What is semaglutide?

Semaglutide is a lipidated peptide agonist of the glucagon-like peptide-1 (GLP-1) receptor, designed by Novo Nordisk from the sequence of human GLP-1. Its 2015 discovery paper states the aim plainly: a once-weekly GLP-1 analogue with higher albumin affinity and full stability against metabolic degradation. ^[1] Reviews place it in the incretin-based class called GLP-1 receptor agonists. ^[9]

GLP-1 is a hormone the gut releases after a meal. The natural hormone lasts minutes in the blood. Semaglutide keeps the parts of GLP-1 that bind its receptor and changes the parts that get it cleared.

Two forms exist in the literature. The once-weekly form is the one studied in SUSTAIN, STEP and SELECT. A once-daily tablet form, co-formulated with an absorption agent called SNAC, was studied in the PIONEER and SOUL trials. ^[10][11][12] Both contain the same peptide. Research-grade semaglutide in a 10mg vial is in stock with a batch certificate.

Semaglutide binds and activates the GLP-1 receptor, a G protein-coupled receptor found in the pancreas, gastrointestinal tract, heart, lungs, kidneys and brain. A 2019 review by Novo Nordisk scientists links the pancreatic receptors to the glucose effects and the brain receptors to the body weight effects seen in studies. ^[9] In Novo Nordisk's assays it bound the receptor with an affinity of 0.38 nM, three-fold weaker than liraglutide, while its albumin affinity increased. ^[1]

The literature describes three layers to the mechanism.

• Pancreas. The same review describes GLP-1 receptor activity in the pancreas as glucose-dependent insulin release, which is why the early trials measured HbA1c in type 2 diabetes. ^[9]
• Brain. In rats and mice, semaglutide reached the brainstem, septal nucleus and hypothalamus through areas next to the ventricles, but did not cross the blood-brain barrier. It activated 10 brain areas and reduced food intake without lowering energy expenditure. ^[13]
• Energy intake in people. The 2019 review cites a 12-week study in people with obesity that reported a 24% average reduction in energy intake over three meals and snacks. ^[9]

The animal work is rodent data, and the review authors work for the developer. Both points matter when you read the mechanism as described.

Semaglutide is a 31-residue linear peptide with one non-coded amino acid, one substituted residue and a fatty acid side chain. Human GLP-1(7-37) supplies the backbone. ^[9] Aib replaces alanine at GLP-1 position 8, arginine replaces lysine at position 34, and the lysine at position 26 carries the fatty acid. ^[1] PubChem's systematic name gives the side chain as a C18 diacid linked through a gamma-glutamic acid and two AEEA spacer units. ^[3]

We checked each value against PubChem on 29 September 2026 and decoded the one-letter sequence from the systematic name, where Aib appears as 2-methylalanyl. ^[3]

Numbering trips up almost everyone who reads the papers. Semaglutide literature uses GLP-1 numbering, which starts at residue 7. So Aib8, Lys26 and Arg34 in the papers are positions 2, 20 and 28 of the 31-residue chain in the table. Two substitutions out of 31 positions means 29 residues match human GLP-1(7-37). ^[1][9]

Each change solves one problem. Aib at position 8 resists cleavage by the enzyme DPP-IV, which breaks down native GLP-1. Native GLP-1 has a half-life of 1.5 minutes after intravenous delivery in humans. ^[9] The C18 diacid binds albumin reversibly, ^[3][9] and SUSTAIN-6 describes semaglutide's half-life as approximately 1 week. ^[4] In mini-pigs, the discovery paper reported a plasma half-life of 46.1 hours after intravenous delivery. ^[1] A crystal structure of the unacylated backbone bound to the receptor matched native GLP-1(7-37). ^[9]

Semaglutide has been examined in randomised human trials in type 2 diabetes, obesity, cardiovascular disease, kidney disease, heart failure, liver disease and Alzheimer's disease, after cell, rodent and mini-pig work. PubMed returned 5,759 records for semaglutide on 29 September 2026. ^[14] The table lists the primary trials behind each area, with the population and what each reported.

