Semaglutide from Bench to Bedside: The Experimental Journey Towards a Transformative Therapy for Diabetes, Obesity and Metabolic Liver Disorders

Background/Objectives: Type 2 diabetes and obesity present escalating global health and economic challenges, highlighting the need for therapies that can effectively manage glycemic levels and reduce excess adiposity. Semaglutide, a glucagon-like peptide-1 receptor (GLP-1R) agonist available in subcutaneous or oral formulation, has quickly evolved from a theoretical concept to a crucial component of modern metabolic care. This review explores the comprehensive development journey of semaglutide, drawing on evidence from medicinal chemistry, animal studies, initial human trials, the pivotal SUSTAIN and STEP programs, and real-world post-marketing surveillance. Methods: We conducted a detailed analysis of preclinical data sets, Phase I–III clinical trials, regulatory documents, and pharmaco-epidemiological studies published between 2008 and 2025. Results: Through strategic molecular modifications, such as specific amino-acid substitutions and the addition of a C18 fatty-diacid side chain to enhance albumin binding, the half-life of the peptide was extended to approximately 160 h, allowing for weekly dosing. Studies in rodents and non-human primates showed that semaglutide effectively lowered blood glucose levels, reduced body weight, and preserved β-cells while maintaining a favorable safety profile. Phase I trials confirmed consistent pharmacokinetics and tolerability, while Phase II trials identified 0.5 mg and 1.0 mg once weekly as the most effective doses. The extensive SUSTAIN program validated significant reductions in HbA1c levels and weight loss compared to other treatments, as well as a 26% decrease in the relative risk of major adverse cardiovascular events (SUSTAIN-6). Subsequent STEP trials expanded the use of semaglutide to chronic weight management, revealing that nearly two-thirds of patients experienced a body weight reduction of at least 15%. Regulatory approvals from the FDA, EMA, and other regulatory agencies were obtained between 2017 and 2021, with ongoing research focusing on metabolic dysfunction-associated steatohepatitis, cardiovascular events, and chronic kidney disease. Conclusions: The trajectory of semaglutide exemplifies how intentional peptide design, iterative translational research, and outcome-driven clinical trial design can lead to groundbreaking therapies for complex metabolic disorders.