Semaglutide: What the Evidence Shows and What It Does Not
Semaglutide is a GLP-1 receptor agonist, supplied in Australia as a research material and studied for body weight and glucose regulation. It acts at one receptor rather than two or three. This guide sets out what the published trials measured, which findings are human and which are rodent, what happened when treatment was withdrawn, the adverse effects those trials reported, and what remains unestablished about material sold for laboratory use. For in vitro research purposes only.
8 minute read
What Is Semaglutide?
Semaglutide is a re-engineered copy of GLP-1, a hormone released by cells in the gut. Three structural changes separate the copy from the original, and the paper that describes them gives a single reason for all three: to produce an analogue that could be given once a week.
Glucagon-like peptide-1 is what the abbreviation stands for. Drucker describes the natural hormone as released from gut enteroendocrine cells, augmenting insulin secretion, inhibiting glucagon secretion, and slowing both gastric emptying and food intake. Those are properties of the hormone. What a modified copy of it does is a separate question, answered by the trials further down.
| Change | Where it sits | What the discovery paper reports |
|---|---|---|
| Aib substitution | Amino acid 8 | One of two amino acid substitutions distinguishing the molecule from human GLP-1 |
| Arginine substitution | Amino acid 34 | The second of the two substitutions |
| A fatty acid, joined through a linker | Lysine 26 | Named as the key feature securing high albumin affinity, receptor potency and prolonged exposure |
How Does Semaglutide Work?
Semaglutide works by switching on a single receptor, the GLP-1 receptor, and it reaches nothing else. Compounds that switch a receptor on are called agonists, and semaglutide is an agonist at one of them — which is the shortest way to place it beside the dual and triple agonists in the same catalogue category.
The measured strength of that binding is 0.38 nanomolar. The same paper reports it as three-fold weaker than liraglutide’s, while the molecule’s affinity for albumin — the carrier protein it rides on in the blood — went the other way and increased. The receptor targets guide covers what the GLP-1 receptor is and how it differs from the other two in this family.
Why Is Semaglutide Given Once a Week?
Because it was designed to be. The stated aim of the work that produced semaglutide was a once-weekly analogue, reached by raising affinity for albumin and securing full stability against metabolic degradation, and every trial on this page used a once-weekly interval.
The animal figures behind that design are specific and worth reading as what they are. Plasma half-life measured 46.1 hours in mini-pigs given the peptide into a vein, with a mean residence time of 63.6 hours after an injection under the skin in the same species. Those are mini-pig numbers by two different routes, not human ones.
What Do the Published Trials Show?
Four large trials carry most of the published human record, and each studied a different population for a different reason. The table sets out who was enrolled and what each trial reported, because a percentage detached from its population is not a finding.
| Trial | Who was studied, and for how long | What was reported |
|---|---|---|
| STEP 1 | 1,961 adults with overweight or obesity and without diabetes, treated weekly for 68 weeks alongside lifestyle intervention | Mean body-weight change of −14.9% against −2.4% on placebo. Around 86% reached a reduction of at least 5%, against 32% on placebo |
| STEP 2 | 1,210 adults who had type 2 diabetes as well as overweight or obesity, randomised across three treatment arms and followed for 68 weeks | Estimated mean body-weight change of −9.6% against −3.4% on placebo |
| STEP 5 | 304 adults with overweight or obesity, followed for 104 weeks — the longest of the four trials here | −15.2% against −2.6% on placebo, with about 77% reaching at least 5% against 34%. Gastrointestinal adverse events were reported in 82.2% against 53.9% |
| SELECT | 17,604 adults with established cardiovascular disease and overweight or obesity, but without diabetes | A primary cardiovascular endpoint event in 569 of 8,803 people (6.5%) against 701 of 8,801 (8.0%) on placebo |
Read those rows as four separate experiments rather than as one escalating story. STEP 2 enrolled people with diabetes and STEP 1 did not, which is why their percentages differ; SELECT was measuring cardiovascular events rather than weight at all. Nothing in the table is a projection for anybody outside the group described beside it.
What Did the Animal Studies Measure?
The rodent work answered a mechanism question the human trials could not: where in the body the effect is initiated. Gabery and colleagues reported that semaglutide did not cross the blood-brain barrier, reaching brain tissue instead through the circumventricular organs and several sites next to the ventricles.
In the same study the peptide modulated food preference, reduced food intake and lowered body weight without decreasing energy expenditure. It produced c-Fos activity in ten brain areas, including regions it never touched directly. In rats, tissue from the area postrema showed increased prolactin-releasing hormone and tyrosine hydroxylase.
Every one of those is a measurement in mice or rats. Animal findings establish how something might work; they do not establish what happens in a person, and this page keeps the two apart on purpose.
What Happens When Semaglutide Is Stopped?
Most of the lost weight came back. A subset of 327 STEP 1 participants was followed for a further year with no treatment and no lifestyle programme, and by week 120 the semaglutide group had regained 11.6 of the 17.3 percentage points it had lost — roughly two-thirds.
The placebo group in the same extension regained 1.9 percentage points of a 2.0% loss. Net change from the very beginning to week 120 was −5.6% on semaglutide and −0.1% on placebo, and the cardiometabolic measures that had improved by week 68 drifted back toward where they started.
What Side Effects Did the Trials Report?
Gastrointestinal effects dominated in every trial that reported them. Nausea and diarrhoea were named as the most common adverse events in STEP 1, and STEP 5 recorded gastrointestinal adverse events in 82.2% of the semaglutide group against 53.9% on placebo, describing them as mostly mild to moderate.
