A cross-sectional survey of 358 patients was conducted among type 2 diabetes patients recruited at medical institutions or via an online research company. Medication adherence was measured using the 8-item Morisky Medication Adherence Scale (MMAS-8). Univariate and multivariate regression analyses of glycosylated hemoglobin (HbA1c) were performed in addition to assessing demographic and disease characteristics and MMAS-8. In conclusion, medication adherence as measured by the MMAS-8 score independently contributes to altering the HbA1c level in the range of 1.12 %. The number of medications prescribed and insulin use are also related to HbA1c.