Background – Persons with substance use problems make up a considerable proportion of mental health care service users worldwide. Since 2009, Belgian mental health care underwent a nation-wide reform (‘Title 107’) aiming at realizing a mental health care system that fosters more adequate collaboration, promotes de-categorization between and across different services, and is more responsive to the support needs of all service users. Despite the fact that persons with substance use problems were named as a prioritized target group, the way this reform impacted the lives and recovery journeys of persons with substance use problems remains understudied. The presented qualitative study focuses on the lived experiences of persons with substance use problems and aims to unravel the underlying dynamics impacting the accessibility of mental health care services. Methods – Data were collected by means of in-depth interviews with a heterogeneous sample (n=52) of persons with substance use problems, including persons who do not have access to services, recruited from five regional mental health networks. Interviews were analyzed thematically. Results – Five dynamic themes influencing the accessibility of mental health care for persons with substance use problems come to the fore: fragmentation of care and support, the importance of “really listening”, balancing between treatment-driven and person-centered support, the ambivalent role of peers, and the impact of stigma. Discussion – Despite the ‘Title 107’ reform, participants still experienced mental health care services as ‘islands in the stream’, pointing to four priorities for future policy and practice development: breaking the vicious cycles of waiting times, organizing relational case management, tackling stigma and centralizing lived experiences, and fostering recovery-promoting collaborations.