Discontinuation is the other number worth reading. In SELECT, adverse events led 1,461 of 8,803 people (16.6%) to stop the trial product permanently, against 718 of 8,801 (8.2%) on placebo — a gap of roughly eight percentage points in a trial of more than seventeen thousand participants.
All of those figures describe a registered pharmaceutical given under a protocol, with supervision, dose escalation and monitoring built in. No published study reports what laboratory-grade powder does in a person, because no such study has been run.
How Pure Is Unregulated Semaglutide?
One published study has actually measured it, and the answer was poor. Ashraf and colleagues analysed 1,080 search engine links, identified 317 pharmacy websites of which 134 were illegal, and made test purchases from six of them. Three vials arrived, and all three were judged probable substandard or falsified products.
- Content exceeded the label by between 28.56% and 38.69%.
- Purity measured between 7.7% and 14.37%, against a claimed 99%.
- Endotoxin contamination appeared in every sample.
That is a finding about those sellers rather than about any other, and it is quoted here because a measurement is a rarer thing in this market than an assertion. What it demonstrates is narrower and more useful than a warning: a purity claim printed on a listing is not evidence, and the only thing that answers the question is a laboratory report tied to the batch in the vial. Testing, purity and certificates of analysis sets out what each analysis measures and how a certificate reports it.
What Is Not Established?
A large evidence base is not a complete one, and the gaps here are specific rather than general.
- No trial used research-grade material. Every figure above came from a manufactured pharmaceutical supplied under a trial protocol. Laboratory powder has never been the subject of a published clinical study.
- The longest weight trial cited here ran 104 weeks. Anything asserted about a decade is not coming from these papers.
- Off-treatment follow-up covers one year in 327 people drawn from an original 1,961 — a subset, analysed as exploratory by its own authors.
- The animal and human records answer different questions. Neither substitutes for the other, and a rodent mechanism does not become a human outcome by being quoted next to one.
- No published head-to-head against a triple agonist exists. Retatrutide versus semaglutide sets out why comparing percentages across separate trials cannot rank two compounds.
Is Semaglutide Approved in Australia?
Approval attaches to a finished medicine, not to a molecule. Registered semaglutide medicines exist in Australia and are prescription items, assessed as complete products with a manufacturer, a strength and a label standing behind each one.
The vial sold on this site is none of those things. It is unregistered material supplied for in vitro laboratory research, and sharing a chemical name with an approved product transfers no part of that product’s assessment to it. In vitro research requirements sets out what a purchaser of research material is taking on.
How Is Semaglutide Supplied for Research?
As a freeze-dried solid in a sealed glass vial, in a single 10 mg strength, from the semaglutide listing. Every batch is HPLC tested before release. The certificate covering the strength ARP holds reports a purity of 99.262%, and the document itself is published in the certificate library rather than summarised.
The powder has to be dissolved before any assay, and the volume chosen is what fixes the concentration. The reconstitution calculator guide works through that arithmetic, and storage and handling covers what the dry material tolerates before it is opened.
Common Questions
No. A registered medicine is a finished product that a regulator has assessed, with a named manufacturer answerable for each batch. The material listed here is unregistered powder supplied for laboratory research. The molecule is shared; the assessment, the supply route and the permitted purpose are not.
One. Semaglutide is an agonist at the GLP-1 receptor and reaches no others, which is what separates it from the dual and triple agonists listed in the same category. Acting on fewer receptors is a difference in design rather than a mark of quality.
Not in rodents. Gabery and colleagues reported that it failed to cross the blood-brain barrier and reached brain tissue instead through the circumventricular organs and a few sites beside the ventricles, while still producing activity in ten brain areas. That is a rodent finding and is stated as one.
Not for body weight in a published trial. STEP 5 followed 304 adults for 104 weeks and is the longest of the trials cited here. SELECT ran in a much larger group but was measuring cardiovascular events, which is a different endpoint answering a different question.
Because a listing can claim any purity it likes and a laboratory report cannot. The one published analysis of semaglutide bought from illegal online sellers found purity between 7.7% and 14.37% against a claimed 99%, with endotoxin in every sample. A batch document is what turns a claim into something checkable.
Australian Research Peptides catalogues semaglutide as one 10 mg vial of freeze-dried powder, held in local stock and covered by a laboratory certificate published in full, dispatched inside Australia for bench work and never as the medicine whose trials are described above.
References
- 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 (PMID 26308095)
- Drucker DJ. Mechanisms of Action and Therapeutic Application of Glucagon-like Peptide-1. Cell Metabolism 2018;27(4):740-756 (PMID 29617641)
- Gabery S, Salinas CG, Paulsen SJ, et al. Semaglutide lowers body weight in rodents via distributed neural pathways. JCI Insight 2020;5(6):e133429 (PMID 32213703)
- 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 (PMID 33567185)
- Davies M, Færch L, Jeppesen OK, et al. Semaglutide 2.4 mg once a week in adults with overweight or obesity, and type 2 diabetes (STEP 2). The Lancet 2021;397(10278):971-984 (PMID 33667417)
- Garvey WT, Batterham RL, Bhatta M, et al. Two-year effects of semaglutide in adults with overweight or obesity: the STEP 5 trial. Nature Medicine 2022;28:2083-2091 (PMID 36216945)
- Wilding JPH, Batterham RL, Davies M, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes, Obesity and Metabolism 2022;24(8):1553-1564 (PMID 35441470)
- 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 (PMID 37952131)
- Ashraf AR, Mackey TK, Vida RG, et al. Multifactor Quality and Safety Analysis of Semaglutide Products Sold by Online Sellers Without a Prescription. Journal of Medical Internet Research 2024;26:e65440 (PMID 39509151)
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