Longitudinal Associations between Homelessness and Substance Use: Investigating Demographic Differences for Young Adults in Treatment.

Objective: To examine prospective, bidirectional associations between homelessness and substance use frequency among young adults receiving substance use treatment in the United States. We also investigated potential differences across demographic subgroups. Methods: Young adults (N = 3717, Mage = 20.1, 28% female, 7.3% sexual/gender minority, and 37% non-Hispanic White) receiving substance use treatment in the U.S. completed assessments at intake, 3 months, 6 months, and 12 months post-intake. Latent growth curve models with structured residuals (LGC-SR) were used to examine cross-lagged associations between homeless days and frequency of substance use and associated problems. Models were stratified by sex, race/ethnicity, and sexual and/or gender minority status. Results: Overall, days spent homeless (µslope= -0.19, p = 0.046) and substance use frequency (µslope1= -6.19, p < 0.001) significantly decreased during treatment, with no significant cross-lagged associations between homeless days and substance use frequency. However, results differed by race and ethnicity. For non-Hispanic White young adults, greater substance use at treatment entry was associated with steeper declines in homeless days between-persons (ϕstandardized = -0.14, p = 0.04). For African Americans, homeless days at treatment entry were associated with greater increases in substance use between-persons (ϕstandardized = 0.29, p = 0.04). No significant differences were found by sex or sexual/gender minority status. Conclusions: Despite overall declines in homelessness and substance use during treatment, these outcomes may unfold differently for non-Hispanic White and African American young adults. More support may be needed for African American young adults reporting homelessness at treatment entry.

Associations between service use and behavioral health trajectories among young adults experiencing homelessness.

Purpose: To examine associations of service use (housing, mental health, substance use, education, and employment) with depression and substance use disorder (SUD) trajectories among young adults experiencing homelessness. Method: Secondary data come from 276 young adults who participated in an intervention to reduce substance use and sexual risk behaviors. Participants were recruited from three drop-in centers in Los Angeles County from 2018 to 2020, and completed surveys at baseline, 3-, 6-, 12-, and 24-months post-baseline. Latent growth curve models examined trajectories of depression and SUD; service use in the past three months was used to predict growth trajectories. Results: More frequent use of mental health services (but not other services) at baseline was associated with greater depression symptoms at baseline, linear declines in depression, and a quadratic increase in depression. Service use at baseline was not associated with likelihood of SUD at baseline or changes in SUD over time. Conclusions: Young adults in most need of behavioral services are likely to receive services for mental health, but not SUD. Use of mental health services may reduce depression symptoms over time, but continuing care may be needed to prevent symptom returns. More work is needed to connect young adults with SUD treatment and improve effectiveness of these services.

Perceived safety in community and service settings among young adults experiencing homelessness: Differences by sexual and gender identity.

Homelessness poses risks to the health and safety of young adults; particularly among sexual and gender minority (SGM) young adults. The current study sought to better understand service use and perceived safety in community and service settings among SGM and cisgender heterosexual (cis-hetero) young adults experiencing homelessness. Data come from a mixed-method, ecological momentary assessment study (n = 80; 43% sexual minority; 10% gender minority) in Los Angeles, California. Participants reported their current location (service vs. nonservice setting) and perceived safety. Multilevel modeling examined associations between identity, location, and perceived safety; qualitative interviews with 20 SGM participants added context to quantitative findings. Overall, service location was associated with greater perceived safety (ß = .27, p < .001). Compared to cis-hetero participants, cisgender sexual minorities (ß = -.23, p = .03) and sexual and gender minorities (ß = -.50, p = .002) reported lower perceived safety in service settings (vs. nonservice settings). Qualitative interviews revealed themes and subthemes detailing safe/unsafe spaces and interpersonal conflict in the community, and relationships with staff, peers, transphobia, and positive experiences in service settings.

Mobilizing a Community-Academic Partnership to Provide DIY Handwashing Stations to Skid Row Residents During COVID-19.

The coronavirus (COVID-19) pandemic is having a devastating impact on global health. In the United States and abroad, there is concern for how the novel coronavirus will affect vulnerable populations, including people experiencing homelessness. Individuals who lack stable housing are more likely to have preexisting health conditions and limited access to basic preventative hygiene practices such as handwashing and sanitizing. The situation has become critical in Los Angeles' Skid Row neighborhood, where nearly 5,000 unhoused residents (13% of the city's homeless population) reside on any given night. Community members' concerns have mounted as social and health services in the area have decreased, and early efforts to prevent the transmission of coronavirus did not adequately address the lack of access to handwashing stations and hand sanitizing products. This Practice Note details an academic-community partnership that uses grassroots organizing to provide "do-it-yourself" handwashing stations to the Skid Row neighborhood. We describe how an academic-community partnership was mobilized to establish innovative practices in response to the coronavirus, offering lessons and recommendations for others hoping to do similar work.

