ObjectiveTo investigate prevalence and correlates of medical use and misuse of psychoactive prescription medications among US youth and young adults.DesignCross-sectional, self-reported surveys from the 2015–2018 National Survey of Drug Use and Health. Sampling was probabilistic and nationally representative.SettingThe target population included individuals from households, non-institutional group quarters (eg, college dormitories) and civilians living on military bases. Questionnaires were completed using computer-assisted self-interview methods.ParticipantsOur analytical sample included youth and young adults aged 12–25 years (n=110 556). Psychoactive prescription medication misuse was a report by the respondent that they had used psychoactive prescription medications in the past year in any way not directed or prescribed for them. Medical use was defined as past-year use without a report of misuse. Because certain variables were assessed only among adults, our multivariable analysis to identify correlates of misuse was restricted to young adults aged 18–25 years (n=55 690).ResultsAmong US youth aged 12–17 years, 25.0% reported use of any psychoactive prescription medication assessed, and 5.7% reported past-year use of at least two psychoactive prescription medications. Among youth who used any psychoactive prescription medications, 20.9% (1.3 million) reported misuse; 3.4% were classified as having substance use disorder. Past-year use of each psychoactive prescription medication was: opioids (19.0%), stimulants (7.2%), tranquillisers (4.3%) and sedatives (2.2%). Among users of each psychoactive prescription medication, the estimated percentage reporting misuse was as follows: opioids (17.6%, 0.8 million), stimulants (24.2%, 0.4 million), tranquillisers (40.1%, 0.4 million) and sedatives (14.2%, 80 000). Among users of each psychoactive prescription medication, the estimated percentage having substance use disorder was as follows: opioids 2.6%, stimulants 3.0%, tranquillisers 7.0% and sedatives 3.6%. Analyses among young adults aged 18–25 years revealed that, compared with never users of non-prescription substances (including alcohol, tobacco, marijuana, cocaine, heroin), opioid misuse increased with: more recent use of non-prescription substances (adjusted prevalence ratios (APRs)=8.26, 2.75 and 2.41 for past ≤30-day, ≤12-month and >12-month use, respectively); and a higher number of substances used (APRs=1.69, 3.44, 6.82, 10.60 and 20.60 for 1, 2, 3, 4 and 5+ substances, respectively) (all p<0.05). Similar patterns were seen for stimulants, tranquillisers and sedatives.ConclusionsIt is important to monitor the diversity of medication misuse behaviours among youth and young adults, given their potential for abuse liability. Modifiable risk factors for prescription substance misuse, such as tobacco and other non-prescription substance use, underscore the need for comprehensive approaches towards health promotion among youth and young adults.