Reference	Objective	Design	Evidence
Douglas et al. [494]	Vitamin C against common cold	MA	1A−
Barrett et al. [495]	Ecchinacea for common cold	RCT	2A−
McElhaney et al. [496]	Extract of the roots of North American ginseng (Panax quinquefolium)	RCT	2A+
Heimer et al. [497]	Vitamin C to prevent common cold	MA	1B−