Nearly one in three drugs has a postmarket safety event, according to a study published earlier this month in JAMA. The study looked at 222 novel therapies approved between 2001 and 2010. We spoke to Nicholas Downing, clinical fellow in the Department of Medicine at Brigham and Women's Hospital and lead author of the study, about the findings, the limits of clinical trials, and whether the U.S. Food and Drug Administration needs to do more to improve surveillance of drugs once they are approved.