Substance Use Among Youth During the COVID-19 Pandemic: a Systematic Review

Purpose of Review
 To review the literature on the trends in substance use among youth during the coronavirus SARS-CoV-2 (COVID-19) pandemic. Recent Findings The pandemic has given rise to concerns about the mental health and social well-being of youth, including its potential to increase or exacerbate substance use behaviors. This systematic review identified and included 49 studies of use across alcohol, cannabis, tobacco, e-cigarettes/vaping, and other drugs, and unspecified substances. The majority of studies across all categories of youth substance use reported reductions in prevalence, except in the case of other drugs and unspecified drug and substance use, which included three studies that reported an increase in use and three studies that reported decrease in use. Summary Overall, the results of this review suggest that the prevalence of youth substance use has largely declined during the pandemic. Youth substance use in the post-pandemic years will require monitoring and continued surveillance. Supplementary Information The online version contains supplementary material available at 10.1007/s11920-022-01338-z.


Introduction
The adolescent years represent an important developmental stage during which the foundation for future patterns in substance use is often established [1]. Both the quantity and frequency of use during this period are strongly associated with risks for heavy use and misuse of substances in adulthood [2,3]. As an example of the staggering economic and societal costs, substance use in the USA alone has been estimated at over $400 billion annually by the US Surgeon General [4]. In addition to the direct economic impact, the societal harm caused by substance use in the USA has been estimated at over $800 billion annually due to premature death or quality-of-life adjustments [5]. Youth alcohol, tobacco, and other drug use impairs psychological and neurocognitive development and increases risk for academic failure, chronic disease, and mental illness [6,7]. Thus, the prevention of youth substance use remains an important priority for public health globally.
Various domains of established risk and protective factors play an important role in preventing the development of youth substance use. These include access to care and support provided by parents, family, and friends; structure, supervision, and support from school faculty and staff; and access to and participation in pro-social leisure time activities [8,9]. Studies that take an ecologic view of substance use have further assessed the impact of environmental factors known as "context effects," which independently contribute to the odds of alcohol, tobacco, and other drug use among youth. Generally, such studies have found that youth who live under challenging home situations or in resource-limited areas, or both, are more likely than other youth to be negatively affected by sudden environmental changes and thus may turn to substance use as a coping mechanism [10][11][12].

The COVID-19 Pandemic
The novel coronavirus SARS-CoV-2 (COVID-19) was officially declared a pandemic by the World Health Organization (WHO) on March 11, 2020 [13]. Over 400 million confirmed cases and close to 6 million deaths worldwide have been attributed to the virus [14]. Thus, virtually no human on earth has been unaffected by the virus. During this time, entire countries, regions, states, cities, and towns have enacted various laws, rules, and guidelines in their efforts to curb the spread of the virus and its impact on human health. Some of the more drastic mitigation measures have included closing of borders, lockdowns and curfews, or both, in cities and towns; severe limits on social gatherings and assembly (e.g., religious services); restricted access to worksites and entertainment venues and services (e.g., restaurants, theaters, and sports events); and mandates for physical (or social) distancing and wearing face masks. In most places, these efforts have included closing of schools and restriction of services for youth, such as sport clubs and extracurricular programs, and the prohibition of social gatherings [15,16]. Such extreme measures at the societal level are unprecedented in modern times and have not been seen since the influenza pandemic of 1918 [17].
In addition to the social restrictions, the mitigation efforts to curb the spread of the virus have resulted in unintended consequences that have been harmful in the lives of youth [18]. These include disruption of parental (or caregiver) income and associated financial consequences and stunted academic progress due to school closings, remote instruction, and recurring changes in instructional formats. The pandemic has also increased feelings of loneliness among young people because of long-term social isolation and limited opportunities to interact with peers [12]. During this period, inconsistent and poorly planned institutional responses have been reported [19], including a decline in access to harmreduction services and treatment of substance use [20]. In a recent review, Pfefferbaum highlighted the negative psychological effects of the pandemic on children and youth, including the significant increase in the prevalence of clinical depression, suicidal ideation, and anxiety, all of which have the potential to contribute to an increase in substance use behaviors [21].

The Current Study
Given the human and societal costs associated with youth substance use, we sought to critically assess the impact that the COVID-19 pandemic has had on youth substance use. Some recent studies have shown an increase of substance use among youth, particularly vulnerable youth, such as those living in resource-poor areas or under challenging family circumstances [22], while others have found a reduction in substance use despite an overall worsening of mental health status [23••]. However, despite the significance of the pandemic, a wholistic review of research on youth substance use during the era of the COVID-19 pandemic has not been conducted to date. Consequently, the objective of this systematic review was to provide an overview of the most recent research into youth substance use during the period of the COVID-19 pandemic.

Methods
This systematic review sought to examine the prevalence of substance use among adolescents during the COVID-19 pandemic. Following the identification and selection of peerreviewed papers, we examined each relevant paper by country, sample characteristics (type, age, sample size, period of study enrollment), study design, substance use behavior or outcome (type, measurement), and covariates included in the analyses. The Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) was used to guide the design, execution, and reporting of findings for this systematic review. The research question, inclusion criteria, and search terms were defined using the PICO approach (Population, Intervention [or Exposure], Comparator, and Outcome). We identified and used previously published research articles and reviews on substance use during the COVID-19 pandemic to guide the creation of the search terms. The protocol for this systematic review was registered at PROS-PERO (CRD42022311679).

