Background <p>Non-adherence to diabetes medication is associated with poor glycemic control and suboptimal benefits from prescribed medication, leading to worsening of the medical condition, comorbidities, reduced quality of life, higher healthcare costs, and increased mortality. This study aimed to assess the harmful effects of medication shortages and their association with medication adherence among patients with diabetes in the context of multiple crises in Lebanon.</p> Methods <p>A cross-sectional study was conducted among 430 type 1 and type 2 Lebanese diabetic patients attending primary healthcare centers, pharmacies, and private clinics. Participants were 18 years and older; non-Lebanese patients were excluded. Adherence to diabetes medications was measured using the Lebanese Medication Adherence Scale (LMAS-14) and the Harmful Impact of Medication Shortage (HIMS) score. All participants completed a self-report questionnaire, including sociodemographic and clinical profile variables. Univariate and multivariate analyses were carried out using SPSS version 28.</p> Results <p>Patients with lower education (8 years or less) were less adherent to medications than those with a university degree (21.00 vs. 17.00). Manual workers had less adherence to medication than non-manual workers (23.00 vs. 19.00). In addition, patients residing in Baalbeck, Beqaa, or Akkar, those who did not follow a diabetes-specific diet, smokers, and those not regularly testing their glycemia were less adherent to treatment. Most importantly, 36.3% of the total participants switched their medications due to their high cost and were less adherent to treatment. Patients unaware of DM as a disease had significantly lower medication adherence, similar to those who scored higher on the Harmful Impact of Medication Shortage.</p> Conclusion <p>This cross-sectional study identified suboptimal medication adherence among Lebanese adults with diabetes, with lower adherence associated with low socioeconomic status and barriers to care and medication access. These findings support targeted interventions to improve affordability, continuity of follow-up, and reliable access to medication, while warranting the conduct of longitudinal studies using objective adherence measures..</p> Trial registration <p>Not applicable.</p>