Echinacea (E. angustifolia DC, E. pallida, E. purpurea) References
    
        
        
            
        
            Barrett B, Brown R, Rakel D, et al. Placebo effects and the common cold: a randomized controlled trial. Ann.Fam.Med 2011;9(4):312-322. 
  Bensch K, Tiralongo J, Schmidt K, et al. Investigations into the antiadhesive activity of herbal extracts... 
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