Semaglutide and the GLP-1 Receptor: What the Published Research Reports

Semaglutide is an acylated analogue of human glucagon-like peptide-1 (GLP-1) developed as a once-weekly GLP-1 receptor agonist [1]. The medicinal-chemistry programme that produced it reported two amino acid substitutions relative to human GLP-1 (Aib8, Arg34) together with derivatisation at lysine 26, a design intended to raise albumin affinity while retaining metabolic stability [1]. In that in vitro characterisation, GLP-1 receptor affinity was measured at 0.38 ± 0.06 nM, approximately three-fold lower than liraglutide, while albumin affinity was higher [1]. In the same programme, plasma half-life in mini-pigs — an animal model — was 46.1 h after intravenous administration, with a mean residence time of 63.6 h after subcutaneous administration [1]. Mechanistic reviews of the compound describe GLP-1 receptor agonism acting on glucose regulation and appetite pathways [2][3]. A review of the gut–brain and entero-pancreatic hormone literature places semaglutide within a class of agents whose weight-related effects are attributed to appetite and satiety signalling [4]. A separate review of GLP-1 receptor agonist gastrointestinal physiology in humans focuses on delayed gastric emptying, noting that slowed emptying contributes to post-prandial glucose responses in type 2 diabetes while also raising questions about intragastric retention of food before surgery or upper gastrointestinal endoscopy; the authors state that the evidence base for long-acting agents such as semaglutide is poor and call for further research [5]. A mechanistic review of metabolic dysfunction-associated steatotic liver disease summarised preclinical and clinical reports of reduced de novo lipogenesis via ChREBP and SREBP-1c signalling, altered adipose tissue mass, and changes in pro-inflammatory markers in GLP-1-expressing macrophages, but emphasised that GLP-1 receptor expression is absent in mouse and human liver, so the pathways described are interpreted as indirect and remain unresolved [6]. In human trials, reviews of the phase 3 programmes report that subcutaneous semaglutide produced reductions of approximately 15% of initial body weight at 68 weeks alongside changes in cardiometabolic risk factors and physical functioning [2]. A review of the STEP 1–5 trials described sustained weight reduction versus placebo, with gastrointestinal events as the most commonly reported adverse events, generally transient and mild-to-moderate [3]. Earlier narrative reviews traced the compound from phase 2 dose-finding work in participants with obesity but without type 2 diabetes to regulatory approval, and noted the availability of both subcutaneous and oral formulations [7][8]. Head-to-head human data are available against the dual GLP-1/GIP agonist tirzepatide. In the open-label phase 3b SURMOUNT-5 trial in adults with obesity but without type 2 diabetes, least-squares mean percent weight change at week 72 was −13.7% with semaglutide and −20.2% with tirzepatide, with mean waist circumference changes of −13.0 cm and −18.4 cm respectively; gastrointestinal adverse events were the most common in both groups and occurred mainly during dose escalation [9]. A retrospective cohort study using linked US electronic health record and dispensing data reported greater on-treatment weight reduction with tirzepatide than semaglutide at 3, 6, and 12 months, with similar rates of gastrointestinal adverse events between groups [10]. Cardiovascular, kidney, and heart-failure outcomes have been summarised from human trials. A review reported a 26% reduction in major adverse cardiovascular events in SUSTAIN-6 (HR 0.74; 95% CI 0.58–0.95), a 24% reduction in major kidney disease events in FLOW (HR 0.76; 95% CI 0.66–0.88), and a 20% reduction in major adverse cardiovascular events in SELECT among people with overweight or obesity and pre-existing cardiovascular disease (HR 0.80; 95% CI 0.72–0.90) [11]. A set of claims-based cohort studies emulating and then extending trial eligibility criteria in cardiometabolic heart failure with preserved ejection fraction reported a lower risk of the composite of heart-failure hospitalisation or all-cause mortality for semaglutide initiators versus a sitagliptin placebo proxy (HR 0.58; 95% CI 0.51–0.65), with no meaningful difference between tirzepatide and semaglutide (HR 0.86; 95% CI 0.70–1.06) [12]. Comparative work on oral administration continues. In the 52-week randomised, open-label, phase 3 ACHIEVE-3 trial in adults with type 2 diabetes inadequately controlled with metformin, the non-peptide oral GLP-1 receptor agonist orforglipron met non-inferiority and then superiority criteria against oral semaglutide for mean HbA1c change from baseline; gastrointestinal adverse events, discontinuations due to adverse events, and mean pulse-rate increase were more frequent with orforglipron than with oral semaglutide [13]. Safety reviews and surveillance datasets characterise the reported adverse-event profile. A narrative safety review of the SUSTAIN and PIONEER programmes concluded that reported events were mostly mild-to-moderate, transient gastrointestinal disturbances, with an increased risk of biliary disease (cholelithiasis), and noted that definitive conclusions on pancreatic and thyroid cancer could not be drawn because of low event incidence; the authors also flagged monitoring of existing diabetic retinopathy [14]. A global disproportionality analysis of the FAERS and VigiBase spontaneous-report databases found elevated reporting odds ratios for semaglutide and ischaemic optic neuropathy and diabetic retinopathy, along with retinal or vitreous detachment, haemorrhage, and retinal tear, and the authors framed these as pharmacovigilance signals requiring post-marketing surveillance rather than causal estimates [15]. A large propensity-score-matched community cohort study of patients with obesity reported higher observed risks of any psychiatric disorder, major depression, anxiety, and suicidal behaviour among GLP-1 receptor agonist users than matched non-users, and the authors called for prospective clinical trials to interpret the association [16]. Contextual literature covers the surrounding pipeline and use patterns. Pipeline reviews describe combinations of GLP-1 receptor agonism with GIP, glucagon, and amylin receptor agonists, including a co-formulation of semaglutide with the amylin analogue cagrilintide and the triple agonist retatrutide, positioning semaglutide as the current comparator for weight-related efficacy in these programmes [4][17]. A retrospective analysis of US commercial and Medicare Supplemental claims from 2018 to 2023 reported rising GLP-1 receptor agonist prescribing, with semaglutide accounting for a 60% share among users without a diabetes indication who had overweight or obesity [18]. A cohort-level Markov cost-effectiveness model built on SELECT trial data estimated an incremental cost-effectiveness ratio of $136,271 per quality-adjusted life year at US list price, with a lower estimate under an assumed rebate scenario [19]. A commentary in the aesthetic medicine literature reviewed reports of facial volume loss, skin laxity, and body-contour changes following rapid GLP-1-associated weight reduction and noted gaps in empirical data on these observations [20]. Taken together, the retrieved literature combines preclinical receptor-binding and animal pharmacokinetic characterisation [1], mechanistic hypotheses that the authors themselves describe as incompletely resolved [5][6], randomised human trial outcomes [9][13], observational human cohort and claims analyses [10][12][18], and hypothesis-generating surveillance signals [15][16].