These have worked a MIRACLE on my sensitive immune system. I was getting cold sores twice a month, which was an indication that my immune system was weakened. However, after taking these drops, I didn't get a cold sore for five months. Then after 5 months, I forgot to take the drops three days in a row and got another cold sore. I also work with kids and am exposed to a lot of their sicknesses and had never got sick until I started forgetting doses.