Prescription drug misuse represents a worldwide public health concern, particularly in high-income countries.1, 2, 3, 4, 5 Some of the consequences of prescription drug misuse, such as emergency room visits and overdoses, are most prevalent during adulthood and have increased substantially over the past two decades.3, 4 Approximately one in seven (14%) individuals aged 18–25 years in the USA reports prescription drug misuse in the past year (7% prescription opioids, 7% prescription stimulants, and 6% prescription tranquilisers).5, 6, 7 A legitimate concern exists that the high prevalence of prescription drug misuse places many adolescents and young adults at great risk of developing substance use disorder symptoms and other adverse outcomes in later life.8, 9, 10 Based on the high addiction potential associated with prescription drug misuse, adolescents and young adults might not mature out of prescription drug misuse in the same way that they mature out of other experimental substance use.11 Below, we briefly highlight the most commonly misused classes of prescription medication: opioids, stimulants, and sedatives or tranquilisers.
Prescription opioid misuse is a significant cause for concern. Several studies have shown that young people initiate prescription opioid misuse as early as elementary and middle school, where they typically obtain prescription opioids from a friend or from their own leftover prescriptions to relieve physical pain.12, 13, 14 Adolescents who misuse prescription opioids are most likely to co-ingest these prescription drugs with marijuana and alcohol, followed by cocaine and benzodiazepines.15 Several characteristics associated with prescription opioid misuse (eg, frequency, co-ingestion, and multiple opioids) have been shown to increase the risk of substance use disorder symptoms.16 Although most young people cease prescription opioid misuse over time, evidence suggests that about a third continue to misuse prescription opioids, placing themselves at high risk for adverse consequences such as overdose and substance use disorders.12, 16
Research in context
Evidence before this study
Prescription drug misuse is most prevalent during young adulthood (ages 18–25 years). Although existing evidence suggests prescription drug misuse is associated with an increased risk of developing substance use disorder symptoms, which long-term patterns of prescription drug misuse are associated with substance use disorder symptoms that persist during adulthood is not known. We searched PubMed for studies published in English before April 1, 2019, investigating long-term trajectories of prescription drug misuse during the transition from adolescence to adulthood. We did one major search of the scientific literature for prescription drug misuse trajectories in PubMed using the query (“prescription drug misuse” OR “nonmedical use” OR “medical misuse” OR “medication misuse” OR “opioid” OR “stimulant” OR “benzodiazepine” OR “sedative” OR “tranquilizer”) AND (“longitudinal” OR “trajectories” OR “prescription” OR “adolescence” OR “young adult”). We checked citations of relevant publications and searched the reference lists of selected articles in PubMed and Google Scholar. Existing research suggests that many studies do not adequately account for the frequency of prescription drug misuse or polysubstance use over time. Longitudinal studies identifying long-term trajectories of prescription drug misuse and identifying predictors of high-risk trajectories are scarce and needed.
Added value of this study
This national longitudinal multicohort study is, to the best of our knowledge, the first to identify trajectories of prescription drug misuse for three drug classes (opioids, stimulants, and sedatives or tranquilisers) during the transition from adolescence to adulthood. Using a follow-up period of 17 years, we found evidence of five unique prescription drug misuse trajectories, and the age at which high frequency of misuse peaked both differentiated and defined the trajectories. Later peak trajectories were associated with greater odds of having substance use disorder symptoms at age 35 years than were rare prescription drug misuse peak trajectories. Among adolescents who engaged in prescription drug misuse, we found that the strongest predictors of developing high-risk trajectories included high-school binge drinking, cigarette smoking, marijuana use, poly-prescription drug misuse, white race, and not completing a 4-year university degree by age 35 years.
Implications of all the available evidence
Any high-frequency prescription drug misuse serves as a strong signal for substance use disorder symptoms during adulthood, especially later peak trajectories. Our findings could help practitioners identify which individuals are at greatest risk of developing prescription drug misuse and substance use disorders during the transition from adolescence to adulthood and thus enhance targeting of prevention and intervention strategies.
Prescription stimulant misuse is most likely to be initiated during late adolescence, with some young people starting as early as elementary and middle school.13, 14 Adolescents typically obtain these medications for free or buy them from a friend.13, 14 Among young adults, full-time university students and university graduates have the highest rates of prescription stimulant misuse.10, 17 Approximately one in ten US college students has engaged in prescription stimulant misuse in the past year; most of these individuals have co-ingested with other substances, most often alcohol.10, 17 Although academic enhancement is the most prevalent motivation for prescription stimulant misuse among young people without attention deficit hyperactivity disorder, no evidence is available to support the efficacy of prescription stimulants to improve academic performance in real-world settings among young people without attention deficit hyperactivity disorder.18
Less longitudinal research has been done on the misuse of prescription sedatives or tranquilisers among adolescents and young adults compared with other prescription drug classes.19 Young people are most likely to initiate prescription sedative or tranquiliser misuse during high school and most often obtain these medications for free from their friends to relax.13, 14 Based on cross-sectional studies, prescription sedative or tranquiliser misuse is most prevalent during young adulthood,7, 14 especially among young adults not attending university.10, 17 Prescription sedative or tranquiliser misuse during adolescence often involves co-ingestion with alcohol and marijuana and has been shown to result in high-risk behaviours such as impaired driving.20, 21
Polysubstance use involving prescription drugs and other substances is most prevalent among adolescents and young adults.7, 12, 21 A regional study assessed substance use in young people from grade 10 (ages 15–16 years) through to age 21 years and found that all individuals who reported heavy non-medical prescription opioid misuse (ie, ten times or more per year) had also used marijuana and other drugs.12 These findings reinforce the importance of taking into account frequency of use and polysubstance use when studying prescription drug misuse trajectories. Additionally, approximately 73% of adolescents who misuse prescription sedatives or tranquilisers have co-ingested with other substances including alcohol, marijuana, prescription opioids, and prescription stimulants.21 Co-ingestion of prescription drugs with other substances can have synergistic effects and increase the risk of acute and long-term substance-related consequences.16 The high rates of polysubstance use associated with prescription drug misuse support examination of trajectories that combine prescription drug classes and assessment of a wide range of substance-related consequences to account for the overlap in prescription drug misuse and that of other substances.
Short-term longitudinal studies have examined the course of prescription drug misuse during distinct developmental periods (eg, adolescence or young adulthood) or for individual prescription drug classes.12, 22 Long-term longitudinal research is needed to understand prescription drug misuse trajectories from adolescence to adulthood across multiple prescription drug classes (ie, opioids, stimulants, and sedatives or tranquilisers), to consider long-term associations with substance use disorder symptoms, and to determine the characteristics of prescription drug misuse trajectories that are most problematic. The main objectives of the present study were to assess long-term prescription drug misuse trajectories for three prescription medication classes (opioids, stimulants, and sedatives or tranquilisers) from late adolescence (age 18 years) through to adulthood (age 35 years), to examine the extent to which different long-term prescription drug misuse trajectories are associated with substance use disorder symptoms at age 35 years, and to identify risk factors associated with high-risk prescription drug misuse trajectories.