What semaglutide is and how it works
Semaglutide is a synthetic analogue of glucagon-like peptide-1, the gut hormone released by intestinal L-cells after a meal. The natural hormone is a fine signal and a poor drug: circulating GLP-1 is cut in half within about two minutes by the enzyme dipeptidyl peptidase-4. Semaglutide keeps the GLP-1(7-37) backbone and changes three things about it.
Position 8, the residue DPP-4 cleaves behind, is replaced by alpha-aminoisobutyric acid (Aib), which the enzyme cannot process. A C18 fatty diacid is attached to the lysine at position 26 through a short linker; that chain binds reversibly to serum albumin, so most of the peptide in the bloodstream travels as cargo on a protein too large for the kidney to filter. Arginine in place of lysine at position 34 removes the competing attachment site, so the fatty acid ends up in one place rather than two. Together they give an elimination half-life of roughly a week, hence the once-weekly injection.
GLP-1R is a class B G-protein-coupled receptor, and its effects are distributed rather than local. On the pancreatic beta cell it amplifies insulin release only when glucose is already elevated, which is why GLP-1 agonism alone rarely causes low blood sugar. On the alpha cell it suppresses glucagon; in the stomach it slows emptying. The effect that drives weight change, though, is central: GLP-1 receptors in the hypothalamus and the area postrema, a brainstem region outside the blood-brain barrier, reduce hunger. Appetite falls, and the weight follows.
What the research shows for semaglutide
With semaglutide the question is not whether human evidence exists but how to summarise the amount of it. Three randomised, controlled programmes ran in sequence: SUSTAIN for the weekly injection in type 2 diabetes, PIONEER for the oral tablet, and STEP for weight management at 2.4 mg.
The headline weight result comes from STEP 1, published in 2021. Adults with overweight or obesity and without diabetes received 2.4 mg weekly or placebo for 68 weeks alongside lifestyle counselling. Mean body weight fell by 14.9% on semaglutide against 2.4% on placebo. The spread matters as much as the mean: some participants lost more than a fifth of their body weight, others very little.
Beyond weight: the SELECT outcome trial
Weight loss is a surrogate. SELECT, reported in 2023, tested the outcome itself: people with overweight or obesity and established cardiovascular disease but without diabetes, followed for more than three years. It found a 20% relative reduction in major adverse cardiovascular events against placebo, the strongest evidence any peptide in this class holds.
The third strand is pharmaceutical. Peptides are destroyed by stomach acid, so an oral GLP-1 agonist was long thought impractical; Rybelsus co-formulates semaglutide with the absorption enhancer SNAC, which helps the peptide cross the gastric epithelium. Absorption is low and variable, which is why the oral doses are far larger than the injected ones.
Doses used in published research
| Setting | Dose and route | Interval | Duration |
|---|---|---|---|
| STEP 1 (obesity, 2021) | 2.4 mg subcutaneous | Weekly | 68 weeks |
| SELECT (cardiovascular, 2023) | 2.4 mg subcutaneous | Weekly | More than 3 years mean follow-up |
| Wegovy escalation (label) | 0.25 → 0.5 → 1.0 → 1.7 → 2.4 mg | Step up every 4 weeks | 16 weeks to target dose |
| Ozempic (type 2 diabetes, label) | 0.25 mg start, then 0.5, 1.0 or 2.0 mg | Weekly | Maintenance |
| Rybelsus (oral tablet, label) | 3, 7 or 14 mg by mouth | Once daily, fasted | Maintenance |
The stepped escalation is not caution for its own sake: nausea is far more common when the dose rises quickly, and tolerance to it builds over about four weeks while the appetite effect persists.
These figures describe what regulated trials and approved labels used in supervised patients: study designs and prescribing information, recorded for reference, not instructions. Research material sold without a marketing authorisation is for laboratory work only.
Safety and side effects of semaglutide
The safety profile rests on controlled trials and years of post-authorisation pharmacovigilance rather than case reports.
