According to a new study some regions of the brain may actually shrink with heavy long-term marijuana use. Mural Yücel, Ph.D., of the University of Melbourne, and colleagues, used magnetic resonance imaging to measure various regions of the brain in the participants. According to the cross-sectional study, the hippocampus and the amygdala were found to be “significantly smaller” in heavy long-term users. These regions of the brain are abundant in cannabiniod receptors, which would likely be affected if heavy long-term use of marijuana were toxic. According to the researchers, “the results… suggest that heavy daily use might indeed be toxic to human brain tissue.” The following is an excerpt of an article from Medpage Today that reviews the study:
While other studies have looked at changes in the brain associated with use of marijuana, they have not been found before, perhaps because instruments were not sensitive enough or the use of marijuana wasn’t heavy enough, the researchers said.
For this study, the researchers enrolled 15 men who had smoked more than five joints a day for more than 10 years, but who did not have other co-morbid drug use or neurological or psychiatric illness.
On average, the men had used marijuana for nearly 20 years.
They were contrasted with 16 matched controls who did not use the drug.
The volunteers took tests for subthreshold psychiatric symptoms and verbal learning ability, as well as being scanned in a high-resolution, three-Tesla MRI machine.