Semaglutide

What semaglutide is

Semaglutide is a synthetic, single-chain peptide of 31 amino acids that acts as a selective agonist at the glucagon-like peptide-1 receptor (GLP-1R). It is an analogue of the native hormone fragment GLP-1(7-37), developed at Novo Nordisk as a once-weekly successor to liraglutide, and the discovery work is set out in the 2015 paper by Lau and colleagues in the Journal of Medicinal Chemistry [1]. The design history, and the reasoning behind each structural choice, is reviewed by Knudsen and Lau [2].

Three changes separate semaglutide from the native peptide. The alanine at position 8 is replaced by 2-aminoisobutyric acid (Aib), a non-natural residue that protects the N-terminus against cleavage by dipeptidyl peptidase-4 (DPP-4), the enzyme that inactivates native GLP-1 within minutes of release [1, 2]. The lysine at position 34 is replaced by arginine, so that only one lysine remains for acylation [2]. And the lysine at position 26 carries a C18 fatty diacid attached through a linker made of one γ-glutamyl unit and two 8-amino-3,6-dioxaoctanoic acid (OEG) units [1, 2]. The diacid binds reversibly to serum albumin, which shields the peptide from renal clearance and enzymatic attack and extends its circulating half-life; the discovery paper reports a human half-life of around 165 hours, and the licensed product's summary of product characteristics gives it as approximately one week [1]. That albumin binding is why the injected clinical formulation is dosed once weekly.

The lipid and linker were the main variables in the medicinal chemistry programme. Lau and colleagues report that the C18 diacid with the γGlu–2×OEG linker gave the best combination of albumin affinity and receptor potency among the derivatives tested, and that semaglutide's affinity for the GLP-1 receptor (0.38 nM in their assay) was around three-fold lower than liraglutide's, a trade-off accepted for the much longer duration of action [1]. The Arg34 substitution had no apparent effect on receptor binding [2].

The molecule is a white to off-white lyophilised powder in its research presentation. The reference identifiers are in the table below; the values on any given batch certificate should agree with them within the precision of the method used.

Residue positions follow the conventional GLP-1(7-37) numbering used in the literature, in which the first residue of the active fragment is histidine 7. Counted from the N-terminus of the peptide chain itself, Aib8 is the second residue, Lys26 the twentieth and Arg34 the twenty-eighth.

How the literature describes its mechanism

GLP-1 is an incretin hormone released by intestinal L-cells after a meal. Acting through the GLP-1 receptor, a class B G-protein-coupled receptor, it potentiates glucose-dependent insulin secretion from pancreatic β-cells, suppresses glucagon release, slows gastric emptying and reduces appetite through receptors in the brain [2]. Native GLP-1 has a plasma half-life of a few minutes, which made it unusable as a drug and set the central problem for the field: how to keep the receptor activity of the native peptide while extending its residence in the circulation [2].

Semaglutide answers that problem with protraction by albumin binding. In plasma, the great majority of the peptide is bound to albumin, and only the free fraction is available to activate the receptor. Knudsen and Lau describe the design tension this creates: stronger albumin binding gives a longer half-life but leaves less free peptide, so the diacid and linker had to be tuned so that potency at the receptor was preserved [2]. The receptor pharmacology itself is that of a full GLP-1 receptor agonist; semaglutide does not act at the GIP or glucagon receptors, which distinguishes it from the dual and triple agonists discussed in the related-compounds section.

For an in-vitro programme, the relevant readouts are cAMP accumulation in cells expressing the GLP-1 receptor, receptor binding by displacement of a labelled ligand, and insulin secretion from isolated islets under varying glucose. Two methodological points matter for semaglutide in particular. First, potency values depend strongly on the albumin content of the assay medium, because albumin sequesters the peptide; the discovery paper reports receptor affinities measured both with and without albumin for this reason, and figures from different papers should not be compared without checking the assay conditions [1]. Second, the lipid chain makes the molecule adsorb to plastics and some filter membranes, so low-binding labware is advisable where accurate concentrations are needed.

The clinical research record

Semaglutide has been studied in some of the largest clinical trial programmes in metabolic medicine. The main series are SUSTAIN, in type 2 diabetes with the subcutaneous once-weekly formulation; PIONEER, in type 2 diabetes with the oral formulation; STEP, in obesity and overweight; and SELECT, a cardiovascular outcomes trial in people with obesity but without diabetes. The headline findings from the primary publications of four landmark trials are summarised here as trial facts.

SUSTAIN-6 (Marso et al., New England Journal of Medicine, 2016) randomised 3,297 adults with type 2 diabetes at high cardiovascular risk to semaglutide 0.5 mg or 1.0 mg once weekly or placebo, with a median follow-up of 2.1 years. The primary composite of cardiovascular death, non-fatal myocardial infarction or non-fatal stroke occurred in 6.6% of the semaglutide group and 8.9% of the placebo group, a hazard ratio of 0.74 (95% CI 0.58–0.95), establishing non-inferiority. Rates of diabetic retinopathy complications were higher with semaglutide (3.0% against 1.8%), a finding that has been discussed in the literature since [3].

