Teens today are smoking less and drinking less than they used to – but they are using cannabis more. A little under 35 percent of American tenth graders have tried it at least once as it increasingly becomes their first drug of choice.
While there are countless studies examining the effect of cannabis on the teenage brain (to mixed results), very few have considered potential ramifications of low-level use. That is something researchers at the University of Vermont (UVM) want to change and so they started by looking at structural changes to the brain in teens after just one or two smokes. The study was published in The Journal of Neuroscience.
The bad news is that smoking cannabis just once or twice may be enough to change the structure of areas linked to emotion and memory. Though the researchers are not yet sure what exactly these changes mean in practical terms.
The study involved a group of 14-year-olds from Ireland, England, France, and Germany, who were each part of a long-term project called IMAGEN. Within this group, were 46 teens who had reported using cannabis once or twice before their 14th birthday.
Scans revealed that there were higher volumes of gray matter in cannabinoid receptors, a group of cell membrane receptors involved in appetite, pain-sensation, mood, and memory, in those who had taken cannabis, even at such low levels. The most noticeable changes were in areas called the amygdala (associated with fear and other emotion-related processes) and the hippocampus (associated with memory development and spatial abilities).
"Consuming just one or two joints seems to change gray matter volumes in these young adolescents," senior author Hugh Garavan, UVM professor of psychiatry, said in a statement.
These changes to the structure of the brain occurred even after controlling for variables like sex, socioeconomic status, and personality traits as well as nicotine and alcohol use, suggesting they are a direct consequence of cannabis use.
Garavan points out that at this age, our brains go through a period of "pruning". That is, it gets thinner as it refines and improves its synaptic connections. Garavan suggests that smoking cannabis disrupts this process.
It would explain why gray matter in the cannabis users was thicker than the gray matter in the non-users. However, right now it is just a hypothesis. It may also be that using cannabis led to the development of more neurons. It's also not entirely clear what this increase in gray matter means, practically speaking. Is it enough to negatively affect memory formation, for example?
That's something future studies will have to examine, along with the effect of different potencies of the drug and the age of first use. However, it's no doubt something we'll hear more of as states across the US look to legalize the drug.