Every one of those findings describes a trial population, the developer's pharmaceutical product and trial conditions. None describes a research vial.

The programme ran in a clear order. Novo Nordisk first had to show cardiovascular safety in type 2 diabetes (SUSTAIN-6 and PIONEER 6 were designed to rule out excess risk). Obesity trials followed, then trials asking whether the molecule changed hard outcomes: cardiovascular events in people without diabetes, kidney failure, heart failure symptoms and liver histology. ^[4][11] The brain question came last, and it came back negative.

The semaglutide evidence is broad and deep on clinical endpoints, and it has clear limits a careful reader should hold onto.

1. One sponsor. Novo Nordisk funded SUSTAIN-6, PIONEER 6, STEP 1, SELECT, FLOW, ESSENCE, SOUL and evoke. ^{[4][11][16][18][20][21][12][5]} Its scientists also wrote the discovery paper and the main mechanism review. ^[1][9]
2. A negative brain result. Observational and animal data had pointed to lower dementia risk with GLP-1 receptor agonists. When evoke and evoke+ randomised 3,808 people with early Alzheimer's disease, the tablet form did not slow clinical progression. ^[5] Signals from observational data did not survive the randomised test.
3. Interim and composite results. ESSENCE reports a planned interim analysis at week 72 of a 240-week trial. ^[21] FLOW stopped early after an interim analysis. ^[20] In SUSTAIN-6, nonfatal stroke was the only component with a significant difference (hazard ratio 0.61), and rates of cardiovascular death were similar between groups. ^[4]
4. Uncertain rare events. A 2021 review concluded that definitive conclusions on pancreatic and thyroid cancer cannot be drawn because these conditions are rare. ^[22]
5. No trial used research-grade material. Purity, identity and peptide content of a research vial are a separate question, which is what a batch certificate answers.

Gastrointestinal events were the most common adverse events in every semaglutide trial reviewed here, mostly mild to moderate. A pooled analysis of 16 phase 3a trials with 11,159 participants reported gastrointestinal disorders in 41.9% of participants on the once-weekly form and 39.1% on the tablet form, against 22.0% and 24.8% with comparators. ^[6]

The individual trials reported these events:

• SUSTAIN 1 (388 adults with type 2 diabetes): nausea in 20% and 24% of the two semaglutide groups against 8% on placebo, and diarrhoea in 13% and 11% against 2%. ^[15]
• STEP 1 (1,961 adults with overweight or obesity): nausea and diarrhoea were the most common events, typically transient. Gastrointestinal events led to discontinuation in 4.5% against 0.8% on placebo. ^[16]
• STEP 5 (104 weeks): gastrointestinal adverse events in 82.2% against 53.9% on placebo. ^[17]
• SELECT (17,604 adults): adverse events led to permanent discontinuation in 16.6% against 8.2% on placebo. ^[18]
• SUSTAIN-6 (type 2 diabetes): retinopathy complications were more frequent than with placebo (hazard ratio 1.76). Fewer serious adverse events occurred with semaglutide. ^[4]
• Gallbladder: the pooled SUSTAIN and PIONEER analysis reported higher cholelithiasis (gallstone) incidence than placebo for both forms, with rates of acute pancreatitis and malignant neoplasms similar to comparators. ^[6]
• Eye (observational): a 2025 study across 14 databases covering 37.1 million people with type 2 diabetes reported a modest increase in the risk of nonarteritic anterior ischaemic optic neuropathy, with an incidence rate ratio of 1.32. ^[23]
• Animal data: semaglutide caused thyroid tumours in rats, and it is not known whether this happens in humans. ^[7] Rat thyroid C-cells carry many GLP-1 receptors, while non-human primate and human C-cells show little detectable expression. ^[9]

Serious adverse events were reported less often with semaglutide than placebo in STEP-HFpEF (13.3% against 26.7%) and FLOW (49.6% against 53.8%). ^[19][20] These are trial observations in specific populations, reported as the published record.

