P & B Shakes taken in prune juice..

I have been doing a p & b shake in the morning in any juice handy, and have had good results. I have not modified my diet as of yet, I am however watching calorie intake. I have had the unfortunate "running out of juice" problem because my kids will not stay out of my juice when theirs is gone. I decided they most definately will not pilfer prune juice. My question after that unnessesary explanation is: What do I have to look forward to? Will the prune juice cause any unpleasant effects?