In the quest to discover why some people drink heavily while others don’t, researchers have found the answer may actually be quite simple: brain differences between the groups make alcohol consumption feel better to the heavier drinkers.

In a study with 25 people, about half of whom were heavy drinkers, brain scans found that alcohol triggered the release of endorphins in the nucleus accumbens and orbitofrontal cortex — areas of the brain that produce feelings of pleasure and reward — in all the study participants. The more endorphins released in the nucleus accumbens, the greater the feelings of pleasure reported by people in both groups.

But there was a key difference: among heavy drinkers, the more endorphins released in the orbitofrontal cortex, the greater the feelings of intoxication — something that didn’t happen among those in the group who were not heavy drinkers.

The findings show “that the brains of heavy or problem drinkers are changed in a way that makes them more likely to find alcohol pleasant, and may be a clue to how problem drinking develops in the first place,” said lead author Jennifer Mitchell, clinical project director at the Gallo Center and an adjunct assistant professor of neurology at the University of California, San Francisco.

“This is something that we’ve speculated about for 30 years, based on animal studies, but haven’t observed in humans until now,” she said. “It provides the first direct evidence of how alcohol makes people feel good.”

The next step, the authors said, is pinpointing the exact locations in the brain where endorphins are released, which could lead to the development of more effective drugs to treat alcoholism.

The study is published in the Jan. 11 issue of the journal Science Translational Medicine.