Introduction

Cannabis use has historically been linked with a lack of motivation, sometimes referred to as the ‘amotivational syndrome’ in the early scientific literature [1, 2]. Despite recent shifts towards more permissive cannabis legislation in many countries, pejorative ‘stoner’ stereotypes that portray people who use cannabis as lazy, demotivated, and apathetic are still very much alive in contemporary news and entertainment media [3, 4]. A recent public opinion survey found that ‘lazy’ and ‘irresponsible’ were among the five terms most commonly associated with cannabis by respondents [5] and typing ‘cannabis makes you…’ into the Google search engine yields ‘lazy’ and ‘dumb’ as the first suggestions. Although the ‘stoner’ trope has, to an extent, been reappropriated by some people who use cannabis, these stereotypes can cause harm by contributing to the stigma of cannabis use [6]. This can be especially harmful where cannabis stigma intersects with other sources of social inequality [7, 8] or prevents patients from accessing legal cannabis-based medicinal products [9, 10].

Δ9-tetrahydrocannabinol (THC), the main psychoactive compound in cannabis, acts on the endocannabinoid system, which plays an important role in regulating reward and motivational processes in the brain. Cannabinoid Receptor Type 1 (CB1R) agonists can enhance the motivational and reinforcing effects of food and drug rewards, while CB1R antagonists can attenuate these effects [11, 12]. Moreover, chronic THC exposure can lead to a downregulation of CB1Rs in humans and rodents [11, 13], including in the striatum [14], which is a key component of the brain’s reward network [15, 16]. Therefore, it is possible that prolonged cannabis exposure triggers neuroadaptations in the endocannabinoid system that alters its sensitivity rewards, which could manifest as reduced motivation [17].

However, the evidence supporting claims of a cannabis amotivational syndrome is anecdotal and has only recently been tested by scientific studies. We have previously reviewed the research on the association between cannabis use and reward processing, which is broadly defined as any process that underpins the seeking or consumption of rewards and includes motivation [18, 19•]. There was some evidence supporting an association between cannabis dependence and apathy, but there were only two studies at the time which explored the association between cannabis use and the willingness to expend effort for reward [20, 21]. Therefore, we were unable to draw any conclusions either in favour of or opposition to the cannabis amotivational syndrome. However, since then, several studies that investigate the relationship between both acute and non-acute cannabis exposure and motivation have been published.

In the current review, we take a look at recent research on the association between cannabis use and motivation, focusing on studies published in the last 5 years. We did not perform a systematic search of studies but identified relevant literature through our previous systematic review [19•], citation chaining, and PubMed alerts. Inclusion criteria were publication of original data in a peer-reviewed journal and assessment of the association between acute or non-acute cannabis exposure with a behavioural task-based or questionnaire measure of motivation in human participants. Studies were excluded if participants were recruited on the basis of primarily using a drug other than cannabis (except alcohol and/or tobacco use) or having a history of psychiatric disorder (other than cannabis use disorder, for the cannabis groups). Behavioural/task-based studies were classified according to whether they assessed motivation after acute exposure to cannabis or compared motivation in people who did and did not use cannabis non-acutely. As questionnaires mostly assess trait-level motivation, these all fell into the ‘non-acute’ category. Finally, we discuss potential neurobiological substrates of the putative association between cannabis use and motivation.

Is Cannabis Exposure Associated with Reduced Motivation?

Non-Acute Cannabis Use and Task-Based Measures of Motivation

Recent studies investigating the association between cannabis use and motivation are detailed in Table 1. Most operationalise motivation as willingness to expend effort for reward using the Effort Expenditure for Reward Task (EEfRT) [22], in which participants are required to press a button quickly and repeatedly a pre-set number of times in order to win a reward, which is usually money. On each trial, participants can choose between an easy/low-effort task or a hard/high-effort task, the latter requiring more or faster button-presses. Additionally, the reward magnitude and reward probability vary, yielding different expected values from trial to trial. Willingness to expend effort for reward is typically indexed by the percentage of high-effort trials chosen by the participant.

Table 1 Overview of recent studies investigating the association between cannabis use and motivation

Contrary to the amotivational hypothesis, recent research using the EEfRT suggests that cannabis users are more willing to expend effort for reward compared with controls. Acuff et al. [23], Taylor and Filbey [24], and Vele et al. [25] all found that young adult cannabis users selected a greater percentage of high-effort trials on the EEfRT relative to age-matched controls, regardless of reward magnitude and reward probability. These user-group differences corresponded to medium-to-large effect sizes of Cohen’s d = 0.54, ηp2 = .101, and ηp2 = .104, respectively. Moreover, both Acuff et al. and Taylor and Filbey found that frequency of cannabis use was positively associated with the likelihood of selecting a high-effort trial, suggesting people who used cannabis more frequently had greater motivation than people who used cannabis less frequently. Acuff et al. also found a positive association between selecting high-effort trials and symptoms of Cannabis Use Disorder (CUD).

