Background
Cannabis is one of the most commonly used psychoactive substances in the world, with use most prevalent among emerging adults (15–24 year olds) [
1‐
5]. Cannabis use has been associated with negative physical and mental health effects in a dose-response fashion, where near daily or daily use is associated with worse outcomes [
6]. Harmful levels of use have been increasing among emerging adults in Canada [
7,
8] and the United States [
1]. Risks of cannabis-related harm are more pervasive for individuals who begin using cannabis during adolescence, with earlier age of first use potentially resulting in long lasting consequences [
6]. Given the high prevalence of use and potential for significant impairment, efficacious interventions for high-risk individuals in this age group are a pressing clinical priority.
Emerging adults are neurodevelopmentally vulnerable to the effects of cannabis, as cannabis acts on areas of the brain integral to brain development. The brain is not completely matured until approximately 25 years of age [
9]. Chronic, regular cannabis use during adolescence has shown to negatively affect memory, attention, and psychomotor skills [
10‐
12], potentially causing irreversible cognitive impairment [
13] resulting in an increased likelihood of fatal car accidents [
14], poor academic performance [
15‐
17], and dropping out of school [
17] . Additionally, weekly cannabis use or a cannabis use disorder is almost 10 times as likely in people with other mental illness as compared to those without other mental illness [
18]; frequent use has been associated with psychotic disorders [
14,
19], bipolar disorder [
14], personality disorders [
20], depression [
20‐
22], anxiety [
23], and suicidal ideation and attempts [
24]. Overall, cannabis use during emerging adulthood is particularly concerning due to its potential to disrupt neurological, social, emotional, and cognitive development.
Despite the associations between cannabis use and negative health consequences, the perceived risk of using cannabis, both occasionally and regularly, is decreasing among adolescents and emerging adults [
25‐
28] and, subsequently, there has been an increase in social acceptance of cannabis use [
29]. This is further compounded by the perception of high-frequency peer use; in North America, emerging adults perceive that about 86% of their peers are using cannabis at least monthly when only about 20% of students actually report using monthly [
7,
30]. Additionally, for general mental health concerns, less than half of emerging adults in need receive professional help [
31] with common reported barriers to treatment including stigma, embarrassment, problems recognizing symptoms, self-reliance, and importantly, not enough time [
32,
33]. These barriers to seeking general mental health services may be magnified for substance use concerns due to the perception of normalcy of problematic behaviors. Therefore, the perception of low-risk, high peer use, and social acceptance make emerging adults a clinically challenging population, which is further compounded by low motivation for change.
Existing literature on interventions targeting post-secondary substance users acknowledges the challenges to engaging this population and, therefore, has focused on brief interventions (BI) or brief motivational interventions (BMIs). There are many different existing definitions for brief interventions but all contain typical ingredients. BIs typically are short in duration [
34,
35] and include provision of personalized feedback [
36]. Most BIs adopt a motivational interviewing (MI) approach with the primary goal of the BI being to motivate participants to change their behavior, teach behavioral change skills, and connect to services [
35,
37‐
39]. Often, BIs follow the FRAMES model in which the participant receives personalized
feedback, reinforcement of personal
responsibility, objective
advice given non-judgmentally, a
menu of options, an
empathetic and accepting listener, and encouragement of
self-efficacy and confidence [
38‐
40].
Emerging adulthood is a distinct developmental period characterized by instability and exploration, often referred to as extended adolescence, in which individuals typically experience reduced parental monitoring but are not yet fully engaged in the responsibilities and expectations of adulthood [
41]. Emerging adults straddle adolescence and young adulthood, sharing some similarities with both developmental periods. A scoping search was performed to identify the general breadth of existing brief intervention literature to inform the specifics of this review. Existing literature on BIs for cannabis use is already limited, and is particularly scarce when focused on emerging adults. Thus, BIs for adolescents and young adults should also be explored to provide a comprehensive picture and clinical relevance of the existing BI literature.
