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. Author manuscript; available in PMC: 2022 Oct 1.
Published in final edited form as: Subst Use Misuse. 2021 Oct 1;56(14):2269–2274. doi: 10.1080/10826084.2021.1981390

The Prospective Effects of Parents’ and Friends’ Approval of Drinking on Simultaneous Alcohol and Marijuana Use During College

Bradley M Trager a,1,*, Ashley N Linden-Carmichael b, Reed M Morgan c, Kimberly A Mallett b, Rob Turrisi a,b, Joseph LaBrie c
PMCID: PMC8742524  NIHMSID: NIHMS1761144  PMID: 34596009

Abstract

Recent reports indicate that simultaneous alcohol and marijuana (SAM) use is a growing health concern among college students. As SAM use consists of both alcohol and marijuana, risk factors associated with either can serve as plausible targets by prevention efforts to reduce SAM use. To explore this, the current study investigated the direct and indirect effects of two established risk factors for drinking on SAM use: perceived parental permissiveness toward drinking and friends’ approval toward drinking (injunctive norms). Incoming first-year students (N=470) reported parental permissiveness, injunctive norms, alcohol use, and SAM use at baseline (T1) and 5 months later (T2). SAM use was assessed again 15 months post-baseline (T3). Path analysis was conducted to examine whether T2 variables mediated relationships between T1 variables and T3 SAM use. Results revealed that T2 student alcohol use mediated the effects of T1 parental permissiveness, injunctive norms, and alcohol use on T3 SAM use. Findings from this study extend research on SAM use by identifying perceived parental permissiveness and injunctive drinking norms as risk factors for SAM use through their effects on alcohol use. Based on these findings, it is plausible that parent-based interventions and interventions targeting peer injunctive norms during the first year of college could be used to effectively prevent or reduce SAM use.

Keywords: simultaneous alcohol and marijuana use, college, parental permissiveness, injunctive drinking norms

Introduction

Approximately one in five 18- to 20-year-olds engaged in simultaneous alcohol and marijuana (SAM) use—the use of both substances such that their effects overlap—in the past year (Patrick et al., 2019). SAM use is commonly linked with numerous negative consequences including psychological impairments (e.g., confusion, dizziness; Lee et al., 2017), blackouts, and driving under the influence relative to alcohol- or marijuana-only use (Jackson et al., 2020; Patrick et al., 2021; Subbaraman & Kerr, 2015; for contradictory results, see Mallett, Turrisi, Trager, et al., 2019). As more states move to legalize marijuana, the prevalence of SAM use is likely to continue its historical increase (Hasin et al., 2015; Schulenberg et al., 2019; Terry-McElrath & Patrick, 2018). The first year of college is an especially risky time for alcohol and marijuana use with long-term implications as frequent binge drinking and marijuana use during the first year predicts delayed college graduation and lower income (Wilhite et al., 2017). Thus, there is a need to identify malleable constructs that can be targeted to prevent SAM use (e.g., norms; Linden-Carmichael et al., 2019; White et al., 2019) during the first year of college.

Because SAM use involves the use of two substances, factors that can be targeted to reduce alcohol and/or marijuana use in interventions might also mitigate the frequency of SAM use. If certain drinking-related risk factors were found to influence SAM use, existing interventions targeting those risk factors could reduce SAM use as well. This could eliminate the need for researchers to develop costly new interventions specifically targeting SAM use. Previous research suggests that combining interventions that target both perceived drinking norms and parents’ alcohol-related parenting strategies (e.g., permissiveness toward drinking, hereafter referred to as permissiveness) can effectively reduce alcohol (Mallett et al., 2010; Turrisi et al., 2009) and marijuana use during the first year of college (Grossbard et al., 2010). In non-intervention studies, drinking norms have been found to predict alcohol use (e.g., Collins & Spelman, 2013; Krieger et al., 2016) and SAM use (Linden-Carmichael et al., 2019; also see White et al., 2019). Higher permissiveness has also been shown to predict individual and peer alcohol use in college students (Mallett, Turrisi, Reavy, et al., 2019), and marijuana use in adolescents (Koning et al., 2020) and young adults (Van Ryzin et al., 2012). These studies suggest that SAM use is likely to be associated with having parents who are more permissive and friends who are more approving toward drinking. To identify potential intervention targets to reduce SAM use, the current study examined the direct and indirect influences of these modifiable drinking-related risk factors on SAM use during college. Determining whether these risk factors can affect SAM use would suggest that already existing college drinking interventions may help to reduce this behavior, obviating the resource- and time-intensive development of new SAM use-specific interventions.

