CHICAGO (AP) ― The most common type of obesity surgery may increase patients’ chances for alcohol abuse, according to the largest study to demonstrate a potential link.

Patients who had gastric bypass surgery faced double the risk for excessive drinking, compared with those who had a less drastic weight-loss operation.

Gastric bypass surgery shrinks the stomach’s size and attaches it to a lower portion of the intestine. That limits food intake and the body’s ability to absorb calories. Researchers believe it also changes how the body digests and metabolizes alcohol; some people who’ve had the surgery say they feel alcohol’s effects much more quickly, after drinking less, than before the operation. The study suggests that may lead to problem drinking.

The researchers asked nearly 2,000 women and men who had various kinds of obesity surgery at 10 centers nationwide about their drinking habits one year before their operations, versus one and two years afterward. Most didn’t drink excessively before or after surgery, and increases in drinking didn’t occur until two years post-surgery.

More than two-thirds had gastric bypass surgery and were most at risk. Two years after the surgery, almost 11 percent, or 103 of 996 bypass patients, had drinking problems, a 50 percent increase from before surgery.

By contrast, about 5 percent of patients who had stomach-banding obesity surgery drank excessively two years later, similar to the pre-surgery numbers. Too few patients had other types of weight-loss surgery to make strong comparisons.

The study was released online Monday in the Journal of the American Medical Association.

About 8 percent of U.S. adults abuse alcohol by drinking excessively. The study authors say their results suggest that an additional 2,000 people each year will develop drinking problems because of obesity surgery.

More than 200,000 stomach-reducing surgeries are performed each year. Gastric bypass, also called stomach-stapling, is the most common and generally results in more weight loss than other methods. The benefits of gastric bypass surgery include sometimes reducing diabetes and heart disease risks.

Patients should be screened for alcohol problems before and after surgery and told about the risks, said lead author Wendy King, an assistant professor at the University of Pittsburgh’s graduate school of public health.

Dr. Robin Blackstone, president of the American Society for Metabolic and Bariatric Surgery, said the results echo findings in smaller studies and clearly show an alcohol-related risk from gastric bypass surgery.

“We in the medical community are going to take that seriously,” said Blackstone, an obesity surgeon in Scottsdale, Arizona. The findings are being presented at the medical group’s meeting in San Diego this week.

She noted that obese people are often socially isolated because of their weight, and that drinking often increases when patients have slimmed down and pursue a more active social life. Blackstone said she and many other doctors routinely warn patients that they may be more sensitive to alcohol, and that the study reinforces that advice.

Patients seeking obesity surgery often undergo psychological evaluations to make sure they are stable enough to handle the operation and life changes afterward. Guidelines recommend against the surgery for people with substance abuse problems including excessive drinking, said psychologist Leslie Heinberg, director of behavioral services for Cleveland Clinic’s bariatric and metabolic institute.

Study results were based on patients’ responses on questionnaires about alcohol use.

Problems included frequently having at least three drinks or at least six drinks on one occasion; needing to drink in the morning; and forgetting events because of alcohol use.

Two years after surgery, these problems were more common in gastric bypass patients, and in men, young adults and smokers after either type of surgery.

Stomach banding involves surgically putting an adjustable band around the stomach to decrease the amount of food it can hold. It is reversible but less common than gastric bypass in the United States.