Cannabis can both help and hinder memory. How it affects you might come down to inequality

The idea that cannabis impairs memory has been around so long it’s almost accepted as fact. But science is coming to a more nuanced understanding

Ian Hamilton
Wednesday 22 July 2020 08:16 BST
David Lammy visits cannabis factory in Canada

Even the word “dope”, describing people that use cannabis, suggests they have less than optimal brain functioning. The idea that cannabis impairs memory has been around so long it’s almost accepted as fact. The science exploring the relationship between cannabis and memory is now revealing a far more interesting understanding of the connection.

There is evidence of disruption to short-term memory and concentration during intoxication with cannabis. Both are responsible for the poorer educational outcomes in adolescents who were observed in research. That’s why Duncan Bannatyne, of Dragons’ Den fame, made a deal with his children that to receive their inheritance they should refrain from using drugs like cannabis until they reached 21 years old. Although using cannabis in your twenties disrupts memory functioning at least you’ve finished your education, which relies on memory for success.

But this isn’t the whole story. Recent research has found that compounds found in cannabis can delay the onset of problems like dementia and Alzheimer’s. Cannabis naturally generates neurons, which is important as diseases like these not only cause depletion but also interfere with the networks between them. This is an important finding given the rapidly growing ageing population and the lack of treatments for these debilitating diseases.

This seemingly paradoxical evidence where cannabis both hinders and helps memory can be explained by what’s in cannabis. Cannabis usually has both tetrahydrocannabinol (THC) and cannabinoids (CBD). THC is the compound that gets people high while CBD is able to dampen this effect; cannabis with higher levels of THC and lower CBD will create a more intense experience. Higher THC potency appears to disrupt working memory during intoxication. So, it is the ratio of THC and CBD that accounts for the seemingly contradictory effects on memory. In recent years the type of cannabis available has more THC and less, if any, CBDs.

The good news is that even for young people whose memory is impaired when using cannabis, this isn’t permanent provided they abstain in future. In effect any damage can be reversed.

A useful reminder of how little we know about this drug is the impact on the sexes and their memory. We now know that young girls experience more severe memory impairment than their male peers, but we don’t know why.

What is clear is that just like many other drugs, including alcohol, the more frequently cannabis is used and the greater the quantity consumed, the greater the risk of memory impairment. For those young people that try drugs, some, if not most young people will use more than one substance at a time, for example alcohol and cannabis. This makes research difficult when trying to establish cause and effect, as both alcohol and cannabis are known to interfere with memory, but it is difficult to discern the extent that each contributes.

Drug use and its impact is not spread equally. While hundreds of thousands of young people will use cannabis, only a small proportion will go on to use the drug regularly and heavily. There is a trend of fewer young people using any drugs at all, but a small proportion are bucking this generational shift. Lower potency cannabis carries a smaller risk than higher potency, and unfortunately most young people are unable to access lower potency varieties.

These young people could be severely disadvantaged as their cannabis consumption, with or without alcohol, could reduce their ability to study and therefore what they achieve educationally. There’s little comfort in knowing that the effects of cannabis on memory can be reversed if you have already failed exams or other key educational outcomes. Not only does this risk lowering their confidence but reduces the opportunity of fulfilling their potential.

Young people need all the help they can get in entering the shrinking job market.

They may have to forgo a rite of passage that baby boomers enjoyed if they want to escape unemployment and all the inequality that yields. No matter how enticing and enjoyable a joint might seem, the evidence on health impacts remains mixed. Until we get more consistent and clearer research, young people are often left to assess the risks themselves.

Ian Hamilton is associate professor of addiction at the University of York

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