Prescription drugs are known to include a number of potential side effects. We now know what that number is. Researchers from the Regenstrief Institute and the Indiana University School of Medicine found an average of 70 reactions per drug, a number that can overwhelm physicians trying to select suitable treatments for their patients. In the study, appearing in the May 23, 2011 issue of the Archives of Internal Medicine, the researchers also found that more commonly prescribed drugs averaged around 100 side effects. The upper range was as many as 525 reactions. The study involved analysis of more than 5,600 drug labels and more than half a million labeled effects.