Hi Sam
This is Kathy from BCNA's Policy Team. We always recommend to women that they talk to their doctors, especially their medical oncologist, about any vitamin supplements or other natural therapies they are thinking of using. There is evidence that high doses of Vitamin C can reduce the effectiveness of chemotherapy, including for breast cancer. This would be why your doctors have recommended against having Vitamin C infusions. Other supplements, such as St John's Wort, can also make chemotherapy less effective.
There is really good, reliable information about interactions between herbs, vitamin supplements including Vitamin C and other products on the Memorial Sloane Kettering Cancer Centre's Herbs website. There is also an app you can download to your phone.
Hope this helps.
Kathy