STEP 1 (Wilding et al., New England Journal of Medicine, 2021) enrolled 1,961 adults with obesity, or overweight with at least one weight-related condition, without diabetes, and compared semaglutide 2.4 mg once weekly with placebo, both alongside lifestyle intervention, over 68 weeks. Mean body-weight change was −14.9% with semaglutide against −2.4% with placebo, an estimated treatment difference of −12.4 percentage points; 86.4% of the semaglutide group lost at least 5% of body weight compared with 31.5% of the placebo group [4].

SELECT (Lincoff et al., New England Journal of Medicine, 2023) enrolled 17,604 adults aged 45 or over with pre-existing cardiovascular disease and a body-mass index of 27 or more, without diabetes, and randomised them to semaglutide 2.4 mg once weekly or placebo with a mean follow-up of 39.8 months. The primary composite of cardiovascular death, non-fatal myocardial infarction or non-fatal stroke occurred in 6.5% of the semaglutide group and 8.0% of the placebo group, a hazard ratio of 0.80 (95% CI 0.72–0.90) [5].

Across these programmes the most frequently reported adverse events were gastrointestinal: nausea, diarrhoea, vomiting and constipation, mostly mild to moderate, transient and concentrated during dose escalation. In STEP 1, 4.5% of the semaglutide group discontinued because of gastrointestinal events against 0.8% of the placebo group [4].

For the laboratory reader, the significance of this record is that semaglutide has become the reference compound of the incretin class. It is the comparator against which tirzepatide was tested in SURPASS-2 and the GLP-1 component of the cagrilintide combination studied as CagriSema, and its pharmacology, pharmacokinetics and degradation behaviour are unusually well documented in the public domain.

Regulatory status in the United Kingdom

Semaglutide is the active ingredient of three licensed prescription-only medicines in the UK: Ozempic (subcutaneous, for type 2 diabetes), Wegovy (subcutaneous, for weight management under specified conditions) and Rybelsus (oral tablets, for type 2 diabetes), all authorised by the MHRA and held by Novo Nordisk. BuyUK Peptides does not supply any of those medicines, and the research-grade peptide sold here is not a medicine, is not manufactured or presented as one, and carries no therapeutic claim.

Research-grade semaglutide is supplied as a chemical for in-vitro laboratory use under the Terms of Sale. It is not for human or veterinary administration. Purchasers must be 18 or over and are responsible for ensuring their use of the material complies with the laws and institutional rules that apply to them. Our guide to the UK rules on research compounds sets this out in more detail.

Handling, storage and stability

Semaglutide is supplied lyophilised, sealed under nitrogen in a glass vial with a rubber stopper and an aluminium flip-off crimp, in 10 mg, 15 mg and 20 mg presentations. In that state it is stable for extended periods when kept cold and dark.

Sealed vial. Store at 2–8 °C for routine use. For storage beyond a few months, −20 °C or below is preferable. Protect from light. Avoid repeated freeze–thaw cycles; take the vial out once and keep it at the working temperature from then on. Allow a refrigerated vial to reach room temperature before opening, so that moisture does not condense onto the cake.

Reconstitution. For most in-vitro work the compound is reconstituted in sterile bacteriostatic water, sterile water for injection, or a buffer appropriate to the assay. Add the solvent slowly down the side of the vial rather than onto the cake, and swirl gently; do not shake, because peptides with a hydrophobic lipid chain can aggregate or foam under agitation. A lipidated peptide dissolves more slowly than a short unmodified fragment; a minute or two of gentle swirling is normal. Semaglutide has a free C-terminal carboxylate and an acidic diacid side chain, so it dissolves most readily at neutral or mildly basic pH and tends to come out of solution as the pH falls towards its isoelectric point. The reconstitution calculator gives the volume to add for a target concentration.

Reconstituted solution. Keep at 2–8 °C and protect from light. Lipidated GLP-1-class peptides are generally stable in aqueous solution at refrigerator temperature for several weeks, and the UK summary of product characteristics for the licensed injectable supports storage of the clinical solution for six weeks once in use, below 30 °C or refrigerated, with the instruction not to freeze it and not to use it if it has been frozen. For a research solution the conservative practice is to use it within 28 days and to discard it if it becomes cloudy or shows particles. Solutions should not be frozen after reconstitution unless the specific buffer has been validated for that.

Solubility. Semaglutide is soluble in water at the concentrations used in research. The C18 diacid side chain makes the molecule amphipathic, so very high concentrations and low pH both encourage self-association, and the licensed formulations are buffered at pH 7.4 for this reason. Where a solution must be filtered, use a low-binding membrane (PES or PVDF rather than nylon), because the lipid chain adsorbs to some filter materials.

