adults, but still having a weak overall treatment effect. In prevention trials, pooling results suggested a small relative risk reduction of 10–20%, but no statistically significant benefit within individual trials.
A separate meta-analysis involving 14 randomized, placebo-controlled trials of echinacea for cold treatment or prevention was published in Lancet. In this review, echinacea decreased the risk of developing clear signs and symptoms of a cold by 58% and decreased symptom duration by 1.25 days. This review, however, was confounded by the inclusion of four clinical trials involving multi-ingredient echinacea preparations, as well as three studies using rhinovirus inoculation versus natural cold development.
Echinacea has been used investigationally to enhance hematologic recovery following chemotherapy. It has also been used as an adjunct in the treatment of urinary tract and vaginal fungal infections. These indications require further research before they can be accepted in clinical practice. E purpurea is ineffective in treating recurrent genital herpes.
Adverse effects with oral commercial formulations are minimal and most often include unpleasant taste, gastrointestinal upset, or allergic reactions (eg, rash). In one large clinical trial, pediatric patients using an oral echinacea product were significantly more likely to develop a rash than those taking placebo. In a small Norwegian mother and child cohort study, 0.5% of women reported taking any formulation of echinacea during early-stage (conception up to pregnancy week 17) or late-stage pregnancy and had no adverse pregnancy outcomes compared to pregnant women who did not use echinacea. Herbal supplements, and particularly those made from alcoholic extracts, should only be used in pregnancy and lactation after consultation with the primary health care provider.
Until the role of echinacea in immune modulation is better defined, this agent should be avoided in patients with immune deficiency disorders (eg, AIDS, cancer) or autoimmune disorders (eg, multiple sclerosis, rheumatoid arthritis). Although there are no well-documented herb-drug interactions for echinacea, in theory, it should also be avoided in persons taking immunosuppressant medications (eg, organ transplant recipients). Co-administration of an echinacea product containing E purpurea and E angustifolia root had no effect on warfarin pharmacodynamics, platelet aggregation, or baseline clotting in healthy subjects. Human studies have shown no effect of varied E purpurea preparations on the pharmacokinetics of lopinavir, ritonavir, etravirine, and darunavir.
It is recommended to follow the dosing on the package label, as there may be variations in dose based on the procedure used in product manufacture. Standardized preparations made from the aerial parts of E purpurea (Echinaforce, Echinaguard) as an alcoholic extract or fresh pressed juice may be preferred in adults for common cold treatment if taken within the first 24 hours of cold symptoms. It should not be used on a continuous basis for longer than 10–14 days.