MedicalResearch.com Interview with:
Mary P. Heitzeg, PhD
Department of Psychiatry
University of Michigan
MedicalResearch.com: What is the background for this study? What are the main findings?
Response: We wanted to find out if marijuana use changed the way the brain’s reward system responded to natural rewards. To probe response to natural reward, we used the chance to win some money and we observed brain response using functional magnetic resonance imaging (fMRI). We looked at brain activity when participants were 20 years old on average, and then again 2 years later and 4 years later. We found that over time marijuana use was associated with a decrease in the brain’s reward response to the chance to win money. This finding is consistent with current theories of addiction that suggest that repeated use of a substance may dampen the brain’s reward response to things normally perceived as pleasurable and this alteration may drive the individual to continue substance use.
MedicalResearch.com: What should readers take away from your report?
Response: This study provides evidence that marijuana use impacts the brain’s response to natural rewards such that they may not seem as pleasurable. This may put individuals at risk for addiction. For recreational users, the findings challenge the perception that marijuana is a “safe”’ drug and that there is little risk to the individual in using marijuana. Furthermore, this evidence can be used by physicians and patients in making decisions about medical marijuana use on a case-by-case basis.
MedicalResearch.com: What recommendations do you have for future research as a result of this study?
Response: The participants in this study were late in their adolescence or young adults. Because marijuana is the most used illicit drug among teenagers, it is important to track brain functioning beginning prior to the teen years and follow them through young adulthood to fully understand the impact that marijuana use has on the developing brain. It will also be important to understand whether different forms of marijuana use – e.g., edibles, vaporized, smoked – all have similar effects.
MedicalResearch.com: Is there anything else you would like to add?
Response: This is the first study to look at the impact of marijuana on the brain’s reward system using multiple measurements of brain activation over time.
MedicalResearch.com: Thank you for your contribution to the MedicalResearch.com community.
Martz ME, Trucco EM, Cope LM, et al. Association of Marijuana Use With Blunted Nucleus Accumbens Response to Reward Anticipation. JAMA Psychiatry. Published online July 06, 2016. doi:10.1001/jamapsychiatry.2016.1161.
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