What a sound certificate for semaglutide looks like

Every batch we release carries an independent certificate of analysis, and the figures from it are transcribed on the product page and in the certificate register. For semaglutide, a certificate should contain the following, and a reader should be able to check each item against this monograph.

Purity by RP-HPLC. Reversed-phase HPLC on a C18 column with UV detection, usually at 214 or 220 nm, reports purity as the area of the main peak as a percentage of all integrated peaks. A good batch of semaglutide shows a single dominant peak with purity of 99% or above. Small late-eluting peaks may represent oxidised species or diastereomers formed during synthesis; a large early-eluting shoulder is more often a truncated or deacylated sequence and should prompt questions. Because the lipid chain dominates the retention behaviour, a batch of semaglutide elutes considerably later than an unacylated GLP-1 fragment under the same gradient, and a peak at the retention time of the unacylated peptide is a specific impurity worth asking about.

Identity by LC-MS. Electrospray mass spectrometry confirms that the main peak has the expected mass. For semaglutide the average molecular weight is 4113.58 Da and the monoisotopic mass 4111.12 Da. Electrospray produces multiply charged ions, so a certificate may report the deconvoluted mass, the most abundant charge state, or both. The observed mass should agree with the theoretical value to within a few tenths of a dalton for a deconvoluted result.

Net peptide content. Lyophilised peptides contain bound water and counter-ions, typically trifluoroacetate from purification, so the mass of powder in the vial is more than the mass of peptide. Net peptide content, where reported, expresses the fraction that is actual peptide, and it matters for preparing solutions of accurate concentration.

Endotoxin. Where the batch has been tested, a limulus amoebocyte lysate (LAL) result is reported in endotoxin units per milligram. This is relevant to cell-based assays, where endotoxin contamination can confound results.

Our guide to reading a certificate of analysis goes through a complete report line by line.

Related compounds

Semaglutide is the selective GLP-1 receptor agonist against which the newer multi-receptor peptides are compared. Tirzepatide is a dual GIP and GLP-1 receptor agonist built on the GIP backbone and lipidated with a C20 diacid; semaglutide 1 mg was its comparator in SURPASS-2. Retatrutide adds glucagon receptor agonism to GIP and GLP-1 activity, making it a triple agonist. Cagrilintide is a long-acting amylin analogue that has been studied in combination with semaglutide. The structural and pharmacological differences between them are the subject of our GLP-1 family comparison. semaglutide and tirzepatide are compared head to head, including the SURMOUNT-5 result.

Frequently asked questions

Is research-grade semaglutide the same molecule as the licensed medicines? The chemical structure is the same peptide. The research material is supplied as a lyophilised powder, is not manufactured under a marketing authorisation, is not formulated with the excipients of the licensed products, is not sterile unless the certificate says so, and is not for human or veterinary use.

Why do papers number the residues from 7 rather than 1? Convention in the GLP-1 literature uses the numbering of the proglucagon-derived peptide GLP-1(1-37), in which the biologically active fragment begins at histidine 7. Aib8, Lys26 and Arg34 are positions in that scheme. Counted along the 31-residue chain they are residues 2, 20 and 28.

Why does the certificate quote a different mass from the formula weight? Electrospray results are often reported as a monoisotopic mass or a particular charge state rather than the average molecular weight. Both are valid; the certificate should say which it is reporting.

Why is semaglutide supplied in milligram quantities rather than by activity? It is a defined synthetic chemical, so it is characterised by mass and purity. Biological activity is determined by the researcher in their own assay.

How long does a sealed vial last? Lyophilised peptides of this class are stable for years at −20 °C and for many months at 2–8 °C. The batch certificate reports the test date; the storage guidance on this page applies from receipt.

References

1. Lau J, Bloch P, Schäffer L, et al. Discovery of the once-weekly glucagon-like peptide-1 (GLP-1) analogue semaglutide. Journal of Medicinal Chemistry. 2015;58(18):7370–7380. doi:10.1021/acs.jmedchem.5b00726.
2. Knudsen LB, Lau J. The discovery and development of liraglutide and semaglutide. Frontiers in Endocrinology. 2019;10:155. doi:10.3389/fendo.2019.00155. PMID 31031702.
3. Marso SP, Bain SC, Consoli A, et al. Semaglutide and cardiovascular outcomes in patients with type 2 diabetes (SUSTAIN-6). New England Journal of Medicine. 2016;375(19):1834–1844. doi:10.1056/NEJMoa1607141. PMID 27633186.
4. Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). New England Journal of Medicine. 2021;384(11):989–1002. doi:10.1056/NEJMoa2032183. PMID 33567185.
5. Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and cardiovascular outcomes in obesity without diabetes (SELECT). New England Journal of Medicine. 2023;389(24):2221–2232. doi:10.1056/NEJMoa2307563.

This monograph summarises the published literature for laboratory researchers. It is not medical advice, and nothing on this site is for human or veterinary use.