Semaglutide

What Is Semaglutide?

Semaglutide is a modified human glucagon-like peptide-1 (GLP-1) analogue that activates the GLP-1 receptor. It was developed by Novo Nordisk using the company’s protein-acylation technology and was first approved for type 2 diabetes.^[1]

GLP-1 is a gut-derived incretin hormone, and semaglutide belongs to the class of GLP-1 receptor agonists that also includes liraglutide and dulaglutide. In clinical studies, semaglutide lowers blood glucose by stimulating insulin release and also lowers body weight.^[1] It has been tested as monotherapy in type 2 diabetes and, in a separate program, for weight management in people with overweight or obesity.^[2][3]

Semaglutide has been developed in both subcutaneous and oral formulations, studied in the SUSTAIN and PIONEER trial programs respectively, while the STEP program examined it in obesity.^[4] Because its clinical record is large, semaglutide is often the comparator against which newer incretin-based molecules are measured.

Chemical Structure and Molecular Identity

Semaglutide is a 31-residue linear peptide built on the human GLP-1(7-37) sequence, with two amino-acid substitutions and a fatty-acid side chain. PubChem (CID 56843331) lists the molecular formula as C187H291N45O59 and the molecular weight as 4114 g/mol; the CAS Registry Number is 910463-68-2.

Structural features

• Position 8: alpha-aminoisobutyric acid (Aib) replaces the native alanine, directly after the N-terminal histidine.
• Position 34: arginine replaces the native lysine, leaving lysine 26 as the only lysine.
• Lipidation: the lysine 26 side chain carries an octadecanedioic acid (C18 diacid) attached through a gamma-glutamic acid spacer and two 8-amino-3,6-dioxaoctanoic acid linkers.
• Termini: a free N-terminal histidine and a free C-terminal glycine carboxylic acid.

The acylated side chain reflects the protein-acylation approach used in the molecule’s design.^[1] A systematic review of 17 human pharmacokinetic studies reported a long elimination half-life and a predictable pharmacokinetic profile, with exposure rising with dose for both oral and subcutaneous forms.^[5] Because the Aib residue is non-coded, semaglutide’s sequence cannot be written entirely in standard one-letter amino-acid code.

Research History and Development

Semaglutide moved from type 2 diabetes trials to obesity trials over roughly five years, with approvals in both areas. Its first regulatory approval, for type 2 diabetes, came in the US, Puerto Rico and Canada, with a positive opinion in the EU at the same time.^[1]

Type 2 diabetes trials

SUSTAIN 1 was a double-blind, placebo-controlled phase 3a trial at 72 sites in eight countries. It tested semaglutide monotherapy over 30 weeks in treatment-naive adults with type 2 diabetes managed by diet and exercise, with change in HbA1c as the primary endpoint and change in body weight as the confirmatory secondary endpoint.^[2] SUSTAIN 7, an open-label phase 3b trial in 1,201 adults on metformin at 194 sites in 16 countries, compared two dose levels of semaglutide head-to-head with two dose levels of dulaglutide over 40 weeks.^[6]

Obesity trials and further development

The STEP program evaluated semaglutide for weight management. STEP 2 enrolled 1,210 adults with overweight or obesity and type 2 diabetes from 149 clinics in 12 countries and compared a higher dose with the dose approved for diabetes and with placebo over 68 weeks.^[3] Results from the SUSTAIN, PIONEER and STEP programs led to FDA approval of semaglutide for weight loss.^[4] At the time of its first approval, clinical development was also under way in non-alcoholic steatohepatitis and non-alcoholic fatty liver disease.^[1]

Mechanisms Studied in Research

Semaglutide works by activating GLP-1 receptors, which stimulates insulin release and reduces food intake. Rodent studies suggest that its weight effects depend largely on GLP-1 receptor populations in the brain.^[1][7]

Central nervous system pathways in rodents

In rodent studies, semaglutide changed food preference, reduced food intake and caused weight loss without decreasing energy expenditure. Labeled semaglutide reached the brainstem, septal nucleus and hypothalamus but did not cross the blood-brain barrier. Instead it interacted with the brain through the circumventricular organs and selected sites next to the ventricles.^[7]

The same study found c-Fos activation in 10 brain areas, including the lateral parabrachial nucleus, a region without direct GLP-1 receptor contact that is linked to meal termination. Transcriptomic analysis in rats showed increased prolactin-releasing hormone and tyrosine hydroxylase in the area postrema.^[7]

Cardiac models

In a mouse model of doxorubicin-induced cardiotoxicity, semaglutide improved cardiac function measured by echocardiography and hemodynamic monitoring. In vitro experiments indicated that it reduced mitochondrial BNIP3 expression via the PI3K/AKT pathway, and heart-specific BNIP3 overexpression abolished the protective effect.^[8]

Key Findings From Published Studies

Human trials and meta-analyses report that semaglutide reduces body weight and glycated hemoglobin (HbA1c) compared with placebo, with gastrointestinal adverse events as the most frequent side effects.^[3][9] The table summarizes key quantitative results reported in the source abstracts.

Body weight and composition

A systematic review of six studies in 1,541 adults with overweight or obesity found that weight reduction came mainly from fat mass. Lean-mass losses ranged from almost 0% to 40% of total weight lost and were most evident in larger trials, although the proportion of lean mass relative to total body mass increased.^[11]

Cardiovascular outcomes

The cardiovascular meta-analysis also reported relative risks of 0.24 for heart-failure hospitalization, 0.76 for non-fatal myocardial infarction and 0.76 for coronary revascularization, and 0.65 for stroke in patients with diabetes.^[10]

Safety signals

In the meta-analysis of adults without diabetes, gastrointestinal adverse events were 1.59 times more likely with semaglutide, discontinuation due to adverse events was 2.19 times more likely, and serious adverse events, mostly gastrointestinal and hepatobiliary such as acute pancreatitis and cholelithiasis, were 1.60 times more likely.^[9] A retrospective matched cohort study of 16,827 patients seen by neuro-ophthalmologists examined whether semaglutide prescription was associated with nonarteritic anterior ischemic optic neuropathy (NAION).^[12] A narrative review of six observational studies covering 480,825 adults on GLP-1 receptor agonists, including semaglutide, reported vitamin D deficiency in 7.5% at 6 months and 13.6% at 12 months and lower ferritin than in SGLT2 inhibitor users, though causality could not be established.^[13]

Because semaglutide is a 4.1 kDa acylated peptide, HPLC purity and mass-spectrometry certificates of analysis are the practical way to verify a research sample's identity.

Regulatory and Research Status

Semaglutide is an FDA-approved medicine, referred to here only by its generic name. It was first approved for type 2 diabetes and later approved for weight management based on the SUSTAIN, PIONEER and STEP programs.^[1][4]

Research continues on pharmacokinetics in specific populations, on body composition during weight loss, and on safety signals identified in observational data.^[5][11][12] Reviewers note that most nutritional findings come from observational datasets and call for further study.^[13]

Outside its approved medical uses and registered clinical trials, material described as semaglutide is intended for laboratory research only. This page summarizes published findings and does not provide guidance on human use.