Lasofoxifene, sold under the brand name Fablyn, is a nonsteroidal selective estrogen receptor modulator (SERM) which is marketed by Pfizer in Lithuania and Portugal for the prevention and treatment of osteoporosis and for the treatment of vaginal atrophy,[1][2] and the result of an exclusive research collaboration with Ligand Pharmaceuticals (LGND).

[5] In accordance, a network meta-analysis of SERMs for breast cancer prevention found the highest reduction in risk with lasofoxifene of all the drugs.

[3] Lasofoxifene has greatly improved oral bioavailability relative to tamoxifen and raloxifene, and this may also be involved in its greater potency.

[10] In September 2005, Pfizer received a non-approvable letter from the U.S. Food and Drug Administration regarding lasofoxifene (trade name Oporia), a selective estrogen receptor modulator for the prevention of osteoporosis.

[11] Lasofoxifene is under development by Sermonix Pharmaceuticals for the treatment of metastatic breast cancer and dyspareunia associated with vaginal atrophy in the United States and Europe.