I have been taking the #1 for one for a couple of years and have no problem taking it on an empty stomach right before bed even, I think it is the pepper, and if you have any tolerance built up to it I don't see the harm in trying it once to see? Just my two cents though. What is this Master cleanse ya'll are talking about? The liver cleanse? I'm a little lost. :) Ya'll have a good week, Caitlin Lorraine