A new study provides clues about the brain mechanisms that drive people to abuse alcohol. The study found a link between how good people feel after they drink, and the amount of endorphins—proteins with opiate-like effects—released in their brain.

Similar findings have been seen in animal studies, but this is the first time they have been observed in humans, according to a news release by the University of California, San Francisco, where the research was conducted. “This is something that we’ve speculated about for 30 years, based on animal studies, but haven’t observed in humans until now,” said lead author Jennifer Mitchell, PhD. “It provides the first direct evidence of how alcohol makes people feel good.”

Researchers studied 15 volunteers; 13 were heavy social drinkers and 12 were not. Women were considered heavy social drinkers if they consumed 10 to 16 drinks a week, while men in that category had 14 to 20 drinks weekly, CNN reports. Women who were not heavy social drinkers had fewer than five drinks a week, while the men had fewer than seven drinks.

The subjects’ brains were scanned using positron emission tomography (PET) to examine the distribution of chemicals produced in response to drinking. In heavy drinkers, just one drink led to the release of more endorphins in two brain regions that play a role in pleasure and reward. They perceived drinking as more pleasurable than the non-heavy drinkers. That feeling leads them to crave alcohol, the researchers said.

They noted that the study, which located the precise areas of the brain where endorphins are released, may provide a possible target for the development of better treatments for alcohol abuse.

The findings appear in the journal Science Translational Medicine.