This study analyzes the process of drafting State Law No. 17,618/2023, which establishes access to medical cannabis through the Unified Health System (SUS) of the state of São Paulo, in light of John Kingdon’s (1995) Multiple Streams Framework, seeking to understand how medical cannabis transitioned from a marginalized position to becoming the subject of state public policy. This is a qualitative, analytical, and retrospective study, structured as a case study of the legislative process between 2019 and January 2023, with data collected through documentary and legislative analysis, a literature review, institutional documents from ALESP and the judiciary, and news coverage from that period. The results highlight the convergence of Kingdon’s three streams: in the problem stream, the massive judicialization of access to cannabidiol—a 544% increase in lawsuits between 2019 and 2022 and state spending of R$ 73.7 million—transformed a medical condition into an urgent public problem; in the solutions stream, scientific evidence, ANVISA’s RDC No. 327/2019, and the actions of the Parliamentary Front for Medical Cannabis consolidated the technical feasibility of the proposal; in the political stream, the transition of government in 2023 created a window of opportunity. It can be concluded that policy entrepreneurs—legislators, patients, family members, and associations—connected the three streams at the right moment, highlighting the central role of social mobilization in policy formulation within complex contexts, although partial vetoes and budgetary constraints indicate that legislative approval is only the first step toward ensuring access.