Cannabis use disorder in adolescence has long been something of a black box. 

Normally, researchers would use PET scans to detect abnormally low or high levels of dopamine in the brain, a common sign of drug addiction. But PET imaging, which uses radioactive tracers, is unsafe for use with adolescents.

Assistant Professor Sarah Thomas, Ph.D., a research scientist and clinical psychologist at Bradley Hospital, has struck on an alternative. In a pilot study, Thomas used an MRI machine to measure iron in brain tissues, a recently discovered indicator of dopamine synthesis that’s been used in studies with other drugs. She found that adolescents who use cannabis do, in fact, show lower levels of tissue iron, and thus likely, lower dopamine.

“No one’s ever done this in adolescents before,” she said. “It's especially relevant because the dopaminergic system is developing during this time of life. Without imaging, we’d have no idea how cannabis is affecting these developing systems.”

Now, Thomas is setting out to learn more about the correlation between cannabis use and blunted dopamine synthesis in adolescents, thanks to $132,000 in funding from a newly announced Zimmerman Innovation Award. The award, given by the Carney Institute for Brain Science, funds brain science research that has the potential to advance science and society in significant, lasting ways. 

“It’s incredibly valuable for me to be able to take the next steps in my research and start to look at how adolescent cannabis use affects their brain and behavior over time,” Thomas said.

Time is the key ingredient of Thomas’s study, which will measure adolescents’ dopamine levels, via tissue iron, over a period of three months. If those levels dip with repeated cannabis use, it would establish a stronger link between cannabis use and lower dopamine.

Low levels of dopamine, the chemical of the brain’s reward system, are thought to play a role in cannabis addiction: If a person has low dopamine, they may experience less pleasure from everyday activities and return to the drug for an artificial boost. 

“Adolescents who use cannabis have a much greater likelihood of becoming addicted to cannabis than adults do, and they also progress more quickly to their first symptom of cannabis use disorder within a year compared to adults,” Thomas said. “There's something happening that is putting them at a lot more risk.”

Low dopamine may lead to other mental health issues, as well.

“Dopamine is implicated in a lot of psychiatric disorders, whether there’s too much or too little,” Thomas said. “One question is whether low dopamine in the context of adolescent cannabis use can open the door for depressive symptoms, as well.”

In addition to brain scans, Thomas will also conduct behavioral tasks with participants to track changes in motivation.

She hopes the findings from her award-funded study could lay the groundwork for future studies that follow adolescent cannabis use and dopamine levels over longer periods of time. 

“Adolescence is such a dynamic time of development,” Thomas said. “We could be missing a lot that is happening.”