Popular use of cannabis has grown so much over the past decade or so that it seems like people believe that using marijuana products is safe and effective, regardless of whether it’s for recreational or medical purposes. The truth is, though, that long-term use of marijuana is known to slow the pre-frontal cortex of the brain—the place where executive functioning happens. The research just doesn’t match the enthusiasm, and this is especially concerning for our teenagers.

Now, researchers from the Université de Montréal Faculty of Medicine and CHU Sainte-Justine in Canada have reported study findings showing that the active ingredient in cannabis—called THC or tetrahydrocannabinol—causes shrinkage of the growing of branches on neurons in the brains of adolescents. Those job of those branches is to connect with other neurons, and a reduction in the ability to connect with other neurons is not helpful. Neuroscience News reported that this causes atrophy in the cortex (the outer layer of the brain that has the grooves and ridges we recognize), calling that “bad news at a time when the brain is maturing.” I do not have a link to the study, published in the Journal of Neuroscience, at this time, but the abstract is available here. Neuroscience News covered this issue in more depth, and in an easy-to-understand manner, here.