Current Study

This study examined the prospective effects of perceived parent permissiveness and injunctive drinking norms during the transition to college on subsequent SAM use. Data were collected at three timepoints: pre-college matriculation (T1) and 5 (T2) and 15 months (T3) following T1. SAM use frequency was reported at all three times, and all other variables were assessed at T1 and T2 (permissiveness, injunctive norms, and alcohol use). Permissiveness, injunctive norms, and participants’ alcohol use at T1 were expected to predict increases in student alcohol use and SAM use at T2 and T3. Associations between heavier drinking and SAM use (Patrick et al., 2018, 2019; Terry-McElrath et al., 2013), permissiveness (e.g., Mallett, Turrisi, Reavy, et al., 2019) and injunctive norms (e.g., Collins & Spelman, 2013; Krieger et al., 2016) in previous studies also suggest that drinking mediates the effects of permissiveness and drinking norms on SAM use. Thus, the current study also examined T2 student alcohol use as a mediator of T1 permissiveness and drinking norms on T3 SAM use (see Figure 1).

Figure 1.

Figure 1.

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Heuristic model depicting pathways between T1 predictors (parent permissiveness toward alcohol, perceived friends’ approval toward drinking, student alcohol use, simultaneous alcohol and marijuana [SAM] use) on T2 mediators (permissiveness, α1–4; friends’ approval, α5–8; alcohol use, α9–12; SAM use, α13–16), and pathways from T2 mediators (permissiveness, β1; friends’ approval, β2; alcohol use, β3; SAM use, β4) to T3 SAM use. Solid lines highlight the hypothesized indirect pathways through which T1 predictors are expected to influence T3 SAM use. Not depicted in the figure, but included in the model, are direct pathways from T1 predictors to T3 SAM use.

Method

Participants

The sample consisted of college students (N=470; Mage=17.9, SDage=0.32) from a large, public university in the Northeast who participated in the control arm of a trial intervention (see Turrisi et al., 2013). Demographic characteristics of the sample were as follows: 54.9% female; 93.6% non-Hispanic; 86.4% White/Caucasian; 4.5% Asian; 3.0% Black/African American; 6.1% multiracial/other.

Recruitment and Procedures

Two cohorts of incoming first-year students were randomly selected from the study institution’s registrar database and mailed invitations to take part in this IRB-approved study (June-July 2007 [Cohort 1] and 2008 [Cohort 2]). The invitation included the purpose of the study, procedures, compensation, study URL, and a personal identification number used to access the online survey. Participants were emailed invitations to complete two follow-up surveys approximately 5 months (T2) and 15 months (T3) after baseline.

Participants received $25 for completing the baseline assessment and $30 for completing each follow-up survey. Participation rates were approximately 86% at T2 and 80% at T3. Baseline SAM use was not found to be significantly different between students who did and those who did not participate in T2 (t(468)=1.12, p=.26) or T3 (t(468)=0.29, p=.77).

Measures

Permissiveness Toward Drinking

Eight indicators adapted from previous studies (Abar et al., 2009; Varvil-Weld et al., 2013; Wood et al., 2004) were used to create latent variables to approximate perceived parental permissiveness toward drinking at T1 and T2: My [mother/father] thinks it is okay if I drink alcohol on special occasions outside the home (e.g., at a friend’s party); My [mother/father] doesn’t mind if I drink alcohol once in a while; How would your parents respond if they knew you drank [one or two/three or four/five or more] drinks on one occasion; How would your parents respond if they knew you drank five or more drinks once or twice each weekend. Response options for all eight items were on a 5-point scale. Items 1–4 were on a scale from Strongly disagree (−2) to Strongly agree (2); items 5–8 were on a scale from Strongly disapprove (−2) to Strongly approve (2). The alpha for permissiveness was .88 at T1 (M=−0.92, SD=0.56) and .91 at T2 (M=−0.67, SD=0.53).