Semaglutide is listed in Schedule 4 of the Poisons Standard (prescription only). The entry sits in the June 2026 instrument (F2026L00633), which commenced on 1 June 2026, and the index lists semaglutide under Schedule 4 with no appendix reference. ^[2]

Approval belongs to specific registered products. The TGA names GLP-1 receptor agonists such as semaglutide among the approved peptide-based medicines on the Australian Register of Therapeutic Goods. ^[24] The same TGA page states that "research use only" or "not for human use" disclaimers do not change whether a product is regulated as a therapeutic good. ^[24] Our guide to peptide scheduling and the law in Australia explains what each schedule and the TGA position mean.

For sport, semaglutide is not named on the WADA 2026 Prohibited List, which took effect on 1 January 2026. ^[8] Class S0 covers substances with no current approval by any government health authority for human therapeutic use, and semaglutide holds such approval in Australia. ^[24] WADA revises the List every year, so check the current edition.

Semaglutide targets one receptor, GLP-1. Tirzepatide targets two (GIP and GLP-1) and retatrutide three (GIP, GLP-1 and glucagon). All three are lipidated peptides built for a long half-life and semaglutide is the shortest of them.

The semaglutide column comes from the sources above. ^[3][2] The other columns come from the same PubChem, Poisons Standard and WADA checks we ran for each compound on 29 September 2026. Three randomised trials compared semaglutide with tirzepatide directly, all funded by tirzepatide's developer; the full breakdown, including the sequence overlap, is in semaglutide vs tirzepatide. All three compounds sit in our metabolic research peptides range.

Semaglutide's only published storage conditions describe the manufacturer's solution: refrigerated at 2 to 8°C, kept away from light and heat, and not frozen. ^[7] No published stability study covers lyophilised research material.

For lyophilised vials, keep them sealed, cold, dry and dark until use. For a reconstituted solution, the manufacturer data is the reference point: cold, dark and unfrozen. Our peptide storage guide covers temperatures, light, freeze-thaw and labelling for both states.

On solvents, the primary-source detail comes from Eli Lilly's 2018 methods, where semaglutide was synthesised with traditional peptide chemistry and dissolved in phosphate-buffered saline for preclinical assays. ^[25] We stock BAC Water (sterile water with 0.9% benzyl alcohol) for laboratory reconstitution, and the peptide reconstitution guide explains how to calculate and record the mg per mL concentration.

Peptides Collective sells semaglutide for laboratory research use only, in 10mg vials at A$88. Stock ships as lyophilised powder from Western Australia with tracking.

An independent lab tests every batch before it goes on sale. The certificate reports purity by HPLC and identity by mass spectrometry, and it is published under the batch number printed on the vial. Search the certificate of analysis library by that number and match the report to the vial in your hand.

That check matters for this compound in particular. A 2024 study bought semaglutide vials from online sellers operating without a prescription and analysed them by liquid chromatography and mass spectrometry. Measured purity ranged from 7.7% to 14.37% against 99% claimed on the labels, and endotoxin was detected in every sample. ^[26] The certificate turns a label claim into a measurement you can check against the vial.

Read the certificate against the structure table above: the identity result should correspond to a peptide of about 4114 g/mol. ^[3] Our guide on how to read a peptide certificate of analysis explains the HPLC trace, the mass spectrum and net peptide content, and the semaglutide product page links the certificate for the current batch.

Semaglutide is a 31-amino-acid GLP-1 analogue with two substitutions and an albumin-binding C18 diacid, and its half-life of about a week comes from that design. Its human record spans diabetes, obesity, cardiovascular, kidney, heart failure and liver trials, is almost entirely developer-funded, and includes a clear negative result in Alzheimer's disease. In Australia it is a Schedule 4 substance, and WADA's 2026 List does not name it. For a research vial, the batch certificate is the evidence that settles what is inside.