Inclusion and Exclusion Criteria
Studies were selected based on the following criteria: (1) examined the substance use among youth during the COVID-19 pandemic; (2) study participants were 24 years old or younger; and (3) the study was published in the English language. Cross-sectional and longitudinal studies were included. When two manuscripts presented findings from non-independent datasets, the manuscript with the larger number of study participants was included. Articles were excluded if either COVID-19 (or a related term: COVID pandemic, Coronavirus, etc.) or substance use (or related terms: substance abuse, addiction, alcohol, nicotine, smoking, vaping, tobacco, licit drug/s, illicit drug/s, drug/s, etc.) was not identified in the paper's title or abstract.

Identification of Studies
All databases within Web of Science were used in conducting the search. The search was limited to studies published on, or subsequent to, the date the COVID-19 pandemic began (December 1, 2019) to studies published up to February 15, 2022. Thus, the last search for this review was conducted on February 15, 2022. Titles, abstracts, and articles were reviewed to identify potentially relevant manuscripts. The search terms included combinations of COVID, adolescent*, child*, youth, substance use, substance abuse, drug, substance drug, smoking, tobacco use (Table 1). Reference lists of included research studies and published reviews of substance use among youth during the COVID-19 pandemic were also searched.

Data Extraction
The initial search based on the inclusion and exclusion criteria was performed by one investigator (HL) and then repeated by a second investigator (IET) to ensure that all relevant articles were included. The investigators conducting the search were located across two different countries (the USA and Iceland) with access to different research databases. As such, the second investigator's search yielded an additional 17 studies that were not included in the first search. These discrepancies in the search findings from the two investigators who performed the search were discussed and a consensus was reached by the two investigators. Key elements of relevance for this review were extracted from each paper, summarized, and entered into an Excel spreadsheet, which was used to inform the broader discussion of the current state of the literature among the collaborating authors.

Results
The initial search yielded 423 articles of potential interest. Of those, 49 articles met full eligibility criteria (see Fig. 1 for PRISMA flow chart). Five articles were published in 2020, 38 in 2021, and 6 in 2022. Forty-six articles from 23 countries reported on studies conducted with singlecountry samples and three articles reported on studies from multiple countries. Most of the studies were conducted in North America (n = 22) or Europe (n = 19). Twenty-nine articles reported studies that were based on cross-sectional designs and 20 on longitudinal designs. Forty-four articles reported on participant samples of between 10 and 25 years of age, and five articles also included older individuals. Regarding outcomes, 14 articles reported studies with a single substance use outcome, 29 articles included multiple substance use outcomes, five articles reported on general substance use without specifying type of substance, and one article focused solely on substance abuse disorder. Below, we have organized the summaries of our findings from the review of the 49 articles by substance use outcome ( Table 2). Articles reporting on multiple substance use outcomes are included in multiple summaries based on the respective outcome.

Discussion
The COVID-19 pandemic and associated social restrictions implemented to contain the spread of the virus have led to concerns from parents, educators, and healthcare professionals and researchers about what effects the pandemic may have had on the mental health and social well-being of youth. To partially address this concern, the objective of this systematic review was to examine the prevalence of youth substance use during the COVID-19 pandemic. Based on 49 studies published to date and captured in our search, the overall results of our review suggest that the prevalence of youth alcohol, cannabis, tobacco, and e-cigarette/vaping use has declined during the pandemic.
This finding of an overall decline in the prevalence of substance use during the pandemic is certainly positive, but it begs the question: To what can the decrease be attributed? Youth substance use most often takes place outside the home environment and usually within the context of the peer group. Moreover, youth substance use is highly dependent on availability and access to drugs and other substances. The public health restrictions that were necessary during the COVID-19 pandemic limited the time most adolescents spent in-person with their peers, and it follows that availability and access to alcohol, tobacco, and other substances was effectively limited during community lockdowns. In short, young people confined to their homes with parents had fewer opportunities for accessing and using substances. Thus, limited peer-group gatherings, decreased availability and access to substances, and increased time spent in the home with parents-all wellestablished factors shown to be effective in prevention efforts aimed at decreasing substance use [71]-are likely to have conferred important protection against substance use during COVID-19 as observed in the decline in prevalence reported across the bulk of studies we reviewed.
These promising and positive findings of an overall decrease in substance use, however, need to be viewed with some caution. First, some groups of youth may have had more pre-pandemic vulnerability to substance use during the pandemic for several reasons. For instance, there is evidence that mental health problems have been on the rise among many adolescents prior to and during the pandemic. In addition, for older adolescents and young adults experiencing increased stress and mental health problems, there is evidence that alcohol, drugs, and other substances may have offered a coping mechanism during the pandemic [12]. Youth that used substances by themselves, moreover, had increased symptoms of depression [28].
Spending more time in the household is not always a consistent protective factor. One study found that youth were drinking and using other substances with their parents shortly after social distancing measures were imposed, suggesting that permissive parental attitudes and behaviors could encourage and facilitate youth alcohol consumption and other substance use [72]. These permissive attitudes and modelling of health compromising behavior can influence the perceived norms towards substance use, resulting in increased use after the pandemic. Moreover, adolescents living with family conflict or dysfunction are more likely to engage in substance use [73]. One systematic review of 32 reports [74] found evidence that domestic violence has increased during the pandemic, indicating that the at-risk group of youth living with family conflict and dysfunction increased during this time. Finally, in addition, youth living under the stress of parental substance use, family dysfunction, and domestic violence could predispose the later onset of substance use and violent behavior. Youth who missed out on "normal teenage years" or important rites of passage that were interrupted by the pandemic may also have difficulties with substance use later in life when restrictions are removed, and social gatherings allowed. What this means for the prevalence of substance use in the post-pandemic years will require monitoring and further surveillance. Thus, the long-term effects of the pandemic and its potential dormant or latent effects on responsible adult substance use are unknown at this time and not likely to be fully understood until years later.