Friends’ Approval Toward Drinking

Four indicators adapted from previous studies (Abar, 2010; Turrisi et al., 2001) were used to create latent variables approximating friends’ approval toward drinking at T1 and T2: My friends would feel favorable toward going to a party on Friday or Saturday night and getting drunk; My friends would feel favorable toward going to a school sponsored event (e.g., football game) on a Friday or Saturday and getting drunk; My friends would feel favorable toward going to a campus special event on a Friday or Saturday night and getting drunk; My friends would feel favorable toward “hanging out” on a Friday or Saturday night and getting drunk. Response options were on a 5-point scale that ranged from Strongly disagree (1) to Strongly agree (5). Alphas for friends’ approval toward drinking at T1 (M=−0.14, SD=0.37) and T2 (M=0.06, SD=0.41) were both .90.

Student Alcohol Use

Student alcohol use in the past 30 days was assessed using three indicators: typical weekly drinking (Daily Drinking Questionnaire; Collins et al., 1985), heaviest drinking occasion, and the number of times they had gotten drunk or very high from alcohol (Dimeff et al., 1999). These measures were then used to create a latent variable of student alcohol use at T1 (M=3.17, SD=1.83) and T2 (M=5.11, SD=3.59).

Simultaneous Alcohol and Marijuana Use

SAM use was assessed with a single item: Please indicate how many times you used marijuana during the past 30 days along with alcohol – that is, so that their effects overlapped? (Miech et al., 2017; Patrick et al., 2018). Response options were on a 5-point scale from Not at all (0) to Every time (4) (T1: M=0.20, SD=0.62; T2: M=0.23, SD=0.64; T3: M=0.37, SD=0.87). 25.5% of the current sample reported any SAM use during the study. Among drinkers, 34.6% reported any SAM use.

Analytic Plan

Path analysis was conducted in Mplus version 7. As illustrated in Figure 1, T3 outcome (SAM use) was regressed onto T2 mediators (β1–4): perceived permissiveness (β1); friends’ approval toward drinking (β2); and student alcohol (β3) and SAM use (β4), and T2 mediators were regressed onto T1 predictors (α1–16). The model was estimated using bootstrapped samples (bootstrap N=5000) to produce 95% confidence intervals (CIs) around the parameter estimates. The test of joint significance (MacKinnon et al., 2002) was used to examine significant mediation effects. Evidence for significant mediation is determined by examining the effects of both the predictor to mediator path (α), and the mediator and outcome path (β). The mediation effect is considered statistically significant if both pathways are significant (p<.05).

An alternate strategy to address the analytic question would be to use a binomial option for the SAM use variable. However, we opted to not use this approach because the analytic demands of the binomial option are a challenge (e.g., Muthén, 2014) and the binomial option would only affect SAM use paths. Further, the bootstrapped approach has the added benefit of asymmetrical confidence intervals for all paths in the model and addresses non-normality as well as skewness.

Results

Regression coefficients (b) and standard errors (SE) from the path model are provided in Table 1. As expected, results revealed that T1 permissiveness (α9: 95% CI[0.25, 1.42]), friends’ approval toward drinking (α10: 95% CI[0.22, 1.02]), and alcohol use (α11: 95% CI[0.40, 0.75]) predicted significant increases in T2 alcohol use, which, in turn, predicted increases in SAM use at T3 (β3: 95% CI[0.01, 0.10]). According to the test of joint significance, T2 alcohol use significantly mediated the effects of T1 permissiveness (α9β3: 95% CI[0.004, 0.11]), friends’ approval toward drinking (α10β3: 95% CI[0.01, 0.08]), and alcohol use (α11β3: 95% CI[0.01, 0.06]) on T3 SAM use. T2 SAM use was also found to mediate the effects of T1 SAM use on T3 SAM use (α16β4: 95% CI[0.03, 0.23]).

