Why the mostly commonly performed bariatric surgery in the U.S. doubles patients' risk for drinking problems, compared with a less severe weight-loss procedure

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Gastric bypass surgery for weight loss doubles the risk of alcohol problems two years later, compared with bariatric surgery using the banding technique, according to new research published in the Journal of the American Medical Association.

The study of nearly 2,000 patients at 10 American hospitals was the first to directly examine the risk for alcohol use disorders before and after different types of obesity surgery, including Roux-en-Y gastric bypass, the most commonly performed weight-loss surgery in the U.S. The procedure involves stapling off most of the stomach and rerouting food directly to a lower part of the intestine, making eating large meals difficult and uncomfortable, and limiting the amount of calories absorbed.

Gastric bypass seems to increase patients’ risk of alcohol problems by making the body more sensitive to lower doses of booze: it allows more alcohol to get to the bloodstream faster because it skips most of the stomach and is better absorbed by the intestines. Addiction research shows that the faster a drug hits, and the greater its intensity, the more addictive it tends to be. (This is why snorting or injecting prescription painkillers or stimulants is more addictive than taking them orally.)

Two years after gastric bypass, about 9.1% of gastric bypass patients had developed drinking problems — up significantly from before the procedure — the study found, compared with about 5.6% of patients who had drinking problems two years after stomach-banding surgery. The latter procedure involves putting an inflatable band around the stomach to reduce the amount of food it can hold; while it limits the amount of food that can enter the stomach, it still requires food to pass through the entire system and therefore doesn’t affect the way alcohol is absorbed.

The findings confirm an earlier study, which examined the medical records of people who had these surgeries and looked for alcoholism-related hospitalizations afterward.

(MORE: Bypassing Obesity for Alcoholism: Why Some Weight-Loss Surgeries Increase Alcohol Risk)

Although gastric bypass did double the risk for alcohol problems, compared with banding surgery, the overall change in rates of alcohol disorders before and after surgery was small. Before any kind of weight-loss surgery, about 7.6% of the patients in the study had some type of alcohol problem — including frequent binge drinking, boozing in the morning, or blacking out while drinking — with 2.8% showing symptoms of alcoholism. After surgery, 9.6% had an alcohol problem and a full 5.5% had alcoholism symptoms.

The authors note that although this increase may seem small, with 70% of obesity surgeries using the gastric bypass technique and with more and more people seeking surgery as rates of obesity rise, it means that 2,000 additional Americans each year may be likely to develop alcohol problems.

Notably, the study indicates that weight-loss surgery itself doesn’t necessarily raise the risk of alcohol problems. People who had banding surgery, for example, did not have more drinking problems after surgery, suggesting that people don’t substitute the pleasure of large meals with large doses of drink.

There was also no association between the amount of weight lost and the risk of alcohol problems. If there had been such a connection, it might have revealed people’s desire for addictive escape: for example, people who lose a lot of weight might be happy and therefore uninterested in drinking, while those who don’t slim down might use alcohol to drown out their sorrow. The few studies looking directly at this issue have had conflicting results so more research is needed to understand the risk.

(MORE: Diet Psych Out: Why ‘Health’ Food Is Less Satisfying, Even If It’s Sinful)

As in previous studies of substance use disorders, the research found that being younger was independently associated with greater risk for alcohol problems after surgery. The vast majority of addictions develop among people in their 20s — if people haven’t had an alcohol or drug problem by that time, the odds of developing one are greatly decreased.

The study also found that having an alcohol problem in the year before surgery increased the risk of having one afterward, unsurprisingly; however, it didn’t look at lifetime history of substance problems, so it couldn’t tell definitively whether people were developing new drinking problems or relapsing back into old ones. Also confirming previous findings, it showed that being male, having less social support and using recreational drugs increased the risk for alcohol disorders after surgery.

The authors write: “[I]t is concerning that 1 in 8 participants reported consuming at least 3 drinks per typical drinking day and 1 in 6 participants reported consumption at a hazardous level in the second postoperative year. … Regardless of alcohol history, patients should be educated about the potential effects of bariatric surgery, particularly [gastric bypass] to increase the risk of [alcohol problems].”

Maia Szalavitz is a health writer for TIME.com. Find her on Twitter at @maiasz. You can also continue the discussion on TIME Healthland‘s Facebook page and on Twitter at @TIMEHealthland.