Lasofoxifene is among the most potent SERMs reported in protection against bone loss and cholesterol reduction. The excellent oral potency of lasofoxifene has been attributed to reduced intestinal glucuronidation of the phenol. Unlike raloxifene, lasofoxifene satisfies the requirement of a pharmacophore model that predicts resistance to gut wall glucuronidation. The structural requirement is a non-planar topology with the steric bulk close to the plane of a fused bicyclic aromatic system. The interactions between the ER and lasofoxifene are consistent with the general features of SERM-ER recognition. Lasofoxifenes large flexible side chain terminates in a pyrrolidine head group and threads its way out toward the surface of the protein, where it interferes directly with the positioning of the AF-2 helix. A salt bridge forms between lasofoxifene and Asp-351. The charge neutralization in this region ER may explain some antiestrogenic effects exerted by lasofoxifene.