While I cannot comment on Cranberry...my vet and I have had a discussion in the regards to use of red raspberry leafs. She explained to me that the RRL causes hormonal changes. While it can help prepare the uterine horns for pregnancy...it can mess with contractions, milk production and more later on. If using RRL, wean your bitch off of them before they hit the 30 day mark. Use of RRL can cause abortions and early labor...but it can also cause the labor contractions to be uneffective, therefore sending your girl in for a c-section. As an FYI...Bitch pills contain RRL.