Studies on the short- and long-term effects of combined binge drinking (BD) and cannabis consumption on academic performance in university students are underrepresented (Arria et al., 2013; Meda et al., 2017) even though academic performance is known to act as a barometer for educational success or ineffectiveness and as a key predictor of the prospects of young adults (Jalaliyoon and Taherdoost, 2012). The lack of relevant studies is especially surprising if we consider that the co-use of legal and illegal drugs in the university population has increased substantially in Western countries in the last decade (Substance Abuse and Mental Health Services Administration, 2020).

The sociocultural, economic, and demographic context of our time, together with the academic standards prevailing in Western universities, has in recent decades generated a system that requires students to assume greater autonomy in decision making and a higher level of competitiveness that today largely depends on their ability to work with information (Staff et al., 2010). University students find themselves at the emerging adulthood stage (Arnett and Jensen, 2000). This is an intermediate developmental stage, situated between adolescence and adulthood proper, characterized by identity discovery, uncertainty about sexual beliefs, evaluation of different options and decisions about priorities in a gradual and responsible way. It is also a period in which the students must balance their responsibilities to their parents with their desire for freedom from social roles and normative expectations in an unknown and highly competitive environment (Arnett, 2006; Arnett et al., 2011; Peer and McAuslan, 2016; Scales et al., 2016). In this context of uncertainty and identity confusion together with permissive policies (Vitale, 2014; Bolin et al., 2017; De Faria et al., 2021), peer pressure, and low risk perception (Schulenberg et al., 2017), some risk behaviors such as substance use, are clearly increasing (Johnston et al., 2009; Skidmore et al., 2016; Allen et al., 2017; Gómez et al., 2017; Holloway and Bennett, 2018; Welsh et al., 2019; Jackson et al., 2020).

Access to university is no longer a protective factor for many students (Schulenberg and Maggs, 2002; Sarokhani et al., 2013; Eskin et al., 2016; Ribeiro et al., 2018; Arria et al., 2020; Thompson et al., 2021). Although the transition to university is not a homogeneous experience (Mayhew et al., 2005; Fierro Arias and Moreno Hernández, 2007; Coertjens et al., 2017), students generally face constant demands of academic, personal, emotional, and social adjustment for which they are not always prepared (Baker and Siryk, 1989; Harvey et al., 2006; Credé and Niehorster, 2012). University adjustment is more than a score on a standardized test, and it involves facing multiple stressors that make the initial entry period particularly difficult time, which can lead to high levels of anxiety, interpersonal conflicts, feelings of isolation and loneliness, constant feelings of being overwhelmed, poor adaptation, academic failure and attrition (Abdullah et al., 2009; Aspelmeier et al., 2012; Clinciu, 2013; Bailey and Phillips, 2016; Rodríguez et al., 2017; Sharp and Theiler, 2018; Pascoe et al., 2020; Raza et al., 2021). Students face a myriad of challenges during their transition to university, including developmental changes, which make them particularly vulnerable to substance abuse during this period (Staff et al., 2010; Derefinko et al., 2016). BD and cannabis consumption some of the most influential risk factors (Wechsler et al., 2002; Caldeira et al., 2008; Arria et al., 2015; Subbaraman and Kerr, 2015; Hayaki et al., 2016; Merrill and Carey, 2016; O’Hara et al., 2016; Gómez et al., 2017; Johnson et al., 2017; Meda et al., 2017; Busto Miramontes et al., 2019; Mallett et al., 2019). The national survey on drugs in Spain (Substance Abuse and Mental Health Services Administration, 2020) reports frequency of BD in the population aged between 14 and 18 years of 32.3%, that almost half of this population are cannabis users (OEDA, 2019).

Aside from impairing overall health (Simons et al., 2005; Hall and Degenhardt, 2009; Keith et al., 2015) and well-being (Liu et al., 2019), prior cross-sectional (Aertgeerts and Buntinx, 2002; Wolaver, 2002; El Ansari et al., 2013; Liguori and Lonbaken, 2015; Piazza-Gardner et al., 2016; Bolin et al., 2017; Tembo et al., 2017; Hernández-Serrano et al., 2018; Páramo et al., 2020) and longitudinal (Arria et al., 2013, 2015; Suerken et al., 2016; Meda et al., 2017; Patte et al., 2017) research has found that students who partake in binge drinking and cannabis use, either together or separately, spend less time studying, miss more classes, are less academically motivated, obtain lower grade point averages (GPAs), and also have an elevated risk of university attrition. Previous data obtained by our research group (Páramo et al., 2020) in a cohort of Spanish first-year university students classified as binge drinking and cannabis users have shown that academic adjustment mediates the effects of BD and cannabis on academic performance. The study demonstrated the importance of poor academic adjustment as a risk factor for academic performance.