Development of a Measure to Assess Protective Behavioral Strategies for Pregaming among Young Adults.

Background: Although most young adults drink alcohol, there are specific drinking contexts that are associated with increased risk for alcohol-related consequences. One such drinking context is pregaming, which typically involves heavy drinking in brief periods of time and has consistently been linked to consequences within the pregaming event itself, on a night after pregaming, and in the long-term. Intervention efforts that specifically target this risky behavior are needed, but these efforts need to be informed by empirical work to better understand what behaviors young people engage in that can protect them from pregaming-related harms. Purpose: We designed this study to create a measure of protective behavioral strategies that young people use before, during, and after pregaming to inform future intervention work. Methods: We tested an item pool with 363 young adult college students who engaged in pregaming in the past year and conducted exploratory factor analysis to develop a 19-item Protective Behavioral Strategies for Pregaming (PBSP) scale, which featured four subscales of safety and familiarity, setting drink limits, pacing strategies, and minimizing intoxication. Results: Each subscale negatively and significantly correlated with measures of alcohol use and consequences, though subscales differed in their associations with specific pregaming outcomes and by sex. Conclusion: This initial exploratory examination of the PBSP scale's psychometric properties suggests that use of protective behavioral strategies used specifically during pregaming events may protect young people from heavy drinking and harms. More research with the PBSP scale is encouraged to determine its practical utility as a clinical and assessment tool with young people.

Identification and Description of Potentially Influential Social Network Members using the Strategic Player Approach.

Background: Diffusion of innovations theory posits that ideas and behaviors can be spread through social network ties. In intervention work, intervening upon certain network members may lead to intervention effects "diffusing" into the network to affect the behavior of network members who did not receive the intervention. The strategic players (SP) method, an extension of Borgatti's Key Players approach, is used to balance the (sometimes) opposing goals of spreading the intervention to as many members of the target group as possible, while preventing the spread of the intervention to others. Objectives: We sought to test whether members of the SP set have network position and non-network differences (such as demographic, attitudinal, or behavioral differences) compared to the remaining members of the target group (non-SPs). Methods: A first-year class at a private residential university (N = 1342) completed network and non-network measures. Analyses were restricted only to heavy drinkers, leading to a final analytic sample of 529. Results: SPs and non-SPs differed on multiple network variables, but did not differ on most demographic, attitudinal, and behavior variables. Conclusions: As designed, the SP program identified participants who were distinguished by their network position. The fact that they did not also differ on other characteristics shows the SPs are not significantly different than heavy drinkers who were not selected.

Causal Effects of Alcohol Intoxication on Sexual Risk Intentions and Condom Negotiation Skills Among High-Risk Men Who Have Sex with Men (MSM).

Alcohol use is a key risk factor for HIV infection among MSM, in part because intoxication may interfere with the use of prevention methods like condoms. However, few studies have examined whether this is due to alcohol's pharmacological or expectancy effects or explored the specific aspects of sexual decision-making that may be affected. In this study, high-risk, heavy drinking MSM (N = 121) were randomly assigned to receive either (1) alcohol beverages, (2) placebo beverages, or (3) control beverages, before navigating a video-based sexual risk scenario that assessed several aspects of sexual decision-making. Results showed that condom use intentions and negotiation behaviors were lower among alcohol and placebo participants compared with controls, but that few significant differences emerged between the alcohol and placebo groups. These findings contrast with similar past studies, and suggest that alcohol's expectancy effects may play a role in sexual decision-making.

Using Video Conferencing to Deliver a Brief Motivational Intervention for Alcohol and Sex Risk to Emergency Department Patients: A Proof-of-Concept Pilot Study.

