Is there any interaction between tamoxin and graviola?

No one knows: Graviola has not been studied in humans, so what happens when taken with tamoxifen is not known. There is evidence from mouse experiments that it may help with breast cancer by downregulating epidermal growth factor, however, very little is known about it's effect in humans. There is some concern that it may cause a Parkinson's like syndrome. I'd stay away from this until more is know about it.