A team led by Indiana University clinical psychologist and neuroscientist William Hetrick has received a $3 million grant from the National Institutes of Health's National Institute on Drug Abuse to support research on the effects of long-term cannabis use on the brain of young adults, ages 18 to 38.

The award will address a large gap in knowledge about how marijuana affects the brain. It also adds to IU research related to substance use in the wake of the IU Responding to the Addictions Crisis Grand Challenge initiative.

IU researchers will focus on the brain systems most affected by marijuana: the neural networks within the cerebellum and those that connect the cerebellum to other brain regions.

Hetrick is a professor and chair in IU Bloomington College of Arts and Sciences' Department of Psychological and Brain Sciences. Collaborators on the award include professors Brian O'Donnell, Sharlene Newman, Ken Mackie and Olaf Sporns, and senior research scientists Amanda Bolbecker and Dae-Jin Kim, all in the Department of Psychological and Brain Sciences.

As marijuana legalization -- both medical and recreational -- increases across the U.S., its use has raced ahead of scientific understanding, Hetrick said, especially since cannabis' classification as a Schedule 1 substance under federal law has obstructed the usual channels of research and testing.

"Compounds in cannabis are rarely tested in the framework of a regular drug development process to determine, for example, which dosage has adverse effects, and which has optimal therapeutic effects," O'Donnell said. "This study seeks to expand the empirical basis for ultimately understanding the effects of marijuana use on brain function and behavior, and for discussing legalization."

"When you consider that 40 percent of all 19- to 22-year-olds in the U.S. used marijuana in the past year, it behooves us to understand how it affects its users," Hetrick added. "An obvious place to start is by asking, 'What's the effect on brain systems that are dependent on the brain's cannabinoid receptor system?'"

The chemical THC, which binds to cannabinoid 1, or CB1, receptors in the brain, is responsible for the "high" of marijuana. The greatest concentration of CB1 receptors are typically in the cerebellar region of the brain.