Brief motivational intervention (MI) is an efficacious approach to reduce heavy drinking and associated sexual risk behavior among Emergency Department (ED) patients, but the intensity of demands placed on ED staff makes the implementation of in-person MIs logistically challenging. This proof-of-concept pilot study examined the acceptability and logistic feasibility of using video-conferencing technology to deliver an MI targeting heavy drinking and risky sexual behavior to patients in an ED setting. Rigorous screening procedures were employed to ensure that the pilot sample represents the target portion of ED patients who would benefit from this multi-target MI. Mixed qualitative and quantitative data from a sample of seven ED patients (57% Female; Mage = 35 years) who received MI by video conference consistently demonstrated high levels of satisfaction, engagement, and acceptability. The observed completion rate supports logistic feasibility, and patient feedback identified methods to improve the experience by using high-definition hardware, ensuring stronger network connectivity, and effectively communicating information regarding protection of privacy. Post-intervention patient ratings and independent ratings of the audio-recorded sessions (using the Motivational Interviewing Skills Coding system) were very high, suggesting that intervention fidelity and MI adherence was not compromised by delivery modality. Collectively, these data suggest video conferencing is a viable technology that can be employed to implement brief evidence-based MIs in ED settings.

Predictors of Housing Trajectories Among Young Adults Experiencing Homelessness in Los Angeles.

Experiencing homelessness during young adulthood is associated with negative health outcomes and understanding housing trajectories of young adults experiencing homelessness may aid in the development of evidence-based public health programs designed to serve this at-risk age group. In the present study, the authors examined baseline predictors of 24-month trajectories of housing stability and unsheltered housing among a sample of 271 young adults aged 18 to 25 recruited from drop-in centers in Los Angeles. In multivariate models, the authors found that identifying as multi-racial/other and better friendship quality at baseline were associated with less steep increases in the likelihood of stable housing over time. Being employed at baseline was associated with a less steep decrease in the probability of being unsheltered over time, while illicit drug use days associated with a steeper decrease in the probability of being unsheltered over time. Continued research is needed to establish important factors determining young adults' long-term housing trajectories in the effort to promote greater access and engagement with housing services.

Dynamic social network analysis of a brief alcohol intervention trial in heavy-drinking college students shows spillover effects.

BACKGROUND: Heavy-drinking college students tend to have close social networks, and there is theoretical and empirical support for the idea that behavior change can spread through those networks via close ties. The objective of this research was to determine whether intervention-induced behavior change in a subset of heavy drinkers in a sociometric (whole) college class-year social network is transmitted to other heavy drinkers in the network, resulting in reduced behavioral risk and change in network ties. METHODS: We conducted a controlled trial in which most of a first-year college class (N = 1236; 56.9% female) was enrolled, with alcohol use and social network ties measured early in each of three semesters. Following a baseline assessment, the network was divided into two groups, brief motivational intervention (BMI) and natural history control (NHC) according to dormitory residence location. A subset of heavy drinkers in each group was selected, and those in the BMI group received an in-person intervention. RESULTS: Using stochastic actor-oriented modeling, we found a significant tendency for participants in the BMI group to shed ties with individuals with similar drinking behaviors between the first and second semesters, relative to the NHC group. Furthermore, heavy drinkers with reciprocal ties to intervention recipients in the BMI group showed a significant reduction in drinks per week. CONCLUSIONS: Individual alcohol interventions appear to have effects both on behavior and network connections among individuals who did not receive the intervention. Continued research is needed to identify the optimal conditions for the diffusion of behavior change.

Exploring predictors of substance use disorder treatment engagement with machine learning: The impact of social determinants of health in the therapeutic landscape.

BACKGROUND: Improved knowledge of factors that influence treatment engagement could help treatment providers and systems better engage patients. The present study used machine learning to explore associations between individual- and neighborhood-level factors, and SUD treatment engagement. METHODS: This was a secondary analysis of the Global Appraisal of Individual Needs (GAIN) dataset and United States Census Bureau data utilizing random forest machine learning and generalized linear mixed modelling. Our sample (N = 15,873) included all people entering SUD treatment at GAIN sites from 2006 to 2012. Predictors included an array of demographic, psychosocial, treatment-specific, and clinical measures, as well as environment-level measures for the neighborhood in which patients received treatment. RESULTS: Greater odds of treatment engagement were predicted by adolescent age and psychiatric comorbidity, and at the neighborhood-level, by low unemployment and high population density. Lower odds of treatment engagement were predicted by Black/African American race, and at the neighborhood-level by high rate of public assistance and high income inequality. Regardless of the degree of treatment engagement, individuals receiving treatment in areas with high unemployment, alcohol sale outlet concentration, and poverty had greater substance use and related problems at baseline. Although these differences reduced with treatment and over time, disparities remained. CONCLUSIONS: Neighborhood-level factors appear to play an important role in SUD treatment engagement. Regardless of whether individuals engage with treatment, greater loading on social determinants of health such as unemployment, alcohol sale outlet density, and poverty in the therapeutic landscape are associated with worse SUD treatment outcomes.