Implications for Prevention and Treatment
Although the findings of our review suggest that the various mitigation strategies to contain the spread of COVID-19masking, physical distancing, and community lockdowns that imposed restrictions on social gatherings-may have had detrimental impact on the mental health and social well-being of youth [21], such measures did not necessarily lead or contribute to an increase in youth substance use. Notwithstanding, there are several implications for prevention and treatment that should be considered in the aftermath of this pandemic. First, focusing on improving adolescent mental health should be a priority. Poor mental health is a well-known risk factor for substance use and misuse and the majority of young people with substance use problems suffer from co-occurring mental health issues that are often difficult to treat [75,76]. Second, although remote learning enabled young people to maintain some connection to schooling, studies have pointed to the negative impact of virtual learning on the academic and social development of many young people and thus may have set the stage for a "lost generation" of youth who could be at even greater risk for substance use in the future [19]. Post-pandemic efforts undoubtedly will need to address the gaps in academic and social development of this cohort of young people-especially those for whom there have been significant disparities in access to educational opportunities. This suggests that community-wide surveillance and prevention of substance use needs to become a greater community priority than prior to the pandemic. Third, COVID-19 has demonstrated both the value of e-health and telemedicine to address the health needs of people during the pandemic [77]. However, the limited availability and access to mental health counseling and other forms of virtual treatment during the early phases of the COVID-19 pandemic may have contributed to placing young people at greater risk for substance use. As such, greater investment in e-health treatment for mental health problems and referral should be a greater priority in the future.

Limitations
The findings of this review should be viewed with some caution because of design and other methodological limitations of the studies we reviewed. First, most of the published studies we reviewed utilized cross-sectional designs and focused largely on prevalence of use; few studies utilized longitudinal designs, outcome measures varied, and any follow-up was of limited time duration. Second, many studies used non-probability sampling methods to identify and obtain participants, including convenience, purposive, or volunteer samples, all of which limit the external validity of their findings. Third, few studies reported analyses that examined differences by gender. This remains an important question for future research because of the gender differences that have been observed in substance use and mental health outcomes during the COVID-19 pandemic [23••]. Finally, most of the studies reviewed included investigations of substance use of a single category, rather than across multiple categories of substance use, thus precluding analysis of any synergistic or gateway effects of multiple drug use for which the pandemic may have been responsible.

Recommendations for Future Research
Our review suggests several directions for future investigation. First, numerous studies have now documented the impact of COVID-19 on the lives and well-being of adolescents in the immediate aftermath of the pandemic; however, more longitudinal studies are needed to assess the latent and long-term effect of the pandemic on substance use behaviors among youth. Although the pandemic may not have fostered increased substance use among most young people, further investigation is needed to understand differential risk across high-risk adolescents and differences by gender during the pandemic. In addition, more attention should be given to the role of key covariates in understanding youth substance use. For example, covariates such as socioeconomic status and social determinants of mental health should be addressed in research that seeks to understand the relationship of substance use to youth mental health and social well-being. Finally, as more studies are published, meta-analyses of youth substance use during and following the pandemic will be possible and are needed to better understand how and to what extent the pandemic influenced substance use and any underlying causal mechanisms.

Conclusions
This systematic review of youth substance use during the COVID-19 pandemic assessed studies across several categories of substances, including alcohol, cannabis, tobacco, e-cigarette/vaping, and use of other drugs and unspecified substances. Regardless of the type of substance use, we found little evidence across the 49 studies we reviewed that the prevalence of use increased in response to the potential social and emotional deprivations associated with the pandemic. In fact, apart from some increase in the use of unspecified drugs or other substances, the majority of studies reported reductions in use across alcohol, cannabis, and tobacco and related products. Thus, we conclude that the bulk of the available evidence suggests that the prevalence of youth substance use largely declined during the first 2 years of the pandemic. gram, which is based on the Icelandic Prevention Model, from which they receive salary or consulting fees; all other authors disclose no financial or non-financial interests that are directly or indirectly related to the work submitted for publication.
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