The impact of both BD and cannabis consumption on academic performance is associated with adverse effects on cognitive functions such as inhibitory control (López-Caneda et al., 2014), impairments in memory, particularly verbal and working memory (Solowij and Battisti, 2008; Deniel et al., 2021; Morie et al., 2021), attentional deficits, and poorer processing speed (Crean et al., 2011; Jacobus et al., 2015; Gil-Hernandez et al., 2017; Carbia et al., 2018).

The effects of combined BD and cannabis consumption on academic performance and adjustment in university students have mainly been examined in cross-sectional studies and it is difficult to observed changes in different cohorts. Most of the few longitudinal studies reported in the above-mentioned literature have been carried out in the USA. To the best of our knowledge, there are no follow-up studies with data obtained at two time points and that analyze the impact of combined BD and cannabis consumption on academic performance and adjustment in Spanish university students. Therefore, the primary goal of the present study was to follow-up the effects of combined BD and cannabis consumption in first-year students on academic performance and adjustment after 2 years of undergraduate study. The second goal was to analyze the mediating role of academic adjustment on the relationship between combined BD /cannabis consumption and GPA. The final goal was to analyze whether, after controlling for T1 academic adjustment and GPA, the effects of co-consumption on academic performance are maintained. Based on previous findings, it was hypothesized that: (1) BD and cannabis co-consumption would be associated with poorer long-term GPA; (2) BD and cannabis co-consumption would be associated with poorer long-term university adjustment; and (3) we expected that the academic adjustment will mediate the relationship between BD and cannabis co-consumption and GPA, once controlled the effect of academic adjustment and baseline grade point average.

The time spent at university is a unique opportunity for the intellectual and social growth of student, but it is also a time of high-risk due to exposure to multiple addictive substances with important repercussions for educational aspects and public health (Caldeira et al., 2008; Schulenberg et al., 2017). Existing research on this topic has relied heavily on cross-sectional designs and has mainly focused on the effects of the use of a single psychoactive substance in first-year undergraduates (Aertgeerts and Buntinx, 2002; Liguori and Lonbaken, 2015; Piazza-Gardner et al., 2016). Few studies have used longitudinal designs focused on the simultaneous use of alcohol and cannabis in the university population. This prospective follow-up study helps to improve our knowledge of how consumption of substances may affect academic adjustment and success in Spanish university students. The study findings confirmed the hypothesized association between BD and cannabis co-consumption and poorer academic performance. Our results revealed that the first-year students included in the BDCA group exhibited poorer academic performance in the third year. The interdependent relationship between alcohol and cannabis co-consumption and academic performance documented herein confirms previous findings in cross-sectional (El Ansari et al., 2013; Tembo et al., 2017; Hernández-Serrano et al., 2018; Parisi et al., 2019) and longitudinal (Arria et al., 2015; Suerken et al., 2016; Meda et al., 2017) studies. Thus, the research findings clearly show that poor academic performance is associated with BD and cannabis consumption, whether combined or separate. In one of the few longitudinal studies of this relationship, Meda et al. (2017) found that students who use both substances at moderate to high levels obtained significantly lower grades both at baseline and across the 2 years of research. These results are consistent with those of Arria et al.’s (2015) and Suerken et al.’s (2016), who reported that frequent marijuana use during the first year at college is associated with an increased risk of not completing college or of delayed graduation. The incidence of BD and cannabis use during young adulthood has been associated with to long-lasting neurocognitive alterations (Jackson et al., 2020; Lees et al., 2021). Previous studies have demonstrated that BD and cannabis consumers have poor executive functions and display difficulties in demanding working memory (WM) tasks that require self-monitoring of information (López-Caneda et al., 2014; Gil-Hernandez et al., 2017; Meruelo et al., 2017; Yurasek et al., 2017; Carbia et al., 2018; Deniel et al., 2021). Such deficits can lead to lower academic motivation, poorer study skills, skipping class and disrupted attendance (Arria et al., 2013, 2015).

