Background. Prescription opioids are the most frequently misused class of prescription drug among young adults aged 18–25, yet trajectories of opioid misuse and escalation are understudied. We sought to model opioid misuse patterns and relationships between opioid misuse, sociodemographic factors, and other substance uses. Methods. Participants were 575 young adults age 16–25 who had misused opioids in the last 90 days. Latent class analysis was performed with models based on years of misuse, recency of misuse, and alternate modes of administration within the past 12 months, 3 months, and 30 days. Results. Four latent classes emerged that were differentially associated with heroin, cocaine, and methamphetamine use, tranquilizer misuse, daily opioid misuse, and opioid withdrawal. Alternate modes of administering opioids were associated with increased risk for these outcomes. Sociodemographic factors, homelessness, prescription history, and history of parental drug use were significantly associated with riskier opioid misuse trajectories. Conclusion. Young adults who reported more debilitating experiences as children and adolescents misused opioids longer and engaged in higher risk alternate modes of administering opioids. Data on decisions both to use and to alter a drug’s form can be combined to describe patterns of misuse over time and predict important risk behaviors. 1. Introduction Over the past decade, prescription drug misuse has increased significantly in the U.S. [1, 2] and is most prevalent among young adults 18 to 25 years of age [2, 3]. Prescription opioids, such as hydrocodone and oxycodone, are the most frequently misused class of prescription drug among young adults . Prescription opioids are a particularly important public health concern since opioid misuse is associated with a range of negative health outcomes, including injection drug use , drug dependence [2, 5], and fatal overdose [6, 7]. Prescription opioid trajectories among young adults begin with initiation into misuse  and include various patterns of misuse over a period of years [9, 10]. Features of opioid use trajectories, including duration of misuse and mode of administration, have been linked to negative outcomes among young adults. Individuals who initiate opioid misuse earlier in their lives or have misused opioids for several years have a greater likelihood of developing a substance abuse disorder [11, 12]. Misusing opioids for a period of years has been linked to transitioning to heroin among young injection drug users (IDUs) . Among adults, a longer duration
L. D. Johnston, P. M. O'Malley, J. G. Bachman, and J. E. Schulenberg, Monitoring the Future National Results on Adolescent Drug Use: Overview of Key Findings, Institute for Social Research, The University of Michigan, Ann Arbor, Mich, USA, 2013.
Substance Abuse and Mental Health Services Administration (SAMHSA), Results from the 2012 National Survey on Drug Use and Health: Volume I. Summary of National Findings, Office of Applied Studies, Rockville, Md, USA, 2013.
S. E. Lankenau, M. Teti, K. Silva, J. J. Bloom, A. Harocopos, and M. Treese, “Patterns of prescription drug misuse among young injection drug users,” Journal of Urban Health, vol. 89, no. 6, pp. 1004–1016, 2012.
R. D. Weiss, J. S. Potter, S. E. Provost et al., “A multi-site, two-phase, Prescription Opioid Addiction Treatment Study (POATS): rationale, design, and methodology,” Contemporary Clinical Trials, vol. 31, no. 2, pp. 189–199, 2010.
L. J. Pauozzi and Y. Xi, “Recent changes in drug poisoning mortality in the United States by urban-rural status and by drug type,” Pharmacoepidemiology and Drug Safety, vol. 17, no. 10, pp. 997–1005, 2008.
S. E. Lankenau, M. Teti, K. Silva, J. J. Bloom, A. Harocopos, and M. Treese, “Initiation into prescription opioid misuse amongst young injection drug users,” International Journal of Drug Policy, vol. 23, no. 1, pp. 37–44, 2012.
R. Daniulaityte, R. Falck, and R. G. Carlson, “Illicit use of buprenorphine in a community sample of young adult non-medical users of pharmaceutical opioids,” Drug and Alcohol Dependence, vol. 122, no. 3, pp. 201–207, 2012.
S. E. Lankenau, S. M. Schrager, K. Silva et al., “Misuse of prescription and illicit drugs among high-risk young adults in Los Angeles and New York,” Journal of Public Health Research, vol. 1, no. 1, pp. 22–30, 2012.
C. J. Boyd, C. J. Teter, B. T. West, M. Morales, and S. E. McCabe, “Non-medical use of prescription analgesics: a three-year national longitudinal study,” Journal of Addictive Diseases, vol. 28, no. 3, pp. 232–242, 2009.
S. E. McCabe, B. T. West, M. Morales, J. A. Cranford, and C. J. Boyd, “Does early onset of non-medical use of prescription drugs predict subsequent prescription drug abuse and dependence? Results from a national study,” Addiction, vol. 102, no. 12, pp. 1920–1930, 2007.
