Full length articleMarijuana use trajectories during college predict health outcomes nine years post-matriculation
Introduction
Marijuana use is highly prevalent, with approximately one in ten U.S. adults and one-third of college students having used during the past year (Johnston et al., 2014; Substance Abuse and Mental Health Services Administration (SAMHSA), 2014). Recent legislative trends toward decriminalization and legalization have been accompanied by declining perceptions of marijuana’s harmfulness (Johnston et al., 2014, SAMHSA, 2014). Given that emerging adulthood is a critical developmental stage with respect to identity exploration and establishing long-term adult roles, the consequences of marijuana use during this period could be substantial and enduring (Arnett, 2005). Young adulthood is also the peak developmental period for marijuana use and related problems (SAMHSA, 2014).
Public perceptions notwithstanding, abundant research evidence from both cross-sectional and longitudinal studies supports the association between marijuana use and a variety of psychosocial and health outcomes, especially when use begins early or is frequent, although not all studies have controlled for potential confounds such as alcohol and tobacco use (for reviews, see Hall, 2015, Joshi et al., 2014, Thomas et al., 2014). For example, marijuana use has been linked to psychosis (Di Forti et al., 2015, Di Forti et al., 2009, Fergusson et al., 2005, Hall, 2015, Henquet et al., 2005, Moore et al., 2007, van Os et al., 2002), bipolar disorder (Lagerberg et al., 2014), and major depression (Juon et al., 2011, Lynne-Landsman et al., 2010). The apparent dose-response relationship is particularly concerning given the increasing potency of marijuana during the past several decades (Mehmedic et al., 2010). Marijuana’s physical health effects include respiratory outcomes such as chronic bronchitis, airway inflammation, and decreased pulmonary function (Joshi et al., 2014, Tashkin, 2013), as well as increased risk for cardiovascular disease and acute cardiac events (Jouanjus et al., 2014, Mittleman et al., 2001, Mukamal et al., 2008, Thomas et al., 2014). Accordingly, some evidence indicates that health care utilization is higher for frequent marijuana users than non-users, namely for respiratory illness and injuries, even when excluding tobacco smokers (Polen et al., 1993).
Studies using group-based trajectory modeling can provide a more complete picture of the association between marijuana use patterns during adolescence and health outcomes in young adulthood. Despite methodological differences (e.g., frequency measures, age ranges, number of trajectory groups), certain commonalities emerge from the existing research utilizing this method. Most include a group that abstains from marijuana use, a group that consistently uses infrequently, and a group that consistently uses at high frequencies (Brook et al., 2013, Caldeira et al., 2012, Homel et al., 2014, Schulenberg et al., 2005). Many studies also identified groups with increasing or decreasing frequency of use over time (Brook et al., 2013, Caldeira et al., 2012, Ellickson et al., 2004, Schulenberg et al., 2005) or with different ages of onset (Flory et al., 2004).
In these studies, the trajectory groups that abstain from marijuana use throughout adolescence and young adulthood generally fare best in terms of education, employment, health, and social outcomes (Brook et al., 2013, Caldeira et al., 2012, Ellickson et al., 2004, Flory et al., 2004, Homel et al., 2014, Schulenberg et al., 2005). In contrast, the chronic trajectory groups generally exhibit poor outcomes related to employment and finances (Brook et al., 2013), education (Homel et al., 2014), alcohol and tobacco use (Schulenberg et al., 2005), and mental health (Brook et al., 2011, Caldeira et al., 2012). Even among an “early high” trajectory group (i.e., frequent use at age 13 that declined and stabilized by age 18), self-ratings of overall health at age 29 were significantly lower relative to the other trajectory groups (Ellickson et al., 2004). Nevertheless, few studies have examined young adult outcomes related to physical and mental health, and more comprehensive measures of these outcomes are needed. Additionally, previous studies have been limited in their ability to account for alcohol and tobacco use, which covary with marijuana use (Jackson et al., 2008).
The present study builds on our team’s prior work examining health outcomes in young adulthood in relation to marijuana use trajectories during college (Caldeira et al., 2012). Among a sample of 1253 college students studied over seven years, we identified six distinct trajectories of marijuana use frequency spanning the first six years of the study (see Fig. 1), which – as noted above – were significantly associated with several health outcomes in the seventh year, even after adjusting for baseline health status, demographics, alcohol use, and tobacco use. The present study aims to extend this prior research to evaluate what, if any, relationship might exist between marijuana use trajectory group membership during college and self-reported health outcomes measured in Year 10 (i.e., nine years post-matriculation). An important goal of this work was to replicate our earlier models to understand whether the observed associations with certain health outcomes would persist as participants approached age 30. We hypothesized that marijuana trajectory group membership would be significantly associated with health outcomes in Year 10, even after accounting for alcohol and tobacco use, demographics, and baseline health status.
Section snippets
Study design
Data were collected as part of the College Life Study, which followed a cohort of 1253 individuals originally recruited in 2004 as incoming freshmen at one large public university (Arria et al., 2008, Vincent et al., 2012). After screening the entire incoming class of students ages 17–19 (82% response rate), a sample was selected for longitudinal follow-up, with oversampling of individuals who used an illicit drug at least once during high school. Baseline and annual follow-up assessments
Health outcomes at Year 10
Among the overall sample at Year 10, approximately one-third (34%) rated their health as “excellent” and 58% rated their health as “good.” Approximately half visited a health provider for physical health problems at least once during the past year (52%) or had at least one day when their usual activities were limited by illness (46%). Fewer visited a provider for mental health problems (16%) or had their usual activities limited by an emotional problem (13%). Limiting usual activities due to an
Discussion
In this study of young adults assessed annually for ten years since college entry, the trajectory of students’ marijuana use patterns during and immediately following college was significantly associated with seven health outcomes measured in their late 20s, even after accounting for background risk factors and concomitant rates of change in alcohol and tobacco use. Whereas an earlier report on this sample documented marijuana-related differences in health outcomes in Year 7 (Caldeira et al.,
Funding
Funding for this study was provided by the National Institute on Drug Abuse (R01DA14845, Dr. Arria, PI). The National Institute on Drug Abuse had no further role in the study design; in the collection, management, analysis, and interpretation of the data; in the writing of the manuscript; or in the decision to submit the paper for publication.
Contributors
A.M. Arria and K.E. O’Grady contributed to the overall scientific direction of the project. K.M. Caldeira and A.M. Arria developed the manuscript. K.M. Caldeira, B.A. Bugbee, and K.B. Vincent managed the literature searches and summaries of previous work. K.M. Caldeira and K.E. O’Grady performed the statistical analyses. K.B. Vincent and B.A. Bugbee managed the day-to-day operational aspects of data collection and supervised staff involved in data collection. All authors assisted with writing
Conflicts of interest
None.
Acknowledgement
Special thanks are extended to Hannah Allen, the interviewing team, and the participants.
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