A study done to compare the benefits and risks of two different drugs used to treat invasive breast cancer found both effective, but with slightly differing side effects. Researchers conducted a trial at nearly 200 clinical centers across the country. The women chosen for the trial were at an increased risk for breast cancer. The 19,747 postmenopausal women in the study were either given tamoxifen or raloxifene for five years. At the end of the study, tamoxifen and raloxifene seem to offer the same level of benefit in breast cancer prevention. The group of women on tamoxifen had slightly more uterine cancer diagnosis and lung or deep vein blood clots than the group of women on raloxifene, but not in significant numbers.

However, tamoxifen is seen by primary care physicians as a toxic chemoprevention drug, where raloxifene is seen as a fairly safe drug. Raloxifene is currently prescribed for the prevention and treatment of osteoporosis in postmenopausal women. According to the researchers, "This trial confirms the previously reported benefit of raloxifene in reducing the risk of invasive breast cancer and indicates that raloxifene is as active as tamoxifen in this regard. If raloxifene is approved by the Food and Drug Administration for the prevention of breast cancer, primary care physicians may be more willing, given their experience with raloxifene, to prescribe it for breast cancer chemoprevention than they have been to prescribe tamoxifen."