 The origin of the rumor is unknown; some believe it was started by a deliveryman for a competitor trying to cast aspersions based on prune juice's laxative effects, but it may simply be because many people feel that Dr Pepper tastes similar to prune juice.In 2009, an old ledger book filled with formulas and recipes was discovered by Bill Waters while shopping at antiques stores in the Texas Panhandle.Several sheets and letterheads hinted it had come from the W.B.