However, in our own research, we have not found any differences between cannabis users and controls in willingness to expend effort for reward. We compared 68 adult and adolescent cannabis users with 69 age-matched controls from the ‘CannTeen’ study on the Physical Effort task (PhEft) [26•], which is similar to the EEfRT with the exception that rewards are not probabilistic and participants are given the option to accept or reject each trial (rather than choosing between a high-effort and low-effort option) which vary only in effort level and reward magnitude. We found no differences between cannabis users and controls on the overall number of accepted trials or effort sensitivity (number of accepted trials at the lowest effort level minus number of accepted trials at the highest effort level). We also found no differences between cannabis users and controls on reward sensitivity (number of accepted trials at the highest reward level minus number of accepted trials at the lowest reward level). These results are consistent with a previous study by Lawn et al. [21] which found no differences between 20 adult cannabis users and 20 controls on the EEfRT.

In summary, studies investigating the association between non-acute cannabis use and willingness to expend effort for reward have either found higher motivation in cannabis users or no difference between users and controls. Thus, this research does not support claims that using cannabis leads to a loss of motivation.

Acute Cannabis Exposure and Task-Based Measures of Motivation

All the studies discussed thus far measured willingness to expend effort after participants had been abstinent from cannabis for at least 12 h and therefore cannot address whether cannabis has acute amotivational effects that dissipate with abstinence. There are only two studies to date which have measured the effects of acute cannabis exposure on EEfRT performance, both of which found that participants had lower motivation on the task while they were high. In the most recent of these, Wardle et al. [27] looked at the effect of 7.5 or 15 mg ingested THC compared with placebo on EEfRT performance in 58 young adult women. While there were no significant differences between the different THC doses or between the 7.5 mg dose and placebo, the 15 mg dose decreased the likelihood of selecting a high-effort trial by 55% compared with placebo. Follow-up analyses showed that THC affected high-effort choices with moderate to high expected values (greater reward magnitude and probability) but not with low expected values. Lawn et al. [21] also measured the effect of 8 mg acute vaporised THC on EEfRT performance in 16 young adults and found that THC significantly reduced the likelihood of making a high-effort choice at low reward probability compared with placebo. THC also marginally increased the sensitivity to reward magnitude changes at low reward probability.

Of note, participants in these studies used cannabis on average 3.70 days per month (Wardle et al. [27]) and 8.06 days per month (Lawn et al. [21]). Acute cannabis studies typically exclude people who do not use cannabis to ensure that they are likely to tolerate the study drug and to minimise the risk of adverse effects. However, as prolonged cannabis use has been shown to increase the tolerance to acute effects in some [28] (though not all [29]) studies, cannabis-naïve participants may experience even stronger amotivational effects after acute cannabis exposure, and conversely, people who use cannabis daily may experience weaker effects. Moreover, although non-acute studies have not found an association between cannabis use and willingness to expend effort for reward, the acute research indicates that daily cannabis use may still result in a persistent amotivational state if it is used frequently and daily. Therefore, future studies should investigate the potential amotivational effects of both acute and non-acute cannabis exposure in people with daily cannabis use or cannabis dependence.

Non-Acute Cannabis Use and Questionnaire-Based Measures Motivation

The decision of whether or not to engage in an effortful activity to obtain a reward is subserved by a number of inter-related sub-processes such as option generation, hedonic impact of rewards, and reward learning [30]. A benefit of task-based measures of motivation is that one sub-process can, to some extent, be isolated and controlled to yield a quantifiable measure of another. A notable downside is that they may be poor approximations of real-life decision-making. For this reason, task-based data should be complemented by other measures of motivation when evaluating the relationship with cannabis use.