The second hypothesis was partially confirmed. Consistent with baseline findings (Páramo et al., 2020), the results show that combined BD and cannabis consumption adversely affects academic adjustment. Specifically, we found that academic adjustment was significantly lower in the BDCA group than in control group. BDCA students displayed greater difficulties in dealing with educational demands, such as lower motivation to complete academic tasks, lower academic effort, and greater levels of dissatisfaction with the academic environment. This finding is consistent with those of previous studies (Arria et al., 2013, 2015; Subbaraman and Kerr, 2015; Skidmore et al., 2016; Meda et al., 2017; Jackson et al., 2020), which revealed that, as students who sustained co-consumption tended to experience a decline in their motivation to manage the educational demands of the university experience. It is possible that this low motivation to cope with new academic demands and the greater dissatisfaction with the academic environment may explain the poorer quality of academic adjustment compared to that of non-consumer students. Nevertheless, given that the association between co-consumption and variations in academic adjustment over time in the university population has scarcely been explored, further research is needed before robust conclusions can be drawn.

Another important finding of this study is related to the different developmental pattern in the personal- emotional adjustment dimension. In our first study, we found no differences in this dimension between the BDCA group and the control group. However, in the third year the BDCA group showed poorer personal-emotional adjustment than the students in the control group. As this finding shows, the effect of co-consumption not only interferes at the academic level, but also in the way of experiencing general psychological distress in coping with the demanding requirements of university life. Co-consumption of substances may have cumulative effects and different long-term trajectories (Zucker, 2006; Staff et al., 2010; Arria et al., 2013; Meda et al., 2017; Schulenberg et al., 2017). One possible explanation, similarly to that given in previous studies (e.g., Simons et al., 2005; Hall and Degenhardt, 2009; Keith et al., 2015; Skidmore et al., 2016; Pascoe et al., 2020; De Faria et al., 2021) is that drug use in university students is related to higher levels of avoidance coping, which is related, in turn, to poor sleep quality, poorer well-being, higher perceived stress, irritability and increased symptoms of depression. It is important to note that very few prospective longitudinal studies have focused on understanding the association between co-consumption and personal- emotional adjustment in university students.

Finally, in line with our third hypothesis, the present findings extend our prior research of this cohort sample on the mediating role of academic adjustment in the relationship between combined binge drinking/ cannabis consumption and GPA by the end of the first year of college (Páramo et al., 2020). Academic adjustment remains one of the mechanisms driving the effects of co-consumption on achievement. After 2 years of undergraduate study, the ratio of indirect to total effect (64.61%) was higher than that observed in the first year (34.33%). Furthermore, we also confirmed that the mediating effect of academic adjustment was maintained after controlling for academic adjustment and GPA baseline (T1). Despite the difficulties in explaining academic achievement in co-consumers based on academic adjustment, previous longitudinal (e.g., Wintre et al., 2006) and cross-sectional studies (e.g., Abdullah et al., 2009; Rodríguez et al., 2017; Raza et al., 2021) the already mentioned meta-analysis of 237 studies by Credé and Niehorster (2012) identified academic adjustment as a powerful predictor of university outcomes, or as a mediator of the relationship between drinking motives and alcohol consequences (LaBrie et al., 2012).

The findings of this prospective follow-up study help to advance our knowledge of how co-consumption of substances may affect academic adjustment and achievement in Spanish university students. The results revealed that first year students included in the BDCA group subsequently showed poorer academic adjustment and performance in the third year at university. The effect of co-consumption interferes not only at the academic level but can also lead to general psychological distress in coping with the demanding requirements of university life. We found that in the third year, the BDCA group showed poorer personal-emotional adjustment than the students in the control group. Finally, academic adjustment proved to be one of the mechanisms driving the effects of co-consumption on academic achievement. Overall, the results of this study should encourage health professionals, educational psychologists, and academic institutions to take ownership of the need for support and involvement in prevention, and for provision of guidelines for implementing appropriate intervention strategies.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving humans were approved by Comité Bioético de la Universidad de Santiago de Compostela. The studies were conducted in accordance with the local legislation and institutional requirements. The ethics committee/institutional review board waived the requirement of written informed consent for participation from the participants or the participants’ legal guardians/next of kin because all participants were of legal age.

MP and MR: conceived and designed study. MP: writing—original draft preparation. MR: designed and analyzed the data. FC: revised the manuscript and funding acquisition. All authors contributed to the article and approved the submitted version.

This work was supported by grants from the Spanish Ministerio de Sanidad, Servicios Sociales e Igualdad, Plan Nacional sobre Drogas (PNSD 2015/034), Ministerio de Economı́a y Competitividad (PSI2015-70525-P) co-funded for European Regional Development Fund, Ministerio de Ciencia e Innovación (PID2020-113487RB-100) and Xunta de Galicia (GRC ED431C 2017/06; ED431C 2021/08).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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