Marijuana use dampens brain's response to reward over time, U-M study finds

http://www.eurekalert.org/pub_releases/2016-07/uomh-mud070416.php

Public Release: 6-Jul-2016
Marijuana use dampens brain's response to reward over time, U-M study finds
Changes may increase risk of continued drug use and addiction
University of Michigan Health System

Most people would get a little 'rush' out of the idea that they're about to win some money. In fact, if you could look into their brain at that very moment, you'd see lots of activity in the part of the brain that responds to rewards.

But for people who've been using marijuana, that rush just isn't as big - and gets smaller over time, a new study finds.

And that dampened, blunted response may actually open marijuana users up to more risk of becoming addicted to that drug or others.

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"What we saw was that over time, marijuana use was associated with a lower response to a monetary reward," says senior author and U-M neuroscientist Mary Heitzeg, Ph.D. "This means that something that would be rewarding to most people was no longer rewarding to them, suggesting but not proving that their reward system has been 'hijacked' by the drug, and that they need the drug to feel reward -- or that their emotional response has been dampened."

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The new data on response to potentially winning money may also be further evidence that long-term marijuana use dampens a person's emotional response - something scientists call anhedonia.

"We are all born with an innate drive to engage in behaviors that feel rewarding and give us pleasure," says co-author Elisa Trucco, Ph.D., psychologist at the Center for Children and Families at Florida International University. "We now have convincing evidence that regular marijuana use impacts the brain's natural response to these rewards. In the long run, this is likely to put these individuals at risk for addiction."

Marijuana's reputation as a "safe" drug, and one that an increasing number of states are legalizing for small-scale recreational use, means that many young people are trying it - as many as a third of college-age people report using it in the past year.

But Heitzeg says that her team's findings, and work by other addiction researchers, has shown that it can cause effects including problems with emotional functioning, academic problems, and even structural brain changes. And, the earlier in life someone tries marijuana, the faster their transition to becoming dependent on the drug, or other substances.

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tags: drug use, drug abuse