Background <p>Cannabis use is common among adolescents and young adults, yet motives, especially self-medication, remain poorly understood in non-legalized contexts. This study explored differences among recreational, self-medicated, and dual (recreational + self-medicated) cannabis users in sociodemographic, substance use, and mental health characteristics within a large Spanish sample of adolescents and young adults.</p> Methods <p>Data were collected from 1,078 participants aged 16–30 who reported past-year cannabis use. Based on motives, users were categorized into three groups. Validated measures assessed cannabis use severity, concurrent substance involvement, nicotine dependence, alcohol-related consequences, and mental health. Bivariate analyses and multinomial logistic regressions were performed to identify predictors of group membership.</p> Results <p>Dual users comprised most participants (53.2%) and showed the most severe profile, including higher cannabis use frequency, greater scores on the Cannabis Abuse Screening Test (CAST) and the Brief-Marijuana Consequences Questionnaire (B-MACQ), more tobacco co-use, and poorer mental health. Self-medicated users (8.3%) showed greater nicotine dependence, higher risk for cannabis use disorder, and higher scores on the Reality Distortion subscale of the Oviedo Schizotypy Assessment Questionnaire-Abbreviated (ESQUIZO-Q–A) than recreational users (38.5%). Multinomial logistic regressions identified cannabis-related problems and use frequency as the strongest predictors of dual or self-medicated use.</p> Conclusions <p>Distinguishing cannabis use motives in adolescents and young adults is crucial, as dual users represent a highly vulnerable subgroup with substance-related and psychological risks. Prevention and intervention efforts should include motive-specific screening, address misconceptions about self-medication, and integrate mental health support, especially amid Spain’s evolving cannabis regulations.</p>