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− |