A Longitudinal Exploration of How Connections to Staff Facilitate Efficacy and Service Use in Drop-in Centers Serving Youth Experiencing Homelessness.

INTRODUCTION: Youth experiencing homelessness (YEH) benefit from a variety of services to meet their immediate and long-term needs. Drop-in centers are a popular service venue used by YEH. However, the mechanisms responsible for engaging youth in drop-in services are not clear. The current study uses longitudinal data to explore the role of positive staff relationships in increasing youths' knowledge and efficacy to access and subsequently use drop-in center services. METHODS: 731 youth (Mage = 21.8, SD = 2.2, 25.1% female) accessing services at three drop-in centers in Los Angeles, California participated in the study. Surveys were completed at baseline, 1-month, and 3-months later. Path models examined the direct effect of positive relationships with adult staff on service use at the 3-month follow-up, and the indirect effect of service knowledge (assessed at the 1-month follow-up). RESULTS: The direct effect model showed that positive staff relationships at baseline were significantly associated with number of services used at the 3-month follow-up (aIRR = 1.24, 95% CI: 1.00, 1.54). Positive staff relationships were also associated with greater service knowledge at 1-month (b = 0.93, p < 0.001), which in turn was associated with greater service use at 3-months (IRR = 1.15, 95% CI: 1.04, 1.28). The indirect effect of service knowledge was significant (b = 0.13, p = 0.02), suggesting that the association between positive staff relationships and service use was completely mediated by service knowledge. CONCLUSIONS: The current study adds to the literature by demonstrating that positive relationships with staff lead to increased service use by increasing youths' knowledge and efficacy to access services. Efforts should be made to develop positive relationships with YEH in order to engage them in essential services needed to exit homelessness.

Sexual violence victimization among American college students studying abroad.

Objective: Research has just begun to identify American college students who study abroad as a group at-risk for sexual violence victimization. The purpose of the current study was to examine the context of these incidents. Participants: We utilized a large longitudinal sample of 2,428 United States college students studying abroad for between 4 and 21 weeks in 12 different foreign countries. Methods: We estimated descriptive statistics and logistic regression models to assess prevalence and correlates of sexual victimization abroad, as well as effect size comparisons to quantify changes in drinking abroad. Results: Over one-fifth of students experienced sexual violence while abroad, including sexual assault and verbal coercion. Women, younger students, those who experienced sexual violence prior, and heavier drinkers had the greatest odds of sexual violence victimization abroad. Conclusions: Findings point to the need for evidence-based programming to reduce sexual violence risk among American college students studying in foreign countries.

Understanding Changes in Social Cannabis Use among Young Adults During the COVID-19 Pandemic: A Social Network Analysis.

Introduction: As the COVID-19 pandemic has caused historic morbidity and mortality and disrupted young people's social relationships, little is known regarding change in young adults' social cannabis use following social distancing orders, or other factors associated with such changes before and during the pandemic. Methods: 108 young adult cannabis users in Los Angeles reported on their personal (egocentric) social network characteristics, cannabis use, and pandemic-related variables before (July 2019 - March 2020) and during the COVID-19 pandemic (August 2020 - August 2021). Multinomial logistic regression identified factors associated with increasing or maintaining the number of network members (alters) participants used cannabis with before and during the pandemic. Multilevel modeling identified ego- and alter-level factors associated with dyadic cannabis use between each ego and alter during the pandemic. Results: Most participants (61%) decreased the number of alters they used cannabis with, 14% maintained, and 25% increased. Larger networks were associated with a lower risk of increasing (vs. decreasing); more supportive cannabis-using alters was associated with a lower risk of maintaining (vs. decreasing); relationship duration was associated with a greater risk of maintaining and increasing (vs. decreasing). During the COVID-19 pandemic (August 2020 - August 2021), participants were more likely to use cannabis with alters they also used alcohol with and alters who were perceived to have more positive attitudes towards cannabis. Conclusions: The present study identifies significant factors associated with changes in young adults' social cannabis use following pandemic-related social distancing. These findings may inform social network interventions for young adults who use cannabis with their network members amid such social restrictions.

Examining indirect effects of advertising exposure on young adults' cannabis and nicotine vaping.

