For GSK, already facing more than 800 lawsuits in the United States filed on behalf of children who were born with congenital heart defects as a result of exposure to Paxil in the first trimester, more bad news came this week. Researchers in Canada in a study published by the British Medical Journal warned that Paxil, an antidepressant commonly prescribed to women with breast cancer, can lessen or even nullify the effects of the breast-cancer drug tamoxifen, increasing a woman's risk of death.

According to the authors, the study exposes an "extremely common" and potentially life-threatening drug interaction that is "widely underappreciated," yet entirely avoidable.

Breast cancer is the most commonly diagnosed cancer in women worldwide. National Cancer Institute, a component of the National Institutes of Health, estimates that, based on current rates, 12.7 percent of women born today will be diagnosed with breast cancer at some time in their lives.