Several recent papers have investigated whether cannabis use is associated with apathy, defined as a loss of or reduction in the interest to seek rewards [31]. Petrucci et al. [32•] investigated correlations between 11 scales measuring various aspects of motivation, including the Apathy Evaluation Scale, and six cannabis use variables in a sample of 1168 participants. While any lifetime cannabis use was significantly associated with lower apathy (r = −.100), apathy correlated positively with quantity of use (r = .118), scores on the Cannabis Use Disorder Identification Test (r = .107), and scores on the Marijuana Problems Scale (r = .125), after controlling for depression, other substance use, and Big-5 personality traits. There were no significant associations with cannabis use frequency or age of onset. By contrast, in a 2-year longitudinal study of 401 adolescents, Pacheco-Colón et al. found no association between cannabis use and apathy either at baseline or over time [33•]. Similarly, there were no differences in apathy between adult and adolescent cannabis users and age-matched controls in the CannTeen study [26•]. Interestingly, in another study with 798 respondents conducted during the first UK COVID-19 pandemic lockdown, we found that adult cannabis users had lower levels of apathy compared with age-matched controls at a small-to-medium effect size of ηp2 = .048, while adolescent cannabis users and controls were no different [34]. However, exploratory follow-up analyses within cannabis users showed that those who were classified as dependent on the Severity of Dependence Scale had significantly higher levels of apathy than those who were classified as non-dependent, at a small-to-medium effect size of ηp2 = .037. As such, it could be that cannabis dependence or CUD, but not cannabis use per se, is linked with higher levels of apathy.

Recent research looking at other meaures of motivation has yielded mixed results. Lac and Luk [35] found that cannabis use predicted lower initiative and persistence, but not effort, on the General Self-Efficacy Scale in a longitudinal study of 505 college students. However, Petrucci et al. [32•] found no differences between young adult cannabis users and controls on the same scale, and no correlations between self-efficacy and any cannabis use measure. They also found no associations between cannabis use and mastery approach, mastery avoidance, and performance approach on the Achievement Goal Questionnaire. However, there is some evidence that frequent cannabis use is linked with academic motivation in adolescents. In the longitudinal study by Pacheco-Colón et al. [33•], cannabis use was associated with lower valuing of school on the Motivation and Engagement Scale (MES) at baseline, after controlling for covariates. Cannabis use was not significantly associated with any other MES factors. In a longitudinal study of 3265 adolescents by Schaefer et al. [36], cannabis use predicted decreased academic motivation on a six-item measure containing statements like ‘enjoys attending school’ and ‘motivated to earn good grades’. It could be that adolescents are more susceptible to potential amotivational effects of cannabis compared with adults [37,38,39,40] or that cannabis negatively impacts academic motivation in adolescents simply through more time being spent on using cannabis rather than on academic activities.

Finally, it is worth noting that cannabis users and non-users may differ on other reward sub-processes or psychological characteristics that are closely linked with motivation. In our previous systematic review, we found an association between cannabis use and anhedonia, defined as a loss of interest in or pleasure from previously rewarding experiences, in adolescents but not adults [19•]. Subsequent results from other studies [24, 34] are consistent with this finding. Moreover, risk-taking, novelty-seeking, and impulsivity may all affect effort-based decision-making for reward and are predictive of cannabis and other drug use [41, 42]. For instance, in another investigation with the CannTeen sample, Borissova et al. [43] found that both adolescents and adults who used cannabis had steeper delay discounting than non-using controls, meaning that they had a stronger preference for more immediate over delayed monetary rewards. By contrast, the study by Acuff et al. [23] showed no differences between cannabis users and controls on the same delay discounting measure. Neither Taylor and Filbey [24] or Petrucci et al. [32•] found that cannabis use was associated with sensitivity to punishment or sensitivity to reward, with the exception of higher fun-seeking and lower sensitivity to punishment on one of two scales in cannabis users compared with controls in the latter study. We also found no differences in risky decision-making between 39 young adults with CUD and 20 controls in another recent study using the Cambridge Gamble Task [44•]. Of note, both this study and the CannTeen study [45] found that cannabis use was associated with poorer visual and verbal episodic memory, respectively, showing that cannabis use be associated with other aspects of cognition even if it is not related to amotivation.

Functional Neuroimaging Research on Cannabis and Reward Processing

The areas of the brain most frequently implicated in reward and motivational processes include the mesolimbic dopamine system and ventral striatum, the anterior cingulate cortex, and the ventromedial prefrontal/orbitofrontal cortex [15, 16, 46, 47]. To measure reward-related brain activity in these areas, most functional magnetic resonance imaging (fMRI) studies to date have used the Monetary Incentive Delay (MID) Task, which includes a reward anticipation phase and a reward feedback phase [48]. These studies have found mixed results on the association between cannabis use and reward-related brain activity, with some finding increased activity or functional connectivity in cannabis users, others finding decreased activity, and some finding no differences between cannabis users and controls [19•]. As previous studies have been highly heterogeneous with respect to how cannabis use has been operationalised and quantified, the age of onset, duration of use, and duration of abstinence in user groups, and the extent to which important confounders (such as nicotine/cigarette use and depression) have been measured, it is difficult to determine whether any of these factors contribute to the variability in findings. Moreover, previous fMRI studies in cannabis users have typically had small samples with consequently low power, which decreases the reliability of individual results.