- Gastrointestinal effects. Nausea, vomiting, diarrhoea and constipation are the most frequent findings, strongest during escalation and fading at a stable dose. They were the commonest reason participants discontinued.
- Gallbladder events. Gallstones and cholecystitis appear more often than on placebo, consistent with rapid weight loss and reduced gallbladder motility.
- Pancreatitis. Rare, and not clearly increased in the large outcome trials, but a labelled warning and a reason to stop.
- Thyroid C-cell tumours in rodents. Seen with long-acting GLP-1 agonists in rats and mice; relevance to humans is unproven. Regulators still contraindicate the medicines where medullary thyroid carcinoma or MEN2 runs in the family.
- Low blood sugar. Uncommon with semaglutide alone, since insulin release is glucose-dependent, but the risk rises sharply alongside insulin or a sulfonylurea.
- Retinopathy. More diabetic retinopathy complications in the SUSTAIN-6 trial, attributed largely to the speed of glucose improvement in people with existing eye disease.
Regulatory status of semaglutide in Europe
Semaglutide holds central EU marketing authorisations under three brand names: Ozempic (subcutaneous, type 2 diabetes), Rybelsus (oral, type 2 diabetes) and Wegovy (subcutaneous, weight management). All three are prescription-only, assessed by the European Medicines Agency and dispensed through pharmacies. A vial of semaglutide research material is none of these products: no marketing authorisation, no regulatory assessment, supplied for laboratory use.
That distinction is legal, not cosmetic. In the EU a medicinal product may only be placed on the market with an authorisation, though rules on possession and personal import differ from country to country. Semaglutide is not currently named on the WADA Prohibited List, which is revised each year; competing athletes should check the version in force rather than rely on a profile page.
Sourcing semaglutide and checking quality
King Peptides lists this compound as Sema (Semaglutide) 10 mg, sold as research material. It is not Ozempic, Wegovy or Rybelsus: the molecule being identical to the one in an authorised medicine changes nothing about the status of the vial. What a supplier can be held to is analysis.
Ask for the lot-specific certificate of analysis and read two numbers on it. HPLC purity should be at least 99%, and the mass spectrometry result should land on 4113.6 Da, matching the molecular panel beside this article; a mass out by a few hundred daltons points to a different peptide or a truncated synthesis. Our guide to reading a certificate of analysis explains what the chromatogram and the mass trace show. Lyophilised material ships and is stored at −20 °C, as set out in the storage and reconstitution guide. Orders leave the Netherlands and stay inside the EU: usually 1–2 business days within the Netherlands, 3–5 business days elsewhere in the EU, no customs. Shipments to the United Kingdom, Switzerland or Norway can be subject to import rules and duties. Packaging is neutral and tracked, and at checkout buyers confirm that they order for research and are at least 18.
Frequently asked questions about semaglutide
Is semaglutide research material the same thing as Ozempic or Wegovy? No. The peptide may be identical, but an authorised medicine is a product made under pharmaceutical quality rules, assessed by a regulator and supplied with a patient leaflet. Research material has none of that.
Why is the weight-management dose higher than the diabetes dose? Glucose control improves at lower exposures than appetite suppression does: 0.5 to 2.0 mg weekly against 2.4 mg.
How does semaglutide compare with tirzepatide and retatrutide? It acts on one receptor rather than two or three, and has the longest evidence trail of the three. The numbers sit side by side in our comparison of the three incretin peptides, and the tirzepatide profile covers what the second receptor adds.
Why does a 10 mg vial look nothing like a 2.4 mg trial dose? A vial of lyophilised powder is bulk raw material for laboratory work, not a measured dose. Concentration and the amount used per experiment are set by the study protocol.
Research use only. Semaglutide is described here for laboratory and scientific research. Research material carries no marketing authorisation, whatever the status of the molecule as a medicine elsewhere, and it is not intended for human or veterinary use. Nothing on this page is medical advice, and the dosing information above summarises published study designs. Always comply with the laws that apply in your country.