The genus Echinacea belongs to the family Compositae, commonly referred to as the sunflower family. Of the known species, E. purpurea, E. angustifolia, and E. pallida are commonly used in herbal medicine. Extracts derived from the root and aerial parts are widely used in Europe and the United States as nonspecific immunostimulants and to prevent or treat the common cold and influenza. However, natural products differ greatly in composition ⁽²⁶⁾, mainly due to the use of different species, variable plant materials or extraction methods, and the addition of other components. Preclinical studies suggest immunostimulatory and anti-inflammatory effects ⁽²⁷⁾. A standardized echinacea preparation inactivated influenza viruses ⁽²⁸⁾ and may improve respiratory activity ^(2) (3). In animal models, echinacea stimulated erythropoiesis, increased blood-oxygen transport ^(29) (30), produced anxiolytic effects ⁽³¹⁾, and exhibited wound-healing properties ^{(32) (33) (34)}.

Clinical data indicate that echinacea is ineffective in preventing the common cold caused by rhinoviruses ⁽⁴⁾ or in treating upper respiratory infections ^{(5) (6) (16)} but positive findings were reported with higher doses ⁽⁷⁰⁾. Studies of its ability to reduce incidence and duration of the common cold yielded mixed results ^{(7) (8) (9) (10) (22) (35) (36)}. Other analyses do not indicate any benefits for treating colds, and weak evidence for a prophylactic benefit ^(26) (37), but a large randomized trial found an echinacea formulation to be as effective as oseltamivir for influenza, and with fewer adverse events in the echinacea group ⁽³⁸⁾. In a review of 17 clinical trials involving 3,363 participants, echinacea supplements were found to affect reductions in pro-inflammatory cytokines that play a role in the progression of cytokine storm and acute respiratory distress syndrome (ARDS) ⁽⁶⁸⁾. Echinacea was also reported useful in preventing respiratory tract infections and reducing associated antibiotic usage in children ⁽⁷¹⁾.
Small studies have shown that a standardized echinacea root extract has immunomodulating activity ⁽³⁹⁾; an echinacea/sage spray was useful in treating acute sore throats ⁽¹⁷⁾; and a formula containing dry root extracts of Echinacea purpurea and Echinacea angustifolia may be useful as an adjuvant therapy for decreasing relapse incidence in patients treated for genital condylomatosis ⁽⁶⁷⁾ and in those with cervical low-grade squamous intraepithelial lesions ⁽⁷²⁾. Data on anxiolytic effects are mixed ^(69) (73) but findings on improving or enhancing athletic performance are mixed ^(40) (41). A topical echinacea extract was reported effective in alleviating symptoms associated with atopic eczema ⁽⁶³⁾. Echinacea may also have anticancer potential evidenced by the cytotoxic effects exerted by an extract and a major compound, cichoric acid, in human colon cancer cells ⁽⁴²⁾.

Some studies suggest that echinacea could decrease plasma levels, affect therapeutic efficacy, or cause adverse effects with some anticancer drugs ^(25) (43). In HIV-infected patients, co-administration with etravirine was found to be safe and well tolerated ⁽⁴⁴⁾. In a large population-based study, use of echinacea was associated with a slight increase in diastolic blood pressure ⁽⁴⁵⁾. There is insufficient evidence regarding the efficacy and safety of echinacea during pregnancy ⁽⁴⁶⁾.