What long-term cannabis use can do to your brain

Cannabis use is a topic of fervent debate among researchers. As the drug is being legalized in an increasing number of countries, and as its medicinal properties have come into sharp focus, the experts ask to what extent it and its medicinal derivatives are helpful, and to what extent harmful.

Some use cannabis for recreational purposes, whereas others use cannabis-based drugs or essential oils to relieve chronic pain or treat epilepsy.

Recently, scientists at two academic institutions — Universidade de Lisboa in Portugal and the University of Lancaster in the United Kingdom — have conducted a study into long-term use of cannabis and its potential dangers.

The scientists' findings — published in the Journal of Neurochemistry — indicate that there is one important danger: regular cannabis use could impair a person's memory.

Going forward, as cannabis compounds are increasingly legalized and marketed for therapeutic use, we should consider what the downsides of cannabis use may be and how to address them, says study author Ana Sebastião.

Pitting potential harms against benefits

In the new study, Sebastião and colleagues focused on one cannabinoid-like compound called WIN 55,212-2 and observed its effects on the brain.

The researchers worked with a mouse model and found that, after long-term exposure to this drug, the rodents displayed "significant memory impairments." They were actually unable to distinguish between an object that they should have been familiar with and an object newly introduced to them.

By using brain imaging techniques, the researchers also saw that this drug affects brain regions that are involved in processes of learning, storing, and accessing memories.

Chronic exposure to this substance, explain Sebastião and team, further affects the brain, impairing the "communication" between brain regions that drive learning and memory.

"Importantly," notes Sebastião, "our work clearly shows that prolonged cannabinoid intake, when not used for medical reasons, does have a negative impact in brain function and memory."

"It is important to understand that the same medicine may re-establish an equilibrium under certain diseased conditions, such as in epilepsy or multiple sclerosis, but could cause marked imbalances in healthy individuals."

Ana Sebastião

"As for all medicines, cannabinoid-based therapies have not only beneficial disease-related actions, but also negative side effects," she adds.

A need for preventive strategies

These findings follow from previous research conducted by Sebastião's team, which also found that long-term cannabinoid use affects recognition memory. This is the type of memory that allows us to recall people or things that we have already encountered.

In their other study, the researchers even suggested a way of offsetting this negative outcome: by using a caffeine-related drug.

"These results are very important for the development of pharmacological strategies aiming to decrease cognitive side effects of currently used cannabinoid-based therapies, which proved effective against several nervous system disorders," notes Sebastião.

In the future, the scientists hope that a better understanding of cannabinoid drugs' harmful effects will lead to the development of strategies to counteract them.

"This work offers valuable new insight into the way in which long-term cannabinoid exposure negatively impacts on the brain," says study co-author Neil Dawson.

"Understanding these mechanisms," he adds, "is central to understanding how long-term cannabinoid exposure increases the risk of developing mental health issues and memory problems; only its understanding will allow to mitigate them."