Nearly half of women using depot medroxyprogesterone acetate, commonly known as the birth control shot, will experience high bone mineral density loss in the hip or lower spine within two years of beginning the contraceptive, according to UTMB researchers Dr. Abbey Berenson and Dr. Mahbubur Rahman. The study, reported in the January 2010 issue of Obstetrics and Gynecology, was the first to show that women on DMPA who smoke, have low levels of calcium intake and never gave birth are at the highest risk for BMD loss.