Hi Bugsy. I just did some research about pepsin and my understanding so far is that improper use of it may cause stomach ulcer. :( So I am not sure it can be used alone safely during a fast or semi-fast on an empty stomach. But o-p-e is another matter, I think; as allantoin and E3 in it are all tissue repairers, they might be there to do some patch-up for damages caused by friendly fire from pepsin (just my guess and I am no biochemist). So letís just see how well it turns for you. And of course, if I find any other useful information, Iíll be sure to let you know.