Hi @jumper123 Checking with a drug interaction site online there were no negative interactions listed between Cytoxan and Vitamin D3 (cholecalciferol)

However, even though Vit D3 is a very common over the counter supplement, it isn’t without side effects if someone takes too much, especially if your levels are already in the normal range. So the best person to ask about whether this is a good supplement for you would be your doctor. Have you had your Vit D levels checked recently?