We identified three reviews on BIs for adolescent substance use. Jensen (2011) looked specifically at MI approaches (including BIs and longer duration interventions, 1 to 9 sessions) for adolescent (12–20 years of age) substance use, finding evidence that suggests MI approaches are helpful to reduce general substance use in the short and longer term (significance retained at follow-up) [
42]. Barnett (2012) conducted a systematic review on MI interventions for adolescent substance use (mean age < 18.5). Although they did not perform a meta-analysis, they indicate that 67% of the studies result in reductions in some form of substance use outcomes, including marijuana use [
43]. A Cochrane review by Carney (2016) found six randomized controlled trials (RCTs) of face-to-face school-based BIs for adolescents (under 19 years of age) who experience negative behavioral consequences from subclinical levels of substance use [
44]. Moderate-quality evidence suggests that effects of BIs on cannabis frequency and dependence are not significantly different compared to information provision (health promotion materials and harm reduction information). However, when comparing BIs to assessment only (evaluated on substance use but received no intervention), BIs appear to reduce cannabis frequency (SMD − 0.54 [− 0.77, − 0.31]), although this is based on low-quality evidence and only includes results from two RCTs (
n = 338).
For emerging adults, we identified one relevant literature review by Dennhardt and colleagues (2013) [
45]. This review found one observational study and five RCTs on BIs and examined their effect on substance use outcomes, including cannabis use. They did not perform a systematic search and did not combine results meta-analytically, but concluded that brief motivational interventions demonstrated the most promising results for college students, apart from parent-based interventions, and requires further investigation.
For adults, there is a Cochrane review by Gates et al. (2016) on psychosocial interventions for cannabis use [
46]. This study found 23 RCTs of psychosocial interventions (which include CBT, MI, mindfulness, counseling or education contingency management, relapse prevention) for adults with cannabis abuse or dependence or near daily users of cannabis who were seeking treatment for their cannabis use or other adults seeking treatment for cannabis use. Results suggest moderate-quality evidence that individuals who receive a psychosocial intervention use cannabis on fewer days compared to inactive control; low-quality evidence that those receiving an intervention were more likely to report point-prevalence abstinence, fewer symptoms of dependence, and fewer cannabis-related problems compared to inactive control; and very low-quality evidence that individuals receiving interventions use fewer joints per day compared with inactive control. Additionally, interventions longer than four sessions for more than a month appear to demonstrate better outcomes and Cognitive Behavioral Therapy (CBT) appears to produce the largest effects followed by motivational approaches.
There are several methodological and conceptual limitations of existing reviews. Methodologically, one study did not including a systematic search [
45], two did not include unpublished literature [
42,
43], and two only included RCTs [
44,
46]. In regards to the interventions, most did not look at BIs (1–2 sessions) neither as a whole or within a subgroup analysis [
42,
43,
46], most were not cannabis specific [
42‐
45], and there were common restrictions based on the delivery location of interventions (i.e., only in secondary school [
44], only in person [
44,
46], no inpatient [
42], only outpatient community [
46]). In the two most comprehensive Cochrane reviews, there were participant restrictions based on baseline substance use; Gates required participants to have a minimum amount of cannabis use at baseline and excluded individuals who regularly used or had a substance dependence on a substance other than marijuana or nicotine [
46] while Carney excluded any individuals who had any substance dependence [
44]. Also, only one review covered a youth population (12–25) and is fraught with other methodologically and conceptual limitations including being outdated [
42]. Additionally, the lack of gold standard BI approach for cannabis use means that there is significant variability in the content and delivery methods of existing BIs. This variability increases heterogeneity and limits our ability to determine the salient components of a successful BI.
This review seeks to address these gaps by (1) focusing primarily on cannabis related outcomes, (2) conducting an up-to-date systematic search of all BIs for cannabis, inclusive of all youth populations and study designs, (3) providing comprehensive descriptions of the contents and delivery methods of existing BIs, and (4) performing multiple subgroup analyses based on content and delivery methods to try to determine the most important and effective components of a BI.