Since the late 1930s, cannabis, otherwise known as marijuana, has been a topic of great debate in the United States. Currently, many states have legalized marijuana or decriminalized it for recreational and medical use. Despite the growing movement to legalize recreational use for adults, Matthew Albaugh, professor at University of Vermont, explains that it can still be harmful for young users. He stated,“Brain areas that change the most during adolescence may be especially vulnerable to cannabis exposure.” There have been significant studies that indicate cannabis having brain altering effects on humans.
Albaugh and his team conducted a study with 799 14-year-olds throughout four European countries: Germany, France, Ireland, and England. The kids received MRI scans and five years later, the study was repeated with the same kids. During the second MRI, 46% of them said they had tried cannabis; approximately 75% said they had used the substance 10 or more times. The study showed that there was quite a contrast between the prefrontal cortex (which is responsible for decisions, impulses, and focus) of those who used cannabis and those who didn’t. The prefrontal cortex had thinned faster for those who used cannabis than those who didn’t, even more so for those who used it frequently. These results have been somewhat inconsistent since researchers can’t experiment with real teenagers. However, results do add to the existing data that supports the claim that cannabis affects the brain's development.
Jacqueline-Marie Ferland, brain researcher at Icahn School of Medicine, explains that the thinning of the prefrontal cortex is often connected to maturing, decision making, rationality, and managing impulsivity; a properly matured prefrontal cortex can perform these functions. However, another study on young animals shows that thinning too early can cause long term problems with behavior and memory.
A psychologist at Erasmus University, Janna Cousijn envisions the human brain as a thick forest. She says, “As we grow up, we often decide to take similar paths within that forest,” meaning that recurring connections start forming between brain cells as humans age. The more they get used, the faster the brain processes them. In contrast, the connections that are used less are forgotten over time. This takes place as the prefrontal cortex begins to thin.
Critically, THC (the psychoactive component in cannabis) attaches to CB1 receptors in brain cells since it’s perfectly structured to react to cannabis compounds. Another study consisted of giving THC to adolescent rats. The results of that study suggest that it sped up the thinning in that part of their brains which is equivalent to the “prefrontal cortex”. It was observed that they lost connections in their brains that usually stayed until their adulthood. These studies point towards the idea that cannabis might have caused alterations to their memory and behavior based on their age and the amount of THC they were given.
The researchers couldn't find a direct connection with THC and the prefrontal cortex's thinning in humans, but Albaugh's team found that 21 adult men in their research had more CB1 receptors in their prefrontal cortex. The area in the brain which contains more of the CB1 receptors coincidentally aligns with the part that thinned faster within teen cannabis users. This doesn't automatically mean that the usage of the substance causes the change, since the same experiments couldn't be ethically conducted on teenagers due to the radioactive material needed for the experiment; this leaves the teenage usage of cannabis and its effects on their brains still a hypothesis.
Albaugh continues his work to learn if thinning continues throughout adulthood and is now studying the same brain scans of his first subjects, now 23. In addition to this, he will include a test to see if brain changes that were previously reported relate to unfortunate outcomes such as lowered graduation rates, delayed graduation or mental health disorders. Ferland also voices that it’s important to know if teen cannabis usage can alter the way they operate in their adulthood.
Many researchers have advocated holding back on the usage of cannabis until adulthood, restricting the usage, and opting for low strength products since there is still more to be discovered from it. It is also important to remember that though cannabis might be harmful, both cigarettes and alcohol have been discovered to do more significant damage in comparison to cannabis. It is especially critical considering that alcohol is still one of the most prevalent drugs to be used by teenagers in several places around the world. Changes in the brain from continued substance use can cause addiction or increase the likelihood of becoming addicted in the future.
[Sources: Science News for Students; University of Vermont]