CHICAGO (AP) -- A big new study says obesity surgery may increase patients' chances for alcohol abuse.

Patients in the study who had gastric bypass surgery faced double the risk for excessive drinking two years later. That's compared with those who had a less drastic weight-loss operation.

Researchers think gastric bypass surgery changes how the body digests and metabolizes alcohol.

Only 11 percent of the bypass patients had drinking problems two years after the operation, but that was 50 percent more than before surgery. There was little change in patients who had other obesity operations.

The study involved nearly 2,000 patients from 10 centers nationwide. It was released online Monday in the Journal of the American Medical Association.