Introduction: Non-communicable diseases (NCDs) constitute significant contributors to global morbidity and mortality, with Thailand being no exception. Adhering to prescribed medications plays a pivotal role in the treatment and management of these diseases. Nevertheless, more than half of the patients encounter difficulties in adhering to the recommended treatment regimen. This not only affects patients in terms of complications, disability, premature mortality, but also leads to escalated healthcare costs attributed to the care of patients with complications and disabilities. In the Thai healthcare context, there appears to be a dearth of understanding regarding the definition and significance of medication adherence among healthcare providers, alongside policy-level factors linked to this crucial aspect of treatment. Previous studies have primarily concentrated on patient-level determinants. Specific objectives: 1) To synthesize knowledge regarding the definitions, meanings, and policy factors that influence medication adherence of patients with NCDs, based on relevant documents and research studies both domestically and internationally. 2) To analyze the definitions and meanings of medication adherence among patients with NCDs attending community hospitals under the Ministry of Public Health of Thailand. Additionally, to investigate the policy factors affecting medication adherence through expert consensus. Method: This study synthesizes knowledge related to the definitions, meanings, and policy factors influencing medication adherence in patients with NCDs, employing Cooper’s literature synthesis method (2007). This acquired knowledge is subsequently utilized to formulate the initial set of questionnaires, encompassing the definitions and meanings of medication adherence, as well as policy factors. The questionnaires are further assessed for expert consensus using the Delphi technique, gathering opinions from 21 experts, divided into three distinct groups. The first group, consisting of five experts, is responsible for decision-making, involvement, and oversight of medication policies. The second group, comprising twelve experts, focuses on implementing policy responses related to medication and its usage. Finally, there is a group of four academic experts. Data is collected in two rounds to solicit opinions from these expert groups. In the second round, the same questionnaire is employed, enriched with median values, interquartile ranges, and reference points, allowing experts to provide self-assessments and evaluate their responses in comparison to the group's collective input before finalizing or revising their answers. The data analysis encompassed an examination of responses from questionnaire rounds 1 and 2. The median and interquartile range were used to gauge the significance of the identified factors. Experts exhibited consistent responses (median ≥ 3.5, interquartile range ≤ 1.5), though a 12.02% variation indicated divergent views. Consequently, the researcher finalized the questionnaire and summarized the findings. Round 1 data was collected from December 15, B.E. 2565 (2022), to March 18, B.E. 2566 (2023), and round 2 data was collected from April 15, B.E. 2566 (2023), to May 15, B.E. 2566 (2023). Results of the Study: 1) Definition and meaning of medication adherence in patients with NCDs in Thailand, Experts are highly to most highly agree, and have consensus across all six dimensions and 18-item checklist includes items ranging from 3.77 to 4.88 (IR = 0.61-1.38). 2) National drug-related policy: This encompasses both the national drug policy and the main national drug formulary, the Public Procurement and Supplies Administration Act B.E. 2560 (2017), as well as the policies and core regulations concerning the rights and costs of treatment and medication for chronic disease patients. Experts agree these impacts on the management of chronic disease medications in hospitals and the prescription of medications by physicians, ranging from a high to the highest level of impact and consistency across the two dimensions. Additionally, an 8-item checklist with items ranging from 3.78 to 4.63 (IR = 0.94-1.41). 3) The policy of the Near-home Medicine Pick-up Project, which allows patients with chronic illnesses to obtain medications from nearby over-the-counter pharmacies, has an impact on medication adherence. Experts agree that the policy shows a high to the highest level of impact and consistency across the six dimensions of the 16-item list (MD = 3.68-4.12, IR = 0.61-1.26). 4) National Policy on medicines, the National List of Essential Medicines Government Procurement and Supplies Management Act 2017 and universal health coverage policies and regulations related to rights and expenses for treatment and medicines of patients with NCDs, experts do not agree.