January 12th, 2012
05:29 PM ET
If you like to drink but want to stop and don't seem to have to willpower to do so, it may be because chemicals in your brain are telling you to order another pint, new research suggests.
It's been long thought that alcohol triggers the release of naturally occurring opioids in the brain's reward centers, but research has documented how this process works only in animals. A new study in the journal Science Translational Medicine offers insights into why alcohol can be so addictive in humans.
Researchers used positron emission tomography (PET) to look at the distribution of chemicals in the brains of volunteers. Participants were 13 "heavy social drinkers" and 12 healthy control subjects. Women considered "heavy social drinkers" usually consume 10 to 16 drinks per week, and heavy-drinking men typically have 14 to 20 drinks per week. Those in the control group drink fewer than five drinks per week among women, and seven drinks per week among men.
It seems that some people experience this opioid release differently. Researchers found a correlation between how good volunteers felt after drinking and the amount of opioid released. In the heavy drinkers, a single drink leads to the release of more opioid in the orbital frontal cortex and the nucleus accumbens - two regions that play a role in reward.
In other words, some people's brains give them more of an opioid release when they drink, leading them to perceive alcohol as more pleasurable than other people do. And the orbital frontal cortex makes them subconsciously learn to want that rush of pleasure again - making them seek and crave alcohol in a way they're not even aware of.
"If you’re getting some reinforcement or reward from something, like alcohol or other kinds of abusable drugs, at that level your brain is telling you this is something important to you," said Michael Owens, a neuropharmacologist at Emory University who was not involved in the study.
That means if you're an alcoholic and consciously want to stop drinking, it's hard to stop because part of your brain has learned that drinking is important and compels you to continue.
"It’s something you have to fight to not partake in again," he said.
It's important to note, however, that this study did not involve alcoholics. Many of the "heavy drinkers" in this study would have on average two drinks a day, which isn't necessarily going to lead to dependency.
Owens said the results of this study were not surprising, but it was good that the hypothesis about how alcohol works in the brain was confirmed by science.
The researchers' ultimate objective is to come up with new ways of treating alcohol addiction, said Jennifer Mitchell, adjunct assistant professor at University of California, San Francisco and lead author of the study.
Currently, the main drug available to help addicts stay off alcohol and drugs that is approved by the U.S. Food and Drug Administration is naltrexone. This drug binds to the same receptors in the brain that opioids would bind to, so the opioids don't have anywhere to go. "When you do drink, the alcohol gives you less of a reward," Mitchell explains. "You feel less good than you would otherwise."
But few doctors prescribe naltrexone, partly because of the side effects, Mitchell says. Headaches, nausea, irritability and achiness can result from this medication, which would drive people away from it, especially if they're already in withdrawal and trying not to drink.
This new research gives ammunition to justify looking for alternatives to naltrexone, Owens said. Still, making a drug that acts in the brain with fewer side effects is tricky, even if you try to isolate specific brain regions, he said. Brain regions that perform different functions have similar biochemistry, so it's hard to affect some without also touching upon others.
The next step in this line of inquiry is to look at the role that other opioid receptors play, Mitchell said, and then determine which receptors a drug should affect in order to get the benefits without the side effects.
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