Study: Marijuana affects brain’s reward center

Evan Carter
The Detroit News

A new study put out by University of Michigan researchers suggests that over time, marijuana use dampens the response of the area of the brain that responds to rewards.

Researchers with UM’s Addiction Research Center and Department of Psychology found over time marijuana use shifts the brain’s reward system so that a person may need more of the substance to get that level of satifaction they would normally get from “natural rewards,” such as food.

“This kind of suggests that marijuana may be biasing the brain’s reward system away from things the brain would normally find pleasurable,” said the study’s Senior Researcher and UM Assistant Professor Mary Heitzeg.

According to Heitzeg, when a person smokes marijuana, THC passes from the lungs into the bloodstream, which carries the THC to the brain and other organs. In the brain, THC acts on specific brain cell receptors that ordinarily react to natural THC-like chemicals. One effect of THC in the brain is a release of dopamine from an area of the midbrain called the ventral tegmental area to the nucleus accumbens, which is a brain structure involved in motivational processes.

The study involved 108 young adults who are at high risk for substance use disorder, self-reporting on their marijuana use once a year and received 3 MRI brain scans over a 4 year period. According to the reports submitted by study participants, some involved did not use marijuana, while others used it in light, moderate, or heavy amounts.

Researchers were particularly interested in marijuana’s effect on the brain’s mechanisms underlying addiction, concluding that it may lead to the user having problems with addiction later in life.

Rich Birkett, who was an organizer of Ann Arbor’s Hash Bash in the late-80s and the 90s, disputes that smoking marijuana makes you more suseptible to addiction.

“I think the curiostiy to try other drugs is largely a social thing: what are your friends doing?” Birkett said.

According to Heitzeg, other studies involving marijuana are “cross-sectional” and take “snapshot” looks at the affects of use versus no use on the brain at one time. Heitzeg said the study she helped head up was different because it tracked the affects of marijuana use over time, which she hopes makes the study less suseptible to be biased by factors other than the drug’s affect on brain function.

“This is just one piece of evidence that points to the effects of substances on the brain and marijuana in particular,” she said.

Birkett, who moved to Guadalajara, Mexico from Ann Arbor in 2009, said he smokes marijuana for its medical benefits.

“I appear to be younger than I am,” he said.

According to the study, there are low perseptions of harm connected with marijuana, even though there are documented short-term and long-term consequences connected to its use.

Marijuana was approved for limited medical use by the state government through a voter referendum in 2008, and the Michigan Medical Marihuana Act was amended by the state legislature in 2012. Anyone over 18 years old who obtains a medical marijuana license can grow up to 12 plants for their own use; licensed caregivers can grow for up to 5 patients as well as themselves if they have a medical marijuana license.

The group MI Legalize filed a suit against the state in the court of claims in June to get their proposal to legalize recreational marijuana reinstated on the ballot this November. This week Michigan officials asked the court to throw out MI Legalize’s suit.

Marijuana is currently still a schedule 1 drug under federal law.

According to the study, marijuana is the most commonly used illicit substance in the U.S. and is even more common among young adults. It reported that 35 percent of 21- and 22-year-olds said they used the drug in 2014.

(313) 222-2613

Twitter: @evancarter_94