Would you like to be able to double the amount of alcohol that enters into your bloodstream when you drink? Let’s say you consume the equivalent of two standard drinks containing one ounce of alcohol. Your blood alcohol level (BAL) would double and you would likely exceed the legal driving limits in thirty minutes. Oh, and you would feel drunker as well. Does this sound crazy? Yet that is exactly what happens to someone who has had gastric bypass surgery.

A recent 2015 study, “Effect of Roux-en-Y Gastric Bypass Surgery,” published in JAMA Surgery evaluated the physical and subjective effects of ingested alcohol on individuals who had received a common from of gastric bypass surgery called Roux-en-Y gastric bypass. The find is from a small study of 8 obese women who had undergone the surgery and 9 obese women who had not yet had the surgery. All the women consumed the equivalent of two standard alcoholic drinks or two placebo nonalcoholic drinks in two 10-minute drinking sessions.

HealthDay reported that the researchers measured the blood alcohol concentration (BAC) levels of the participants. “Drunkenness” was measured by matching each participant’s behavior to an “Addiction Research Center Inventory.” BAC levels rose much faster in the bypass group and peaked at levels twice those seen in the non-bypass group. The BAC levels of the bypass group also exceeded legal driving limits for thirty minutes after consuming their second drink. “BAC levels never exceeded legal driving limits among the non-bypass group.”

Feelings of drunkenness were also greater in the bypass group. Using criteria developed by the U.S. National Institute on Alcohol Abuse and Alcoholism, the researchers concluded that just two drinks were the equivalent of a binge-drinking episode with the potential risk of an alcohol use disorder. Dr. Samuel Klein, one of the study’s authors, said:

This surgery literally doubles the amount of alcohol that immediately enters your bloodstream. . . . And it also increases the patient’s long-term risk for alcoholism, because the risk for a binge episode of drinking goes up. And we know that binge drinking increases the risk for going on to develop alcoholism in the future.

Although Klein and his team used a more rigorous methodology than had been used before, the study’s finding isn’t new. Dr. John Morton, chief of bariatric and minimally invasive surgery at the Stanford University School of Medicine, said this was a well-known phenomenon.  “It’s about physiology,” he said. There is an increased sensitivity to alcohol because the surgery removes alcohol receptors in the stomach. These receptors are also found in the liver. “And if you bypass and remove a portion of either of these, you have a change in blood alcohol levels.”

ScienceLine reported on a woman who lost 180 pounds within a year of her gastric bypass surgery in 2009. She started ordering wine in place of dessert at dinner so she wouldn’t sit there ‘”twiddling my fork” while others ate their dessert. The occasional glass of wine became more often and she spent the next two years fighting an alcohol use disorder. She began drinking at home alone, two bottles of wine per occasion. She began hiding bottles from her husband, driving while drunk and blacking out when drinking. She discovered injuries she didn’t remember getting.

A 2012 study, “Prevalence of Alcohol Use Disorders Before and After Bariatric Surgery,” found that while alcohol use disorder (AUD) symptoms were not significantly different one year after the surgery, they were significantly higher in the second postoperative year. The presence of an AUD in the year before surgery substantially increased the odds of an AUD in the first two postoperative years. “Regular alcohol consumption prior to surgery also independently increased the likelihood of postoperative AUD.” One in 8 participants reported consuming at least three drinks per typical drinking day; and 1 in 6 participant said they drank at a hazardous level in the second postoperative year.

A 2013 Swedish study, “Alcohol Consumption and Alcohol Problems After Bariatric Surgery” did a long-term follow up of over 2,00 obese patients who had three types of bariatric surgery: vertical banded gastroplasty (VBG), banding and gastric bypass. The follow up time of the study ranged from 8 to 22 years. Alcohol consumption standards established by the World Health Organization (WHO) were used to assess the risk levels of alcohol consumption during the follow up period.

During the follow up time, 93.1% of the surgery patients and 96.0% of the controls reported alcohol consumption classified as low risk by the WHO. However, in comparison to the control group, the gastric bypass group had an increased risk of alcohol abuse diagnoses, alcohol consumption at least at the WHO medium risk level, and related alcohol problems. VBG also increased the risk of these conditions, while banding was not different from controls.

Another 2013 study, “Substance Use Following Bariatric Weight Loss Surgery,” looked at the course of substance use (alcohol, cigarettes, recreational drugs, and composite substance use), as measured by the Compulsive Behaviors Questionnaire. Participants completed questionnaires preoperatively and 1,3, 6, 12 and 24 months after surgery. There were no significant changes in participant’s reported frequencies of cigarette smoking or recreational drug use. However, there was a significant increase in alcohol use for participants who had undergone RYGB surgery, the same Roux-en-Y gastric bypass as reported above in the 2015 study by .

Because patients have a reduced tolerance for alcohol after RYGB surgery, they may experience the rewarding aspects of alcohol use sooner and more frequently, which may contribute to the increase in frequency of alcohol use after LRYGB surgery.

Steph Yin for ScienceLine noted that many patients are unaware of the risk of an alcohol use disorder when they get gastric bypass surgery. And scientists aren’t clear themselves on why the risk exists. An early theory was that of addiction transfer. People adopt new addictions after weight-loss surgery because they can no longer fulfill their food addictions. However, evidence like that above in “Effect of Roux-en-Y Gastric Bypass Surgery” suggests there may be an anatomical explanation. Namely that metabolic and hormonal changes triggered by gastric bypass leave patients particularly vulnerable to alcohol use disorders. It’s possible, said Yin, that both are right. Or maybe it’s something else entirely. We just don’t know at this point.

According to James Mitchell, a doctor and professor of neuroscience at the University of North Dakota, “Whether it’s addiction transfer or something else going on, we really don’t know at this point.” What is certain is that the high rates of alcohol use disorders in postoperative gastric bypass patients cannot be attributed to chance.