Well, it may have an effect on the release of histamine from the mast cells, but I don't believe that it blocks any of the histamine receptors or helps more histamine to be broken down. The histamine that causes my son's symptoms isn't coming from his mast cells, but from bacteria in his gut, so it isn't having a direct effect on the histamine. I believe that it is making it so that less of the histidine in the food is available for the bacteria to make histamine with and I hope that it is killing the bacteria, too, but that will probably take a while.