Semaglutide is a synthetic, fatty-diacid-conjugated long-acting peptide developed by Novo Nordisk as a once-weekly agonist of the glucagon-like peptide-1 (GLP-1) receptor. It is the most extensively studied molecule in the incretin class, marketed clinically as Ozempic, Wegovy and Rybelsus, and it established the modern template for durable metabolic effect through a single, highly selective receptor arm — appetite suppression, glucose-dependent insulin secretion and slowed gastric emptying combined in one long-acting analogue.
Semaglutide is a once-weekly GLP-1 receptor agonist developed by Novo Nordisk and marketed clinically as Ozempic, Wegovy and Rybelsus. It is the most extensively studied compound in the incretin class. In the Phase 3 STEP-1 obesity trial (NEJM, 2021; n=1,961, 68 weeks) it produced a mean -14.9% body-weight change versus -2.4% with placebo, and in the landmark SELECT cardiovascular-outcomes trial (NEJM, 2023; n=17,604) it reduced major adverse cardiovascular events by 20% in adults with obesity and established cardiovascular disease but without diabetes. It has a ~7-day half-life (~165 h) owing to C18 fatty-diacid conjugation, is supplied as a lyophilised powder reconstituted with bacteriostatic water, and is provided by RS Bio Labs strictly as an in vitro research reagent — not for human use. Research-grade Semaglutide is available in four strengths at ≥99% purity; see the buy Semaglutide UK page.
Semaglutide is a synthetic 31-amino-acid peptide engineered by Novo Nordisk to act as a potent, long-acting agonist of a single metabolic receptor: the glucagon-like peptide-1 receptor (GLP-1R). Structurally it is an analogue of native human GLP-1, modified at two key positions and conjugated to a C18 fatty-diacid chain that confers its extended, once-weekly duration of action. Because it engages one receptor with high selectivity, it is described in the literature as a "GLP-1 receptor agonist" — the foundational class from which the dual agonist Tirzepatide and the triple agonist Retatrutide were subsequently developed.
Marketed clinically as Ozempic (type 2 diabetes), Wegovy (weight management) and Rybelsus (an oral formulation), semaglutide is the single most widely prescribed and most deeply characterised molecule in the entire incretin field. Its clinical evidence base is the broadest of any compound in the class, spanning glycaemic control, weight management and — uniquely — hard cardiovascular outcomes in people without diabetes. For research purposes it serves as the reference standard against which every newer multi-receptor agonist is benchmarked.
As of 2026 semaglutide is an FDA-approved medicine in its licensed clinical formulations. However, RS Bio Labs supplies it strictly as a research reagent for in vitro laboratory work — not as a medicine and not for human use. Researchers looking to buy Semaglutide in the UK can obtain it in four strengths, each third-party HPLC tested to ≥99% purity.
Semaglutide is the product of a sustained incretin-engineering programme at Novo Nordisk. The scientific lineage runs from native glucagon-like peptide-1 — a gut hormone with a half-life of only a couple of minutes — through the first short-acting analogue liraglutide (once-daily), and finally to semaglutide, in which further structural modification extended the duration of action out to a full week.
The molecule's design solved the central problem of native GLP-1: its near-instant degradation by the enzyme dipeptidyl peptidase-4 (DPP-4) and rapid renal clearance. Novo Nordisk substituted the amino acid at position 8 to resist DPP-4 cleavage, and attached a C18 fatty-diacid chain via a linker that promotes strong, reversible binding to serum albumin. Albumin binding shields the peptide from degradation and slows its elimination, transforming a compound that lasts minutes into one that lasts roughly a week.
The clinical programme unfolded across two major franchises. The SUSTAIN trials established efficacy and cardiovascular safety in type 2 diabetes, and the STEP trials established weight-management efficacy in obesity. The programme then culminated in SELECT (ClinicalTrials.gov registration), a dedicated cardiovascular-outcomes trial that demonstrated benefit on hard endpoints in people with obesity and cardiovascular disease but without diabetes — an evidence milestone no other incretin compound had reached at the time.
Semaglutide is a single peptide molecule that binds and activates one class B G-protein-coupled receptor: the GLP-1 receptor. Although it engages only one target, that receptor is expressed across several tissues — the pancreas, the brain's appetite centres and the gut — so a single agonist produces a coordinated, multi-tissue metabolic response. The three principal arms of that response are summarised below.
The elegance of semaglutide's design lies in its selectivity: because GLP-1R activation promotes insulin secretion only when blood glucose is elevated, the glucose-lowering effect is largely self-limiting, which distinguishes it from older insulin-secretagogue drugs. The molecule itself is a fatty-diacid-conjugated (C18) long-acting peptide; the diacid tail promotes reversible albumin binding, which is what gives semaglutide its extended, once-weekly duration of action. For a broader treatment of how the GLP-1 arm differs from the GIP and glucagon arms added in later multi-agonists, see our guide to GLP-1 vs GIP vs glucagon agonists.
Semaglutide has the deepest clinical evidence base of any compound in the incretin class, spanning glycaemic control, weight management and hard cardiovascular outcomes. The landmark readouts are summarised below, followed by the individual trial cards.
| Trial / population | Publication | n | Headline result |
|---|---|---|---|
| Phase 3 · Obesity (STEP-1) | NEJM, 2021 | 1,961 | -14.9% mean weight change vs -2.4% placebo (68 wk) |
| CV outcomes · Obesity + CVD, no diabetes (SELECT) | NEJM, 2023 | 17,604 | ~20% reduction in major adverse cardiovascular events |
| CV outcomes · Type 2 diabetes (SUSTAIN-6) | NEJM, 2016 | 3,297 | ~26% reduction in the primary CV composite endpoint |
Semaglutide's defining pharmacokinetic feature is its terminal half-life of approximately seven days (around 165 hours). This is a direct consequence of the molecule's C18 fatty-diacid conjugation, which drives strong, reversible binding to serum albumin. Albumin binding acts as a circulating reservoir, slows renal clearance, and shields the peptide from rapid enzymatic degradation — the same design principle used across the modern long-acting incretin class.