Table 1.

Results from path model

Predictor Predictor effect on PTD T2 as mediator (α paths) Mediator effect of PTD T2 on SAM T3 (β1 path) Mediated effect (αβ)
T1 b SE b SE b SE
Permissiveness α 1 0.86 * 0.08 β 1 0.00 0.08 α 1 β 1 0.00 0.07
Friends’ Approval α 2 0.13 * 0.05 β 1 0.00 0.08 α 2 β 1 0.00 0.01
Alcohol Use α 3 −0.001 0.02 β 1 0.00 0.08 α 3 β 1 0.00 0.001
SAM α 4 −0.11 0.07 β 1 0.00 0.08 α 4 β 1 0.00 0.01
Predictor Predictor effect on Friends’ Approval T2 as mediator (α paths) Mediator effect of Friends’ Approval T2 on SAM T3 (β2 path) Mediated effect (αβ)
T1 b SE b SE b SE
Permissiveness α 5 −0.01 0.09 β 2 0.03 0.04 α 5 β 2 0.00 0.01
Friends’ Approval α 6 0.47 * 0.07 β 2 0.03 0.04 α 6 β 2 0.01 0.02
Alcohol Use α 7 0.09 * 0.03 β 2 0.03 0.04 α 7 β 2 0.003 0.004
SAM α 8 −0.14 0.07 β 2 0.03 0.04 α 8 β 2 −0.004 0.01
Predictor Predictor effect on Alcohol Use T2 as mediator (α paths) Mediator effect of Alcohol Use T2 on SAM T3 (β3 path) Mediated effect (αβ)
T1 b SE b SE b SE
Permissiveness α 9 0.81 * 0.30 β 3 0.06 * 0.02 α 9 β 3 0.05 * 0.03
Friends’ Approval α 10 0.63 * 0.20 β 3 0.06 * 0.02 α 10 β 3 0.04 * 0.02
Alcohol Use α 11 0.56 * 0.09 β 3 0.06 * 0.02 α 11 β 3 0.03 * 0.01
SAM α 12 0.07 0.40 β 3 0.06 * 0.02 α 12 β 3 0.00 0.02
Predictor Predictor effect on SAM T2 as mediator (α paths) Mediator effect of SAM T2 on SAM T3 (β4 path) Mediated effect (αβ)
T1 b SE b SE b SE
Permissiveness α 13 0.07 0.05 β 4 0.41 * 0.13 α 13 β 4 0.03 0.02
Friends’ Approval α 14 0.07 0.04 β 4 0.41 * 0.13 α 14 β 4 0.03 0.02
Alcohol Use α 15 0.03 0.02 β 4 0.41 * 0.13 α 15 β 4 0.01 0.01
SAM α 16 0.28 * 0.11 β 4 0.41 * 0.13 α 16 β 4 0.12 * 0.05
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Note: Parent Permissiveness Toward Drinking; Friends’ Approval Toward Drinking; Student Alcohol Use; Simultaneous Alcohol and Marijuana (SAM) Use; b = unstandardized coefficient; SE = standard error

*

and bold denotes p < .05.

Discussion

We hypothesized that parental permissiveness and perceived friends’ approval of drinking, both of which contribute to heavier drinking (Mallett, Turrisi, Reavy, et al., 2019; Collins & Spelman, 2013; Krieger et al., 2016) and have been targeted in alcohol interventions (e.g., Grossbard et al., 2010; Turrisi et al., 2001, 2009), would also affect SAM use given that using alcohol is one component of SAM use. Findings from the current study illustrate that perceptions about parental permissiveness and friends’ approval toward drinking during the transition into college indirectly influenced SAM use by increasing drinking during the first year. These results offer preliminary evidence supporting the notion that parental permissiveness toward drinking and friends’ approval toward alcohol are risk factors for SAM use through their effects on drinking. One plausible explanation for this pattern of effects is that SAM use during this period occurs most often in situations associated with heavy drinking (e.g., lack of adult supervision, the presence of minors, high percentage of intoxicated individuals, private settings; Lipperman-Kreda et al., 2017, 2018). Thus, it is reasonable to assume that higher perceived parent and friend approval toward drinking increases exposure to and opportunity to engage in SAM use by increasing that likelihood that first-years will engage in heavy drinking.