However, one key study by Martz et al. [49] is worth highlighting, as this was a relatively large and longitudinal study including 108 young adults. In this study, past-year cannabis use predicted attenuated activity in the nucleus accumbens during reward anticipation at future timepoints, though this association was not significant in a cross-sectional baseline analysis. In our own recent cross-sectional study from the CannTeen project, we also found no differences between 63 cannabis users and 62 controls in ventral striatal responses to reward anticipation [50•]. It is unclear why results from cross-sectional and longitudinal investigations differ. It could be that cannabis use is associated with a small attenuation of ventral striatum activity during reward anticipation, but that that pre-existing differences in reward networks between cannabis users and non-users obscure this relationship in cross-sectional studies.

Cannabis has also been found to attenuate reward-related activity in the ventral striatum acutely. In a recent investigation from the acute arm of the CannTeen project, we found that 0.107 mg/kg inhaled THC (e.g., 8 mg for a 75-kg person) attenuated activity in the ventral striatum and insula compared with a placebo during reward anticipation in 47 adult and adolescent weekly cannabis users [51]. Using resting-state fMRI, Wall et al. [52] also found that 8-mg inhaled THC reduced connectivity in the limbic striatum in 17 adult weekly cannabis users compared with a placebo. However, Murray et al. [53] found no effect of 7.5-mg or 15-mg oral THC on anticipatory event-related potentials during an electroencephalography-adapted version of the MID task in 24 adults with ≤ 20 lifetime days of cannabis use, though THC reduced the amplitude of several of components during feedback.

In summary, there is some evidence from both the acute and non-acute literature that cannabis exposure is associated with blunted reward anticipation responses in the ventral striatum. Activity in the ventral striatum during reward anticipation has been found to correlate negatively with anhedonia [54, 55], though it is not clear whether it is related to willingness to expend effort for reward on the EEfRT and similar measures of motivation discussed in this review. Future research is needed to determine whether the ventral striatal reward anticipation response is a clinically relevant and reliable biomarker of behavioural indices of reward and motivation.

Conclusion

In summary, recent findings from the literature on cannabis use and motivation do not harmonise with media portrayals of people who use cannabis as lazy, demotivated, and lacking in ambition. Several studies have found that cannabis users are more willing to expend effort for reward compared with controls. However, it seems that recreational use of cannabis produces different results than dependency on cannabis use. For example, there is some evidence from survey studies supporting an association between apathy and cannabis use dependence or CUD. Similar findings have been shown for some measures of cognition, where cannabis users with high levels of dependence or CUD are significantly different from controls [44•]. A similar effect has been noted in other substances including novel psychoactive substances [56], stimulant users [57], and cocaine users [58]. Therefore, it seems that understanding dose and chronicity of drug use is critical. The acute literature, though sparse, suggests that weekly cannabis users are less willing to expend effort for reward while they are high, which could result in a persistent ‘amotivational state’ if cannabis is used several times daily.

Given this discrepancy between popular belief and the research literature, it would be interesting to see research comparing of self- and observer ratings of motivation in cannabis users. Meier and White [59] have previously found that cannabis users are rated as more apathetic than controls by informants, and it could be that common beliefs about how cannabis affects motivation engender a prejudiced perception of users as less motivated than they actually are. This research should also include assessments of stereotype awareness and threat to explore whether cannabis users’ own awareness of the amotivation stereotype may encourage them to appear more or less motivated in psychological studies.

Importantly, motivation is a multi-faceted concept, encompassing several factors and traits beyond those assessed in the current review. Future research using alternative and ecologically valid measures is needed to comprehensively assess the potential link between motivation and cannabis exposure. Moreover, of the studies investigating willingness to expend effort for monetary reward, only one [23] controlled for participant income. Income and socio-economic status may influence participants’ sensitivity to monetary reward magnitude and should therefore be considered in these studies. In addition, future studies should directly compare cannabis users with and without CUD on motivational outcomes.

Future studies should also maintain a focus on adolescents, as they may be more vulnerable to potentially harmful effects of cannabis compared with adults [37,38,39,40] and ensure that samples are inclusive and representative with respect to race/ethnicity and gender [19•]. Although sex differences in the endocannabinoid system are likely to be small [60], there are a few recent studies which suggest that associations between cannabis use and specific domains of neurocognitive functioning differ in males and females [61, 62]. Studies should account for this possible confounder by ensuring that groups are balanced with respect to sex/gender or by including it as a covariate in statistical models. Finally, tobacco/nicotine use has been shown to influence the association between cannabis use and reward processing [34, 50•, 63] and may have its own effects on the reward system [64, 65]. Therefore, it is crucial that tobacco/nicotine co-use is assessed in future research on cannabis use and motivation.