OBJECTIVE: To examine longitudinal associations between exposure to two types of advertisements (medical/recreational cannabis and e-cigarette retailers [vape shops]) and young adults' cannabis and nicotine vaping behavior. Positive and negative expectancies for cannabis and vaping nicotine were examined as mediators of these associations. METHOD: Secondary analysis of observational data from a longitudinal cohort of young adults recruited from Southern California (Wave 13: N = 2,411, 56% female, Mage = 23.6). Participants completed web-based surveys annually, reporting on advertising exposure in 2018, expectancies in 2019, and cannabis and nicotine vaping in 2020. Two path models were specified: (a) of past-month cannabis vaping only, nicotine vaping only, and co-use (vs. no vaping) and (b) of single product vaping (vs. co-use). Path analyses modeled direct and indirect associations between variables. RESULTS: Controlling for past-month cannabis and nicotine use and other covariates, there were no significant direct associations of advertising exposure with cannabis and/or nicotine vaping. However, the association between cannabis advertising exposure and vaping (cannabis only) was significantly mediated by positive cannabis expectancies (ß = 0.02, SE = 0.01, p = .03). Among those who vaped cannabis and/or nicotine in the past month at Wave 13, expectancies did not significantly mediate associations between advertising exposure and single product use (vs. co-use). CONCLUSIONS: Although exposure to cannabis advertisements may not be directly associated with young adults' cannabis vaping 2 years later, the effects of advertising exposure may be exerted indirectly by increasing positive beliefs about cannabis. Implications for public health policy are discussed. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Direct and indirect effects of mindfulness, PTSD, and depression on self-stigma of mental illness in OEF/OIF veterans.

OBJECTIVE: Two of the most common and costly mental health diagnoses among military veterans who served in the post-9/11 conflicts in Afghanistan and Iraq are posttraumatic stress disorder (PTSD) and depression, but over half of veterans who screen positive for these problems do not seek treatment. A key barrier is self-stigma of mental illness. Mindfulness has shown promise as an explanatory variable in the context of mental health symptoms and self-stigma, but these associations are underexplored in the veterans' literature. This study examines direct and indirect effects among mindfulness, PTSD and depression, and self-stigma in post-9/11-era military veterans. METHOD: A sample of 577 veterans from 3 large American cities completed surveys capturing mindfulness, symptoms of PTSD and depression, and self-stigma. A structural equation modeling approach was used to examine direct and indirect effects among study variables. RESULTS: Mindfulness was associated with less PTSD and depression and indirectly with less self-stigma through the PTSD pathway. PTSD was associated with more depression and self-stigma, and depression was not significantly associated with self-stigma. CONCLUSION: PTSD is strongly associated with self-stigma in military veterans, many of whom do not seek mental health treatment. Findings show that mindfulness is a promising intervention target for reducing symptoms of PTSD directly and reducing associated self-stigma of mental illness indirectly. Additional investigation of links between mindfulness, PTSD and depressive symptoms, and self-stigma in military veterans is warranted. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Multiple Minority Stress and Behavioral Health Among Young Black and Latino Sexual Minority Men.

Purpose: Young Black and Latino sexual minority men may experience multiple minority stressors, which may negatively impact behavioral health. To investigate this, longitudinal associations between multiple minority stressors and behavioral health outcomes were examined over a 2-year period. Methods: Data were from the Healthy Young Men's Cohort Study. The present study used five waves of data collected every 6 months from 2016 to 2019. Participants were young Black and/or Latino sexual minority men in Los Angeles, California (n = 448; aged 16-24). Participants self-reported their experiences of racial and homonegative discrimination, internalized homonegativity, alcohol use, and depressive symptoms. Latent growth curve models with time-varying covariates examined contemporaneous associations between minority stressors as well as general life stress and behavioral health measures. Results: After accounting for general life stress and demographic characteristics, racial discrimination was persistently associated with unhealthy alcohol use. Internalized homonegativity was associated with unhealthy alcohol use initially, but this association became non-significant over time. In models predicting depressive symptoms, racial discrimination was a significant predictor at early waves, and homonegative discrimination and internalized homonegativity emerged as significant predictors at later waves. Conclusion: These results help clarify which multiple minority stressors are more prominent in their relationship to young Black and Latino sexual minority men's unhealthy alcohol use and depressive symptoms. Interventions targeting multiple minority stressors may be needed at different times during young adulthood.

Egocentric Network Characteristics and Cannabis Use in a Sample of Young Adult Medical Cannabis Patients and Nonpatient Users.