Implications

Given the current findings, SAM use may be reduced by utilizing existing alcohol interventions that target parental permissiveness toward drinking (e.g., Ichiyama et al., 2009; LaBrie et al., 2016; Turrisi et al., 2001) or perceived peer drinking norms (see Cronce & Larimer, 2011; U.S. Department of Health & Human Services, 2016). Previous studies suggest that targeting both parents and students’ normative beliefs may be a more effective strategy for reducing alcohol use (e.g., Turrisi et al., 2009) and marijuana use (Grossbard et al., 2010). Taken together, targeting parental permissiveness toward drinking and peer drinking norms in adjunct preventative interventions early in the first year may be an effective strategy for reducing SAM use. Furthermore, identifying secondary effects of existing alcohol interventions on SAM use should be considered before researchers develop new SAM-specific interventions.

Limitations and Future Directions

First, the university from which students were sampled was predominantly White (77.9% of undergraduates in 2007; 75.4% in 2008). Although the prevalence of SAM use is found to be greater amongst Whites relative to Blacks and Hispanics (Patrick et al., 2019; Terry-McElrath et al., 2013), future studies are needed to determine how the current findings generalize to students of different races and ethnicities. Second, the current study only examined alcohol-specific predictors. Although findings from this study and others (e.g., Linden-Carmichael et al., 2019) have demonstrated that risk factors for drinking can also influence SAM use, SAM-specific predictors (e.g., friends’ approval of SAM use; White et al., 2019) should be considered in future studies.

A third limitation is that, at the time of data collection, all marijuana use was illegal in the study site’s state, which may not generalize to other states in which recreational and/or medicinal marijuana is legal. Generalizability may also be impacted by changes in marijuana use norms since data for the study were collected (i.e., 2007). Acceptability for marijuana use has increased in recent years; specifically, the percentage of 19- to 22-year-olds who perceived their close friends to disapprove of marijuana use (trying it once or twice, using occasionally, using regularly) has decreased by approximately 23–29% between 2007 (when data were first collected) and 2019 (Schulenberg et al., 2020). However, while norms surrounding marijuana use may have changed, the percentage of the current sample who reported any SAM use (25.5%) is consistent with recent national data in which approximately 20–23% of young adults reported engaging in SAM use (Looby et al., 2021; Patrick et al., 2019; Schulenberg et al., 2019).

Further, the percent of drinkers who reported SAM use in this study (34.6%) is consistent with other recent nationally representative samples (30%; Terry-McElrath & Patrick, 2018). Although SAM use has historically increased among drinkers (Schulenberg et al., 2019; Terry-McElrath & Patrick, 2018), closer examination reveals that this trend is consistent only among those 21 years or older and not among those represented in the present sample (i.e., incoming college students who are below the legal age to consume alcohol and marijuana). One explanation for this pattern is that obtaining alcohol and marijuana can be difficult for underaged adults to obtain. This suggests that incoming college students (typically 18–19 years of age) are an ideal population for interventions aimed to prevent this increase because they have not yet reached age 21 when SAM use increases and both alcohol and marijuana (in many jurisdictions) can be easily and legally obtained (Schulenberg et al., 2019; Terry-McElrath & Patrick, 2018).

Conclusion

In conclusion, findings from this study revealed that parental permissiveness toward drinking and greater perceptions of friends’ approval toward drinking assessed prior to entering college indirectly increased SAM use in the second year of college by increasing drinking during the first year. Identification of these novel pathways lends credibility to the notion that drinking-related interventions targeting parents and students separately may be effective at reducing SAM use. Thus, we recommend future studies examine the secondary effects of combined parent and peer interventions on SAM use.

Disclosure of Interest

The authors report no conflict of interest. This work was supported by the National Institutes of Health (NIH)/National Institute on Alcohol Abuse and Alcoholism (NIAAA) under grant numbers R01AA015737, R34AA026422, K01AA026854.

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