S. F. Butler, R. A. Black, J. M. G. Serrano, M. E. Wood, and S. H. Budman, “Characteristics of prescription opioid abusers in treatment: prescription opioid use history, age, use patterns, and functional severity,” Journal of Opioid Management, vol. 6, no. 4, pp. 239–252, 2010.
é. Roy, N. Arruda, and P. Bourgois, “The growing popularity of prescription opioid injection in downtown Montréal: new nhallenges for harm reduction,” Substance Use & Misuse, vol. 46, no. 9, pp. 1142–1150, 2011.
A. M. Young, J. R. Havens, and C. G. Leukefeld, “Route of administration for illicit prescription opioids: a comparison of rural and urban drug users,” Harm Reduction Journal, vol. 7, article 24, 2010.
T. C. Green, R. Black, J. M. Serrano, S. H. Budman, and S. F. Butler, “Typologies of prescription opioid use in a large sample of adults assessed for substance abuse treatment,” PLoS ONE, vol. 6, no. 11, Article ID e27244, 2011.
S. E. McCabe, J. A. Cranford, C. J. Boyd, and C. J. Teter, “Motives, diversion and routes of administration associated with nonmedical use of prescription opioids,” Addictive Behaviors, vol. 32, no. 3, pp. 562–575, 2007.
N. R. Whitesell, J. Beals, C. M. Mitchell et al., “Latent class analysis of substance use: comparison of two American Indian reservation populations and a national sample,” Journal of Studies on Alcohol, vol. 67, no. 1, pp. 32–43, 2006.
K. L. Nylund, T. Asparouhov, and B. O. Muthén, “Deciding on the number of classes in latent class analysis and growth mixture modeling: a Monte Carlo simulation study,” Structural Equation Modeling, vol. 14, no. 4, pp. 535–569, 2007.
S. L. Clark and B. O. Muthén, Relating latent class analysis results to variables not included in the analysis [monograph on the internet], Muthén & Muthén, Los Angeles, Calif, USA, 2009, http://www.statmodel.com/download/relatinglca.pdf.
A. Kecojevic, C. F. Wong, S. M. Schrager et al., “Initiation into prescription drug misuse: differences between lesbian, gay, bisexual, transgender (LGBT) and heterosexual high-risk young adults in Los Angeles and New York,” Addictive Behaviors, vol. 37, no. 11, pp. 1289–1293, 2012.
H. L. Corliss, M. Rosario, D. Wypij, S. A. Wylie, A. L. Frazier, and S. B. Austin, “Sexual orientation and drug use in a longitudinal cohort study of U.S. adolescents,” Addictive Behaviors, vol. 35, no. 5, pp. 517–521, 2010.
B. Fischer, J. Rehm, J. Patra et al., “Crack across Canada: comparing crack users and crack non-users in a Canadian multi-city cohort of illicit opioid users,” Addiction, vol. 101, no. 12, pp. 1760–1770, 2006.
é. Roy, M. Robert, é. Vaillancourt, J.-F. Boivin, J. Vandermeerschen, and I. Martin, “Residential trajectory and HIV high-risk behaviors among Montréal street youth—a reciprocal relationship,” Journal of Urban Health, vol. 88, no. 4, pp. 767–778, 2011.
R. G. Thompson and D. S. Hasin, “Cigarette, marijuana, and alcohol use and prior drug treatment among newly homeless young adults in New York City: relationship to a history of foster care,” Drug and Alcohol Dependence, vol. 117, no. 1, pp. 66–69, 2011.
K. Silva, S. M. Schrager, A. Kecojevic, and S. E. Lankenau, “Factors associated with history of non-fatal overdose among young nonmedical users of prescription drugs,” Drug and Alcohol Dependence, vol. 128, no. 1-2, pp. 104–110, 2013.
S. E. McCabe, B. T. West, C. J. Teter, and C. J. Boyd, “Medical and nonmedical use of prescription opioids among high school seniors in the United States,” Archives of Pediatrics and Adolescent Medicine, vol. 166, no. 9, pp. 797–802, 2012.
M. Fibbi, K. Silva, K. Johnson, D. Langer, and S. E. Lankenau, “Denial of prescription opioids among young adults with histories of opioid misuse,” Pain Medicine (United States), vol. 13, no. 8, pp. 1040–1048, 2012.
S. P. Stanos, P. Bruckenthal, and R. L. Barkin, “Strategies to reduce the tampering and subsequent abuse of long-acting opioids: potential risks and benefits of formulations with physical or pharmacologic deterrents to tampering,” Mayo Clinic Proceedings, vol. 87, no. 7, pp. 683–694, 2012.