<p><i>Scoparia dulcis</i> L., Plantaginaceae, is a medicinal plant with antidiabetic properties and traditionally used, which could be a complementary treatment to improve adherence in the management of type 2 diabetes mellitus and glycemic control. This study investigates the effects of <i>S. dulcis</i> on treatment adherence and glycemic outcomes in adults with type 2 diabetes mellitus. This was a randomized, double-blind, placebo-controlled, pilot clinical trial. Participants were randomized to receive <i>S. dulcis</i> capsules or a placebo for 6 months. Medication adherence, HbA1c levels, insulin dosage, inflammatory markers, and lipid profile were monitored. A chemical profile of <i>S. dulcis</i> was conducted using HPLC, and the main compound was determined by ¹H and ¹³C NMR experiments. Among the 30 enrolled participants, adherence rates were highly variable, with approximately 50% of patients taking less than 80% of their prescribed doses. There was no significant difference in adherence between the intervention and placebo groups. No significant changes in HbA1c levels or other metabolic parameters were observed over time. Scutellarin is the plant’s major bioactive compound. Supplementation with <i>S. dulcis</i> did not enhance medication adherence or significantly improve glycemic control in type 2 diabetes mellitus patients. The findings highlight the complexities of adherence in chronic disease management.</p> Graphical Abstract <p></p>