Long-term Cannabis Users Have Higher Levels of Brain Protein Linked to Stress and Anxiety
A new study has shown that long-term young adult cannabis users and those with cannabis use disorder, had significantly higher levels of a specific brain protein linked to chronic stress and anxiety, when compared to non-users. The same cannabis users also had higher levels of inflammatory markers in their blood, when compared to non-users.
The study, carried out by a collaboration of researchers in Toronto, Canada, and New South Wales, Australia, was published last week in the journal JAMA Psychiatry.
Brains of cannabis users show higher expression of translator protein
The study compared 24 long-term cannabis users, who had used cannabis for greater than a year, with 27 non-cannabis-using controls. Levels of neuroimmune activation and 18-kDa translator protein (TSPO) were examined and the presence of any links between brain TSPO levels, behavioral measures, and inflammatory blood biomarkers were investigated, for both groups.
Using a positron emission tomography (PET) tracer developed by the Centre for Addiction and Mental Health, the researchers found that the young cannabis users (mean age, 23.1 years) showed a 23.3 percent higher neuroimmune activation or TSPO levels than the control non-user group (mean age, 23.6 years), with this increasing to 31.5 percent in the subgroup affected by a cannabis use disorder.
Higher levels of stress and anxiety were associated with these increased TSPO levels in the brain, furthermore circulating blood levels of C-reactive protein – a substance produced by the liver in response to inflammation – were also increased.
These results came as a surprise to the researchers, who had hypothesized that the opposite might be true, given how often medical cannabis is recommended for its anti-inflammatory properties and how many recreational users testify using cannabis to relax.
"Having a hypothesis disproven this clearly is rare, but this is a strong finding," said senior study author Dr Romina Mizrahi of the University of Toronto, to CTVNews.
While increases in inflammation and stress-related markers may sound worrying, other experts in the field have confirmed that these results are not cause for alarm.
"This is just what we call an observational study – you take one group, take another group," said Dr Suresh Muthukumaraswamy, of the University of Auckland’s Centre for Brain Research, speaking on The AM Show.
”What you can't do based on that is say that cannabis has caused these people to have more inflammation. It could be something else – it could be they have more stress in life. You just don't know. It's not the type of study that allows you to make that kind of inference.”
Future study planned on chronic cannabis use and inflammation
The study researchers themselves are also keen to emphasize that this study does not necessarily prove a link between cannabis use and stress, anxiety or inflammation. Instead, they would like to see these exploratory correlations confirmed in other studies with a larger sample size.
Beyond this, Dr Mizrahi says the next research step is to investigate whether TSPO levels normalize following cannabis abstinence, and if this normalization is also reflected in the young person’s stress and anxiety levels.
“We are hoping we can replicate and expand this finding to further evaluate if this biomarker goes back to normal levels after people abstain from cannabis use,” said Dr Mizrahi in a statement.
“Cannabis is the most commonly used illicit drug in the world, but we know very little about the impact it has on the brain, especially in young users whose brains are still developing until the age of 25,” she explains. “These findings are an important step forward, but more studies are needed to better understand the role of cannabinoids and neuroimmune signaling.”