OBJECTIVE: Social factors play an important role in young adults' substance use behaviors, but little is known about how egocentric social network factors are related to young adults' cannabis use. Young adults also report medicinal and recreational uses of cannabis, which may alter the strength of these relationships. Therefore, medical cannabis patient status and medicinal/recreational orientation toward cannabis were examined as moderators of these relationships. METHOD: Young adult medical cannabis patients (n = 182) and nonpatient users (n = 157) were surveyed in Los Angeles in 2015-2016 about their cannabis use, orientation (medicinal and/or recreational), and egocentric networks (cannabis use network size, social support network size, descriptive and injunctive norms). Regression models examined associations between network characteristics and past-90-day use and problematic use, and tested interactions between network characteristics and both patient status and cannabis use orientation. RESULTS: Only descriptive norms (adjusted incidence rate ratio [aIRR] = 1.19, 95% confidence interval [CI] [1.06, 1.33]) were associated with more frequent use, but not problematic use. Descriptive norms interacted with cannabis use orientation: descriptive norms were positively associated with cannabis use days among medicinally oriented users (aIRR = 1.22, 95% CI [1.02, 1.46]). However, this relationship was stronger for recreationally oriented users (aIRR = 1.62, 95% CI [1.31, 2.01]). No interactions were found predicting problematic use. CONCLUSIONS: Descriptive cannabis use norms among one's personal network members are an important variable predicting young adults' cannabis use, but not problematic use. Perceived descriptive norms may be a stronger motivator to use for recreational users than medicinal users.

Sex differences in poly-victimization among youth experiencing homelessness prior to substance use treatment.

BACKGROUND: Poly-victimization is common among youth experiencing homelessness (YEH) and youth in substance use treatment. To date, studies have not examined poly-victimization among these two intersecting populations. OBJECTIVE: To examine heterogeneity in lifetime victimization experiences among youth reporting homelessness at substance use treatment entry; identify demographic predictors of victimization class membership; and associations between victimization and clinical characteristics at treatment intake. PARTICIPANTS AND SETTING: 1270 adolescents and young adults reporting past 90-day homelessness in a nationwide substance use treatment data set. METHODS: Latent Class Analysis (LCA) and logistic regression were used to examine heterogeneity in poly-victimization experiences, and associations with demographics and clinical characteristics for males and females. RESULTS: Four victimization classes emerged for males, and five victimization classes emerged for females. The prevalence of victimization and trauma characteristics were higher for females, except physical victimization, which was higher for males. Age, race/ethnicity, and sexual minority status were related to poly-victimization class membership, but not consistently across classes. Compared to low or single victimization classes, youth in the poly-victimization class had higher odds of post-traumatic stress disorder, major depressive disorder, and exchange sex (among females); Poly-victimization class membership was not associated with duration of recent homelessness or substance use disorder diagnoses, when compared to low/less complex victimization. CONCLUSION: High rates of lifetime victimization were found for YEH in substance use treatment, with rates generally higher among females. Trauma-informed interventions are needed to address complex victimization experiences and poor mental health among unstably housed youth in treatment.

Peer selection and influence for marijuana use in a complete network of first-year college students.

BACKGROUND: Marijuana is the most frequently used illicit drug among college students, and there is a need to understand the social processes that contribute to young adults' marijuana use. Substance use behaviors tend to be more similar (homophilous) among individuals with social ties to one another. However, little is known about whether marijuana use homophily within young adult relationships is due to social selection (seeking out ties with similar marijuana use to one's own) or social influence (adopting similar marijuana use behaviors as one's ties), or both. METHODS: Students (N = 1,489; 54.6% female; Mage = 18.6 years) at one University completed online surveys in their first three semesters of college. Surveys assessed participant characteristics, marijuana use, and ties to up to 10 other students in the whole (sociocentric) network of first-year college students. Stochastic-actor oriented models (SAOMs) were used to analyze the co-evolution of marijuana use and social ties over time. RESULTS: Participants were more likely to select peers with similar past 30-day marijuana use as themselves. Concurrently, students' past 30-day marijuana use became more similar to their peers' use over time. DISCUSSION: Evidence for selection and influence effects were highly significant after controlling for network structure and other covariates indicating these processes may work in tandem to increase marijuana use homophily over the first year of college. This highlights the importance of relationships made early in the first-year of college, as these initial peer ties are likely to reinforce marijuana use behaviors that occur within these relationships.