Substance addiction in young adults is particularly problematic. Yet, much remain at stake in understanding the specifics of this population’s access to services. The objective of this study is to explore young adults’ initiation of substance misuse treatment. Our study sample was composed of 35 individuals aged 18 to 30 with problematic psychoactive substance use who have been identified in criminal courts, hospital emergency departments, and Health and Social Services Centers in Québec (Canada). A thematic analysis was performed on the 62 semi-structured interviews conducted with participants. Three components emerged. First, personal elements—expectations, individual motivations, perceptions of use, and capacity to control it—influence initiation of substance misuse treatment. Second, family and peers have noticeable influences. Finally, system characteristics and prior care experiences also shape the process. Consideration should be given to tailor interventions that can reach young adults and encourage them to initiate appropriate care.