A ~7-day half-life supports a once-weekly research schedule. As with any compound dosed at roughly one half-life intervals, plasma concentrations accumulate over successive administrations and approach steady state after about four to five half-lives — on the order of four to five weeks. This accumulation behaviour is the reason published protocols use gradual dose escalation: titrating upward over several weeks allows tolerance to the gastrointestinal effects to develop as concentrations rise.
| Parameter | Value (approx.) | Note |
|---|---|---|
| Terminal half-life | ~7 days (~165 h) | Fatty-diacid/albumin driven |
| Research schedule | Once weekly | ~1 half-life dosing interval |
| Time to steady state | ~4–5 weeks | ~4–5 half-lives |
| Molecular weight | ~4,114 Da | 31-aa peptide + C18 diacid tail |
| Elimination | Proteolysis + renal | Slowed by albumin binding |
As a lyophilised (freeze-dried) powder, Semaglutide is highly stable. Removing water from the formulation dramatically slows the chemical degradation pathways — hydrolysis, deamidation, oxidation and aggregation — that shorten a peptide's shelf life in solution. Sealed, protected from light and kept cool, lyophilised semaglutide retains its integrity over long periods.
Stability falls once the powder is reconstituted. In solution the peptide becomes susceptible to gradual hydrolysis and to physical stresses such as agitation (which can cause aggregation and foaming) and repeated freeze–thaw cycles (which mechanically damage peptide structure). Heat and light accelerate degradation in both states. In practical terms this means the lyophilised vial is the storage-stable form, and the reconstituted solution should be treated as a shorter-lived working stock — see Storage and Reconstitution below.
Correct storage preserves both the mass and the biological integrity of the compound. The guidance below reflects standard best practice for lyophilised research peptides.
| State | Temperature | Approx. shelf life | Notes |
|---|---|---|---|
| Lyophilised | −20 °C (freezer) | Months to years | Best long-term option; protect from light |
| Lyophilised | 2–8 °C (fridge) | Weeks to months | Fine for medium-term storage |
| Lyophilised | Room temperature | Days (transit) | Tolerates brief shipping periods |
| Reconstituted | 2–8 °C (fridge) | ~4–6 weeks | Bacteriostatic water aids stability; keep dark |
| Reconstituted | Frozen | Avoid | Freeze–thaw degrades the peptide |
Label reconstituted vials with the date of preparation, minimise exposure to light and heat, and avoid repeatedly warming and cooling a working stock. Allow refrigerated vials to return toward room temperature before handling to reduce condensation.
The following describes standard laboratory technique for preparing a research stock solution from a lyophilised vial. It is not guidance for human use of any kind. For a fully worked walkthrough with more dilution examples, see our reconstitution calculator.
Reconstitution simply means dissolving the freeze-dried powder into solution. The standard diluent for a multi-use research vial is bacteriostatic water (water with 0.9% benzyl alcohol, which suppresses microbial growth). You will also need a sterile syringe and alcohol wipes. Technique matters: wipe the vial stopper, draw the chosen volume of bacteriostatic water, and add it slowly down the inner glass wall rather than squirting it directly onto the powder. Let the peptide dissolve, swirl gently, and never shake — agitation causes foaming and can damage the peptide.
Concentration is simply the mass of peptide divided by the volume of water added. Adding more water gives a lower concentration:
| Vial | Bacteriostatic water added | Resulting concentration |
|---|---|---|
| 2 mg | 1 ml | 2 mg/ml |
| 5 mg | 1 ml | 5 mg/ml |
| 5 mg | 2 ml | 2.5 mg/ml |
| 10 mg | 1 ml | 10 mg/ml |
| 10 mg | 2 ml | 5 mg/ml |
Once reconstituted, store the vial refrigerated at 2–8 °C and use it within a few weeks (see Storage). Maintain sterility throughout and label the vial with the concentration and preparation date.
Semaglutide sits at the foundation of the incretin "agonism ladder" — the single-receptor compound from which the dual and triple agonists were built. The table below places it against the other most-studied metabolic research peptides by receptor targets and headline trial effect. For the mechanistic detail behind these classes, see GLP-1 vs GIP vs glucagon.
| Compound | Receptor targets | Class | Peak trial weight change | Half-life |
|---|---|---|---|---|
| Semaglutide | GLP-1 | Mono | ~14.9% (Ph3 STEP-1, 68 wk) | ~7 days |
| Tirzepatide | GIP + GLP-1 | Dual | ~22.5% (Ph3, 72 wk) | ~5 days |
| Retatrutide | GIP + GLP-1 + Glucagon | Triple | ~24.2% (Ph2, 48 wk) | ~6 days |
| Mazdutide | GLP-1 + Glucagon | Dual | ~14% (Ph3, 48 wk) | Weekly |
| Survodutide | GLP-1 + Glucagon | Dual | MASH-focused Ph2 | ~6 days |
The pattern is consistent: engaging more complementary receptor systems has raised the ceiling on effect size at each step beyond semaglutide. But semaglutide's advantage is depth of evidence, not breadth of mechanism — it is the only compound in the class with a completed hard-endpoint cardiovascular-outcomes trial in a non-diabetic obesity population, which is why it remains the reference standard. To compare live pricing and strengths, see the buy Semaglutide UK and buy Retatrutide UK pages.
The findings above are drawn from the following peer-reviewed publications and trial registrations. Links open on the publisher or registry site.