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By UNIVERSITY OF CAMBRIDGE
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Additionally,
compared to non-users, cannabis users exhibit no differences in reward-seeking
motivation, enjoyment from rewards, or the brain’s response to rewards.
After
alcohol and nicotine, cannabis is the third most often used controlled
substance globally. According to 2018 research from the NHS Digital Lifestyles
Team, 19% of 15-year-olds in England reported using cannabis in the previous
year. This number was higher in the United States, with the National Institute
on Drug Abuse reporting that 28% of 15 to 16-year-olds used cannabis in the
previous 12 months in 2020.
The
“stoner” is a prevalent stereotype of cannabis smokers; think Jesse Pinkman in
Breaking Bad, The Dude in The Big Lebowski, or, more recently, Argyle in
Stranger Things. These are people who are often portrayed as lazy and uncaring.
At the same time, there has been a great deal of worry about the possible effects of cannabis usage on the growing brain and the possibility that consuming cannabis throughout adolescence may have negative effects at a crucial time in a person’s life.
A
study was conducted to determine whether cannabis users exhibit higher levels
of apathy (loss of motivation) and anhedonia (loss of interest in or pleasure
from rewards) when compared to controls and whether they were less willing to
exert physical effort to receive a reward. The study was led by a team of
researchers from University College London, the University of Cambridge, and the Institute of
Psychiatry, Psychology & Neuroscience at King’s College London. The research was part of the
CannTEEN study.
The
findings were recently published in the International Journal of
Neuropsychopharmacology.
The
team recruited 274 adolescent and adult cannabis users who had used cannabis at
least weekly over the past three months, with an average of four days per week,
and matched them with non-users of the same age and gender.
Participants
completed questionnaires to measure anhedonia, asking them to rate statements
such as “I would enjoy being with family or close friends”. They also completed
questionnaires to measure their levels of apathy, which asked them to rate
characteristics such as how interested they were in learning new things or how
likely they were to see a job through to the end.
Cannabis
users scored slightly lower than non-users on anhedonia – in other words, they
appeared better able to enjoy themselves – but there was no significant
difference when it came to apathy. The researchers also found no link between
the frequency of cannabis use and either apathy or anhedonia in the people who
used cannabis.
Martine
Skumlien, a Ph.D. candidate in the Department of Psychiatry at the University
of Cambridge, said: “We were surprised to see that there was really very little
difference between cannabis users and non-users when it came to lack of
motivation or lack of enjoyment, even among those who used cannabis every day.
This is contrary to the stereotypical portrayal we see on TV and in movies.”
In
general, adolescents tended to score higher than adults on anhedonia and apathy
in both user and non-user groups, but cannabis use did not augment this
difference.
Dr.
Will Lawn, from the Institute of Psychiatry, Psychology, and Neuroscience at
King’s College London, said: “There’s been a lot of concern that cannabis use
in adolescence might lead to worse outcomes than cannabis use during adulthood.
But our study, one of the first to directly compare adolescents and adults who
use cannabis, suggests that adolescents are no more vulnerable than adults to
the harmful effects of cannabis on motivation, the experience of pleasure, or
the brain’s response to reward. In fact, it seems cannabis may have no link –
or at most only weak associations – with these outcomes in general. However, we
need studies that look for these associations over a long period of time to
confirm these findings.”
Just
over half of the participants also carried out a number of behavioral tasks.
The first of these assessed physical efforts. Participants were given the
option to perform button-presses in order to win points, which were later
exchanged for chocolates or sweets to take home. There were three difficulty
levels and three reward levels; more difficult trials required faster button
pressing. On each trial the participant could choose to accept or reject the
offer; points were only accrued if the trial was accepted and completed.
In
a second task, measuring how much pleasure they received from rewards,
participants were first told to estimate how much they wanted to receive each
of three rewards (30 seconds of one of their favorite songs, one piece of
chocolate or a sweet, and a £1 coin) on a scale from “do not want at all” to
“intensely want”. They then received each reward in turn and were asked to rate
how pleasurable they found them on a scale from “do not like at all” to
“intensely like”.
The
researchers found no difference between users and non-users or between age
groups on either the physical effort task or the real reward pleasure task,
confirming evidence from other studies that found no, or very little,
difference.
Skumlien
added: “We’re so used to seeing ‘lazy stoners’ on our screens that we don’t
stop to ask whether they’re an accurate representation of cannabis users. Our
work implies that this is in itself a lazy stereotype and that people who use
cannabis are no more likely to lack motivation or be lazier than people who
don’t. Unfair assumptions can be stigmatizing and could get in the way of messages
around harm reduction. We need to be honest and frank about what are and are
not the harmful consequences of drug use.”
Earlier
this year, the team published a study that used functional magnetic resonance
imaging (fMRI) to look at brain activity in the same participants as they took
part in a brain imaging task measuring reward processing. The task involved
participants viewing orange or blue squares while in the scanner. The orange
squares would lead to a monetary reward, after a delay, if the participant made
a response.
The
researchers used this setup to investigate how the brain responds to rewards,
focusing in particular on the ventral striatum, a key region in the brain’s
reward system. They found no relationship between activity in this region and cannabis
use, suggesting that cannabis users had similar reward systems as non-users.
Professor
Barbara Sahakian, from the Department of Psychiatry at the University of
Cambridge, said: “Our evidence indicates that cannabis use does not appear to
have an effect on motivation for recreational users. The participants in our
study included users who took cannabis daily and they were no more likely to
lack motivation. However, we cannot rule out the possibility that greater use,
as seen in some people with cannabis-use disorder, has an effect. Until we have
future research studies that follow adolescent users, starting from onset
through to young adulthood, and which combine measures of motivation and brain
imaging, we cannot determine for certain that regular cannabis use won’t
negatively impact motivation and the developing brain.”
References:
“Anhedonia,
apathy, pleasure, and effort-based decision-making in adult and adolescent
cannabis users and controls” by Martine Skumlien, MRes, Claire Mokrysz, Ph.D.,
Tom P Freeman, Ph.D., Vincent Valton, Ph.D., Matthew B Wall, Ph.D., Michael
Bloomfield, Ph.D., Rachel Lees, MSc, Anna Borissova, MBBS, Kat Petrilli, MRes,
Manuela Giugliano, MSc, Denisa Clisu, MSci, Christelle Langley, Ph.D., Barbara
J Sahakian, Ph.D. DSc, H Valerie Curran, Ph.D. and Will Lawn, Ph.D., 24 August
2022, International Journal of Neuropsychopharmacology.
DOI:
10.1093/ijnp/pyac056
“Neural
responses to reward anticipation and feedback in adult and adolescent cannabis
users and controls” by Martine Skumlien, Claire Mokrysz, Tom P. Freeman,
Matthew B. Wall, Michael Bloomfield, Rachel Lees, Anna Borissova, Kat Petrilli,
James Carson, Tiernan Coughlan, Shelan Ofori, Christelle Langley, Barbara J.
Sahakian, H. Valerie Curran and Will Lawn, 6 April 2022, Neuropsychopharmacology.
DOI: 10.1038/s41386-022-01316-2
The
study was funded by the Medical Research Council with additional support from the
Aker Foundation, National Institute for Health Research, and Wellcome.