A new study found that a gene therapy used to treat Parkinson’s disease may cure alcoholism.

For the study, medical researchers turned eight rhesus macaque monkeys into heavy drinkers by offering them increasing amounts of alcohol, and then analyzed how a unique therapy reversed alcoholism in four of the subjects.

According to the New York Post, researchers offered free access to alcohol all day and within six months, the monkeys began binge drinking on a regular basis.

Kathleen Grant, a neuroscientist at Oregon Health & Science University (OHSU) and her colleagues set out to see if gene therapy already successful in Parkinson’s patients could be effective in treating the alcoholic monkeys. If it worked, it could open a new avenue of treatment for people with severe alcoholism.  

“We know we can get people with alcohol use disorder to stop drinking for short periods of time,” she told Wired. “But the desire to drink again often supersedes medication.” Grant, and a group of researchers tried a different approach ─ resetting the brain’s dopamine pathway to change reward signals.

They injected a gene that makes the GDNF (glial-derived neurotrophic factor) protein, that in previous studies stimulated the production of dopamine, into four of the alcoholic animals. After making two small incisions on either side of each monkey’s skull, they injected genetically engineered viruses that contained the GDNF cells into a bundle of neurons near the brainstem, called the ventral tegmental area. Neurons in that area are involved in making dopamine, the “feel good” hormone, and distributing it throughout the brain.

When the experiment began, the macaques were voluntarily downing the equivalent of a human drinking about nine drinks a day. After injecting the gene therapy, the researchers initiated an imposed abstinence period of eight weeks for the monkeys and then allowed them to resume drinking alcohol for four weeks. They offered water alongside the alcohol, says Wired. This pattern was repeated for a year, alternating four weeks of abstinence with four weeks of drinking alcohol.

Amazingly, when alcohol was introduced the first time after therapy, the monkeys who received the procedure decreased their drinking by half compared to the control group. In subsequent exposures to alcohol the monkeys who were treated drank even less. By the end of the year, the treated monkeys consumed 90% less alcohol than their control counterparts.

“This was incredibly effective,” said Grant, who is chief of the Division of Neuroscience at OHSU’s Oregon Primate National Research Center, in a news release. “Drinking went down almost to zero. For months on end, these animals would choose to drink water and just avoid drinking alcohol altogether. They decreased their drinking to the point that was so low we didn’t record a blood-alcohol level.”

Grant explained that while acute alcohol use boosts dopamine production, chronic drinking decreases the amount of this pleasurable chemical released in the brain.

“Dopamine is involved in reinforcement of behavior, and in people finding certain things pleasurable,” Grant said. “Acute alcohol use can increase dopamine. However, drinking it chronically, the brain adapts in such a way that it decreases the release of dopamine. So, when people are addicted to alcohol, they don’t really feel more pleasure in drinking. It seems they’re drinking more because they feel a need to maintain an intoxicated state.”

Grant says that the monkeys who were treated with the gene therapy protocol permanently started overexpressing dopamine as they decreased their drinking dramatically. The study was published the journal Nature Medicine.

Alcohol use disorder and deaths related to alcohol pose a significant problem in the United States and around the world, with an estimated 140,000 deaths annually from alcohol-related causes, according to the National Institute on Alcohol Abuse and Alcoholism. The new study involves treatment that permanently and irreversibly alters part of the brain, and while it isn’t ready for human trials, may raise both medical and ethical issues, says the Post.

“It would be most appropriate for people who have already shown that all our normal therapeutic approaches would not work for them,’ said Grant. “They are likely to create severe harm or kill themselves due to their drinking. It would be a last resort if all other treatment options fail.”