The medical marijuana (MMJ) system has been established for the first time in Thai history since February 19, 2019, according to the Narcotic Control Act 2019 (7th edition) . This study aimed to find essential research questions regarding the implementation and impacts of and design the monitoring and evaluation system for the MMJ policy in Thailand. Research methods employed include a literature review, 22 in- depth interviews with key stakeholders, two focus group interviews covering nine service providers and patients, and a participatory observation in the MMJ clinic at the Ministry of Public Health. Our crucial findings cover: (a) the Thai MMJ system is complex, consisting of the sub-systems: modern medicine, Thai traditional medicine, and local community medicine. These three sub- systems are not harmonized. Patients could not access and benefit from the whole system, resulting in many of these patients having to use illegal marijuana products. ( b) MMJ is a new matter in Thailand and could provide both benefits and drawbacks for the Thai society; hence it is essential and urgent for Thailand to have an MMJ related knowledge generation system and an MMJ policy impact monitoring and evaluation system. (c) MMJ movement in Thailand has attributes like “political economy,” which means the MMJ policies may be driven by benefits rather than medical rationale. The proposed policy recommendations include follows. (1) Establish an advisory committee containing various capability dimensions and socially accepted, and have no conflict of interest. (2) Strengthen the MMJ service system in a way incorporating the advantages of all three MMJ sub-systems. (3) Urgently invest in the policy impact monitoring and evaluation system, including evaluating the supply, service utilization, and short-term and long-term consequences. (4) Promote Thai people’s health literacy regarding MMJ is crucial to prevent them from being victims of false information of the illegal MMJ providers. (5) Study the efficacy and the cost-effectiveness of various MMJ products in Thailand using the Thai culture-relevant, modified scientific method. And (6) study future MMJ policies for Thailand to inform policy decision making guided by scientific evidence.