I have been taking this for over 1.5 years and have not had a cold since I started. I suffered from 3-4 bad colds per year (talking colds that knock you out for an entire weekend or make a work week miserable).
I rarely write reviews on Amazon. But I started taking this product before an international flight in the middle of winter, after which I would spend several days in a crowded house of friends. I truly expected to immediately get sick as often happens for me with travel or staying in crowded spaces. Shocked! Not sick. Another international flight and busy travel schedule, no sickness.
Got through a cold and flu season unscathed, another flight, not sick. All summer. Now back into cold and flu season; dinner with friends and family complaining of colds, shaking hands with clients sniffling and coughing in my office. Still not sick. About to fly on another international trip-- flying with confidence! This product works amazingly well. I am so pleased. I take it as often as I can remember, two capsules at a time. On average, end up taking it every other day, and works super well! Highly recommended!