A recent study suggests that long-term cannabis use may be linked to changes in brain structure and function, though it’s not certain that cannabis itself is the cause.
This research, published in BMJ Mental Health, looked at data from nearly 16,000 people in the UK Biobank who had brain imaging and genetic profiling.
With cannabis becoming more common globally due to legalization for medical and recreational use, scientists are eager to understand its possible long-term effects on the brain.
While some studies have shown that cannabis use can harm brain function and structure, it’s unclear whether cannabis alone causes these changes.
The researchers used a technique called Mendelian randomization, which involves using genetic data to study cause-and-effect.
By comparing genetic links to cannabis use with brain structure, the researchers aimed to see if the associations were due to cannabis or other factors.
Participants were asked if they had ever used cannabis, ranging from “once or twice” to “more than 100 times.”
Those who had used cannabis at least once (3,641 people) were classified as lifetime users, while those who hadn’t (12,225 people) served as the comparison group. They also recorded how often people used cannabis and how long it had been since their last use.
After considering factors like age, sex, income, mental health, and lifestyle, the researchers found some brain differences in cannabis users.
Those who had used cannabis showed signs of lower white matter integrity in the brain—a structure vital for cognitive function, especially in an area called the corpus callosum, which helps the left and right sides of the brain communicate.
Cannabis users also had weaker connectivity in brain areas related to daydreaming or resting state, known as the “default mode network.” These regions contain many cannabinoid receptors, which are directly affected by cannabis.
Differences between men and women were also found. For men, the main changes were in functional connectivity, while for women, white matter integrity was primarily affected. However, the frequency or recentness of cannabis use didn’t seem to influence the findings.
Interestingly, when using Mendelian randomization to look at genetic links, there was no clear evidence that cannabis use caused these brain changes. This might mean that other factors, like family history or lifestyle, could be influencing these observations, or that Mendelian randomization might be missing some subtle effects.
The researchers note that their study has some limits. The UK Biobank participants were mostly healthy and white, so the findings might not apply to other groups. Also, some data relied on participants’ memory of their cannabis use, which may not always be accurate.
While the findings are significant, more research is needed to fully understand cannabis’s impact on the brain, especially heavy use and cannabis potency.
The researchers stress that these results should be interpreted carefully, as they aim to provide more insight into public health.
