The major side effect of
arimidex is a screwed up lipid profile. This can of course lead to cardiovascular disease. Even in low doses, adex screws up your lipids. You should get your cholesterol checked regularly on
arimidex. Arimidex also upregulates the estrogen receptors. This means that when you stop taking it, not only do you have more estrogen receptors, but you are also more sensitive to the effects of estrogen.
Nolvadex, I believe, is tougher on the liver than arimidex & you run the risk of blood clots & the development of certain types of cancer, amongst several other things.