Everything is toxic , what varies is the dosage, leaves are pretty safe, and can be taken as a tea daily if needed , the seeds on the other hand can easily be toxic if taken in the wrong amounts. just like any other medicine, taking the right amount is key. aspirin is safe, but not if you guzzle down a bottle of it.
graviola leaves I will use in my Flu buster tea, which usually has Graviola, Lemongrass, star anise , prunella vulgaris, bay-rum leaves, holy basil and lemon balm. all of which i have growing in my backyard with the exception of the Prunella which i get in Chinatown.