People who drink heavily were encouraged to think about consuming alcohol and given an intravenous shot of the party drug.
Researchers at University College London said the participants subsequently had less of an urge to drink over time.
Dr Ravi Das, the study’s lead author, said the research aimed to explore how memories associating alcohol with reward can lead to addiction.
He explained: “Learning is at the heart of why people become addicted to drugs or alcohol. Essentially, the drug hijacks the brain’s in-built reward-learning system, so that you end up associating environmental ‘triggers’ with the drug. These produce an exaggerated desire to take the drug.”
Dr Das added that, once “reward memories” are created, it is hard to re-learn healthier associations.
Ninety people who drank heavily and preferred beer took part in the study.
Those taking part did not have a formal diagnosis of alcoholism and had not sought treatment. On average, they were drinking 74 units of alcohol per week – or about 30 pints of beer.
The participants were given a glass of beer and told they would be able to drink it after finishing a task.
They were asked to rate how strongly they wanted to drink it and were asked to rate their anticipated pleasure, which the researchers say activates the reward memories surrounding beer drinking.
On the first day they were allowed the beer, but on the second day the beer was unexpectedly removed.
By taking the beer away, the researchers removed the anticipated reward, which disrupts the reward memory.
On this second day, one third of the participants were given an intravenous infusion of ketamine after the beer was removed, another third were given a placebo, and the final third were given ketamine but had not done the drinking memory retrieval task.
Normally, when the reward memory is disrupted, the brain acts to re-stabilise and store the memory.
However, the researchers suggest ketamine prevents this memory re-storage process by blocking a receptor in the brain.
Over a 10-day follow-up, the people who were given ketamine combined with memory retrieval showed significant reductions in their urge to drink. They also drank less alcohol and on fewer days than the others.
They were also given a small sample of beer, but had less urge to drink it, enjoyed it less and had less desire to continue drinking than the others.
The effect was sustained over a nine-month follow-up, with the main group improving more than the other two by halving their average weekly alcohol consumption over the nine months.
All three groups were found to have decreased their drinking to different levels, but only the two groups given ketamine showed a statistically significant reduction in drinking volume.
“We found that heavy drinkers experienced a long-term improvement after a very quick and simple experimental treatment,” said Dr Das.
The study, which was experimental and not a clinical trial, was published in Nature Communications.