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Home > News > Science & Health > Content Piece

Misleading Press Coverage Could Impact Use of Medicinal Cannabis

Published: Aug 14, 2018   
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A new study led by Ana Sebastião, group leader at Instituto de Medicina Molecular João Lobo Antunes and Professor of Faculdade de Medicina of Universidade de Lisboa (iMM, FMUL; Portugal) and her team in collaboration with researchers from the University of Lancaster (UK), apparently shows that the long-term use of cannabis-based drugs impairs memory. The study now published in the Journal of Neurochemistry claims to reveal the implications for both recreational users and people who use the drug to combat epilepsy, multiple sclerosis, and chronic pain.

Through the legalization in several countries of cannabis or cannabis-based drugs, there is an increased number of long-term users and more potent varieties are available for recreational users. It is already thought that heavy, regular cannabis use can increase the risk of developing mental health problems including psychosis and schizophrenia. However, there is still little evidence to support the potential negative side effects of long-term cannabinoid exposure.

The research group led by Ana Sebastião in collaboration with Neil Dawson and his team at Lancaster University studied the effects of a specific cannabinoid drug (named WIN 55,212-2) and found that long-term exposure in mice had "significant memory impairments". The study reports that the mice could not even discriminate between a familiar and novel object. The team also say that brain imaging studies show that the drug impairs function in key brain regions involved in learning and memory. Moreover, they say that long-term exposure to the drug impairs the ability of brain regions involved in learning and memory to communicate with each other.

"Importantly, our work clearly shows that prolonged cannabinoid intake, when not used for medical reasons, does have a negative impact on 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. As for all medicines, cannabinoid-based therapies have not only beneficial disease-related actions, but also negative side effects," says Ana Sebastião. A previous study from the same team has shown that acute exposure to cannabinoids results in recognition memory deficits, an effect that can be prevented by the use of a drug of the family of caffeine. "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," explains Ana Sebastião.

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

It is worth mentioning that the results reported in this study are not necessarily indicative of broader negative effects resulting from cannabis use. Two key points must be taken into consideration when assessing the reported findings. 

  1. The researchers did not use cannabis. They used a synthetic cannabinoid, WIN55,212-2, which acts on the same receptors as CBD and THC. The negative health effects of synthetic cannabinoids are already fairly well understood and are entirely separate from natural cannabis. 
  2. The study was conducted using mice so extrapolating the team's findings out to humans is questionable at best.   

Further research is certainly required to better understand the potential side effects of cannabis-based treatments. But, the real lesson here is that early stage research should be treated with care and, carefully scrutinized when it makes it into the media. 

This article has been republished from materials provided by Instituto de Medicina Molecular. Note: material may have been edited for length and content. For further information, please contact the cited source.


Mouro, F. M., Ribeiro, J. A., Sebastião, A. M., & Dawson, N. (2018). Chronic, intermittent treatment with a cannabinoid receptor agonist impairs recognition memory and brain network functional connectivity. Journal of neurochemistry.


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