In a syndicated editorial penned by Dr. Mehmet Oz (who is known best for "The Dr. Oz Show") and Dr. Mike Roizen (chief medical officer at the Cleveland Clinic Wellness Institute), the good doctors proclaim that "It's official (again)- violent video games hurt teens." They determine (without citation) that playing games like Call of Duty: Black Ops (which they say features dismembered limbs, obscene language, torture) and Hitman: Absolution is "bad for teens" (both games are rated "M" and therefore shouldn't be played by teens).
They also say that "violent games harm young, developing brains by fueling aggressive behavior, dulling empathy and causing sleep problems."
At least they offer some good advice for parents on limiting screen time and using the ESRB's ratings system before buying children games that are outside of the proper classification for age groups. They also recommend joining your kids in physical activities that reduce stress and improves impulse control.
Of course the problem with all these proclamations from Dr. Oz and his colleague is that he is not qualified to make them. He holds no degrees in clinical psychology or therapy, and has never conducted any research on the affects of violent video games. Dr. Oz is a Professor of Surgery, and Vice-Chairman - Department of Surgery at Columbia University College of Physicians & Surgeons in NYC; and Columbia University College of Physicians and Surgeons, New York, NY an attending surgeon at New York-Presbyterian Hospital/Columbia University Medical Center.
You can read the editorial here.