Nolvadex (tamoxifen citrate) is very comparable to Clomid, behaves in the same manner in all tissues, and is a mixed estrogen agonist/antagonist of the same type as Clomid. The two molecules are also very similar in structure. It is not correct that Nolvadex reduces levels of estrogen: Rather, it blocks estrogen from estrogen receptors and, in those tissues where it is an antagonist, causes the receptor to do nothing.