Insulin Initiation in Type 2 Diabetes Mellitus: When, Why and How to Start Insulin Therapy

Abstract

ackground: Type 2 diabetes mellitus (T2DM) is fundamentally characterised by a progressive, inexorable decline in pancreatic beta-cell function superimposed on peripheral insulin resistance. Although initial management relies on lifestyle modifications and non-insulin antihyperglycemic therapies, a substantial proportion of patients eventually require exogenous insulin to achieve and maintain optimal glycemic targets. Aims: This review synthesises current clinical evidence, international consensus guidelines, and recent therapeutic breakthroughs to provide an operational framework on the clinical triggers ("when"), physiological rationales ("why"), and practical algorithms ("how") of initiating insulin therapy. Methods: A comprehensive literature search of electronic databases, including PubMed, MEDLINE, and Embase, was conducted to identify English-language, peer-reviewed literature, clinical guidelines, and landmark trials concerning insulin therapy in T2DM. This review evaluates data from foundational clinical trials (UKPDS, ACCORD, ADVANCE, and the GRADE study) alongside current consensus recommendations from the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD). Literature tracking clinical thresholds for initiation, comparative data on traditional insulin regimens (basal, biphasic, basal-bolus), and Phase 3 clinical trial data for once-weekly basal insulins and digital health technologies published between 2019 and 2026 were extracted and evaluated. Conclusions: Overcoming clinical inertia requires proactive clinician intervention, structured patient education to address psychological insulin resistance, and the early adoption of advanced monitoring technologies. Timely and tailored implementation of insulin therapy remains a cornerstone in altering the long-term microvascular and macrovascular trajectory of patients with T2DM. Keywords: Type 2 Diabetes Mellitus; Insulin Initiation; Basal Insulin; Clinical Inertia; Hypoglycemia.