Schwarz E, Metzler J, Diedrich JP, Freudenstein J, Bode C, Bode JC (2002). "Oral administration of freshly expressed juice of Echinacea purpurea herbs fail to stimulate the nonspecific immune response in healthy young men: results of a double-blind, placebo-controlled crossover study". J. Immunother. 25 (5): 413–20. doi:10.1097/00002371-200209000-00005. PMID12218779. S2CID23051179.
Yale SH, Liu K (June 2004). "Echinacea purpurea therapy for the treatment of the common cold: a randomized, double-blind, placebo-controlled clinical trial". Arch. Intern. Med. 164 (11): 1237–41. doi:10.1001/archinte.164.11.1237. PMID15197051.
Schwarz E, Metzler J, Diedrich JP, Freudenstein J, Bode C, Bode JC (2002). "Oral administration of freshly expressed juice of Echinacea purpurea herbs fail to stimulate the nonspecific immune response in healthy young men: results of a double-blind, placebo-controlled crossover study". J. Immunother. 25 (5): 413–20. doi:10.1097/00002371-200209000-00005. PMID12218779. S2CID23051179.
Yale SH, Liu K (June 2004). "Echinacea purpurea therapy for the treatment of the common cold: a randomized, double-blind, placebo-controlled clinical trial". Arch. Intern. Med. 164 (11): 1237–41. doi:10.1001/archinte.164.11.1237. PMID15197051.
Schwarz E, Metzler J, Diedrich JP, Freudenstein J, Bode C, Bode JC (2002). "Oral administration of freshly expressed juice of Echinacea purpurea herbs fail to stimulate the nonspecific immune response in healthy young men: results of a double-blind, placebo-controlled crossover study". J. Immunother. 25 (5): 413–20. doi:10.1097/00002371-200209000-00005. PMID12218779. S2CID23051179.