While a meta-analysis shows that probiotics reduce the duration of the common cold by an average of 1.89 days, Lactobacillus plantarum HEAL9 and Lactobacillus paracasei 8700:2 team up to reduce the duration of the common cold by as much as 2.4 days in one study. This research review covers mechanisms of action in multiple clinical trials as well as four double-blind randomized clinical trials on the common cold using 1 billion colony-forming units of this probiotic combination.