No, it only prevents conversion of certain hormones into estrogen, it won't block estrogen that's already been formed through other pathways. Personally I like just a few weeks of nolva as that's always been good enough for me. However I seem to recover very easily no matter the dosage, cycle length, or gear used, so use a combo. Aromatase inhibitor, estrogen blocker, possibly HCG as well, or one of those OTC products that seem to work well too. But I wouldn't use just straight aromasin.