New research casts doubts on claims that chronic cannabis use results in “amotivational syndrome,” which is characterized by a lack of enjoyment of everyday life and a loss of motivation. The study, published in the International Journal of Neuropsychopharmacology, found no difference in anhedonia, apathy, or motivation between cannabis users and non-users.
“Cannabis is the third most commonly used controlled substance worldwide, and with its legal profile currently changing in many countries it is more important than ever to know how cannabis affects the brain and cognition,” said study author Martine Skumlien, a PhD candidate in the Department of Psychiatry at the University of Cambridge. “One common trope frequently perpetuated in movies, TV shows, and anti-cannabis PSAs is that of ‘the lazy stoner,’ which displays cannabis users as lazy, demotivated, and apathetic. However, this is based on a stereotype and not on scientific evidence.”
The researchers recruited 76 adolescents and 71 adults from the Greater London area who had been using cannabis 1 to 7 days per week, on average, over the past three months. Adolescents were 16-17 years of age, while adults were 26-29 years of age. The cannabis-using participants were matched with 63 adolescents and 64 adults who did not use cannabis.
“We compared teen and adult cannabis users and controls from the large MRC-funded UCL CannTeen study on several measures of reward and motivation, including apathy and willingness to expend physical effort for reward,” Skumlien told PsyPost.
The participants completed a measure of anhedonia known as the Snaith-Hamilton Pleasure Scale, in which they indicated the extent to which they agreed or disagreed with statements such as “I would find pleasure in my hobbies and pastimes” and “I would find pleasure in small things, e.g. bright sunny day, a telephone call from a friend.”
The participants also completed a questionnaire known as the Apathy Evaluation Scale, in which they indicated how well statements such as “I am interested in things” and “Getting things done during the day is important to me” applied to them.
The researchers found that cannabis users scored slightly lower than non-users on the Snaith-Hamilton Pleasure Scale, suggesting that they are better able to enjoy themselves. But there was no significant difference when it came to apathy. Skumlien and her colleagues also found no correlation between cannabis use frequency and anhedonia or apathy.
In addition, 139 participants completed two task-based measures of motivation, which assessed the willingness to expend effort for reward, reward sensitivity, effort sensitivity, reward wanting, and reward liking.
In the first task, 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, participants were first told to estimate how much they wanted to receive each of three rewards (30 seconds of one of their favourite 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.”
In line with the self-reported questionnaires, the researchers found no difference between cannabis users and non-users on either task. “I was somewhat surprised to find that the groups weren’t any different on the measures, as this is not what we hypothesised,” Skumlien told PsyPost. “We also expected adolescent cannabis users to be worse off than the adult users, as drug use in adolescence is often thought to be particularly harmful. However, we found no evidence of such adolescent vulnerability.”
“In short, we found no support for the idea that cannabis use is linked with amotivation,” the researcher said.
Co-author Will Lawn added in a news release: “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,” Lawn said. “However, we need studies that look for these associations over a long period of time to confirm these findings.”
The findings provide evidence that cannabis use is not associated with persistent disruption to reward processing in adults or adolescents. But it is still possible that cannabis induces acute disruptions in reward processing.
“Crucially, participants in our study had not used any cannabis prior to participating. It is therefore still possible that people find themselves less motivated to do certain things while they are high,” Skumlien explained. “We plan to look at this in a future investigation from the CannTeen study! It is also worth emphasizing that motivation is a broad concept, and measures that assess motivation in a laboratory setting may not always translate to real-life situations.”
“Stereotypes can be stigmatizing and get in the way of harm-reduction messages around drug use,” Skumlien added. “We need to be honest about what are and are not potential consequences of cannabis use, and not use harmful and untrue stereotypes in efforts to discourage people from using cannabis.”
The study, “Anhedonia, apathy, pleasure, and effort-based decision-making in adult and adolescent cannabis users and controls“, was authored by Martine Skumlien, Claire Mokrysz, Tom P. Freeman, Vincent Valton, Matthew B. Wall, Michael Bloomfield, Rachel Lees, Anna Borissova, Kat Petrilli, Manuela Giugliano, Denisa Clisu, Christelle Langley, Barbara J. Sahakian, H. Valerie Curran, and Will Lawn.
