The grey area: Cannabis and cognitive impairment

Since the 3rd millennium BC (from the early to middle Bronze Ages), cannabis has been inhaled as a recreational drug worldwide. As the most common drug to be taken, 6.9% of the population take cannabis each year compared to the next most common drug, powder cocaine (of which 2.2% of the population have taken in the last year). The drug is grown in plant form, and the active ingredient is termed THC (tetrahydrocannabinol). Cannabis is a psychoactive drug, which means it acts on the central nervous system.

Within both the brain and the peripheral nervous system, there are cannoid receptors, known as CB1 and CB2. Normally, human chemicals (such as anandamide) bind to these receptors, and are responsible for the regulation of appetite, pleasure and motivation. Cannabis is delivered quickly to the brain, where it can activate these receptors and trigger the aforementioned pathways, resulting in the ‘high’ many users experience – followed by the munchies.

Cannabis is often thought of as the ‘safest drug’ due to the body’s inability to overdose on THC, but there are many long-term side effects that are not often considered. Many scientists suggest that long term dependence on cannabis could either lower an individual’s intelligence, or possibly increase the chances of psychological issues in later life.

The ‘Children of the 90s’ study followed 2000 adolescents from Bristol, aiming to establish any links between cannabis use and a decline in intelligence. This was done by testing the children’s IQs when they were 8 years old, and then comparing these results with other tests taken when the children were 15, and their GCSE results. Cannabis use was continually noted, to see if there was any correlation between usage and grades. The study found that there was no link between occasional cannabis use and loss of achievement.

However, the study uncovered a link between heavy usage (more than 50 times before the age of 15) and poorer-than-expected exam results, suggesting that excess cannabis may reduce IQ during adolescence. One criticism of this study is that there is no way to say that cannabis was the definitive cause of poorer results. Many of the heavy users were also involved in alcohol/other drug abuse, and various other risk factors. As a result, this study cannot conclude that cannabis reduces intelligence.

On the other hand, a study released in 2012 followed a sample of New Zealanders. Participants were interviewed at 13 years old, and again at 38 years, between which they were using cannabis. The scientists found that there were several cognitive problems for persistent cannabis users, and excess use was associated with greater intellectual decline. Also, neuropsychological function was not restored upon the stopping of usage. It was concluded that ‘findings are suggestive of a neurotoxic effect of cannabis on the adolescent brain, and highlight the importance of prevention and policy efforts targeting adolescents.’

All this conflicting research suggests that the medical community are unsure on the long-term effects of cannabis on the brain, but with the legalisation and decriminalisation of cannabis possession gaining success in many countries/states worldwide, it’s still a very pressing matter.


Hilary Robinson


Feature Image: High Times

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