Yes. Semaglutide is a synthetic peptide: a 31-amino-acid analogue of human glucagon-like peptide-1, with a molecular weight of 4113.58 g/mol and the formula C187H291N45O59. The FDA label states it shares 94% sequence homology with native human GLP-1.
It is not an insulin, not a small molecule, and not a protein in the conventional sense — at roughly 4.1 kilodaltons it sits squarely in peptide territory.
The three modifications that matter
Native GLP-1 has a half-life of minutes. Semaglutide has one of about a week. Three deliberate changes to the molecule account for that gap.
- Position 8: alanine replaced with Aib. The label says this modification provides stabilisation against degradation by the enzyme DPP-4, which is what destroys natural GLP-1 almost immediately.
- Position 34: lysine replaced with arginine. The label describes this as a minor modification to ensure the attachment of only one fatty di-acid — it removes a competing attachment site so the next change lands in exactly one place.
- Position 26: a C18 fatty di-acid on a hydrophilic spacer. This is the one that does the work. The fatty chain binds serum albumin, so the molecule circulates bound rather than being cleared, giving the roughly one-week half-life that makes weekly dosing possible.
The peptide backbone is produced by yeast fermentation and then chemically modified.
Where the line between peptide and protein sits
There is no standards body that fixes it. The convention puts the boundary somewhere around 50 amino acids, or a few kilodaltons, and like most conventions it has exceptions on both sides — insulin at 51 residues is routinely called both. What the convention is really tracking is behaviour: below the line, molecules are made by chemical synthesis or short recombinant routes, are digested if swallowed, and are handled as solutions or lyophilised powders. Semaglutide does all three.
Against the other compounds on this site, it sits in the middle of the range:
- GHK-Cu — 402.92 Da
- Ipamorelin — 711.9 Da
- PT-141 — 1,025.2 Da
- BPC-157 — 1,419.5 Da
- Liraglutide — 3,751.2 Da
- Semaglutide — 31 amino acids, 4,113.58 Da
- Tirzepatide — 39 amino acids, 4,813.53 Da
- IGF-1 LR3 — 9,111 Da
- HGH (somatropin) — 191 amino acids, 22,125 Da
Somatropin is the outlier and it is instructive: at 191 amino acids and about 22 kilodaltons it is a protein by any convention, and it behaves like one — produced recombinantly, supplied in cartridges with their own diluent, and far more particular about handling than the small synthetic peptides above it.
Being a peptide is why you cannot simply swallow it
This is the practical consequence of everything above. A peptide taken by mouth meets the same proteolytic machinery that digests dietary protein, which is why the injectable presentations exist at all.
The oral product is the exception that proves it. Semaglutide tablets are co-formulated with salcaprozate sodium — SNAC — listed among the inactive ingredients as an absorption enhancer, and the label states that absorption predominantly occurs in the stomach. The formulation had to be designed around the molecule’s peptide nature rather than in spite of it. That is also why the tablet doses and the injection doses are not comparable numbers: they are solving different absorption problems.
Then is Ozempic a peptide?
Ozempic is a brand of semaglutide, so yes — same molecule. Novo Nordisk markets semaglutide under several names for different indications: Ozempic for type 2 diabetes, Wegovy for weight management, cardiovascular risk reduction and MASH, and Rybelsus as a tablet. The approved doses differ by brand; Ozempic tops out at 2 mg weekly, Wegovy at 7.2 mg.
Liraglutide is the same family with a shorter chain — a C16 palmitic acid instead of the C18 di-acid — which binds albumin less tightly and leaves a 13-hour half-life. That is why Victoza and Saxenda are daily injections and Ozempic is weekly. Liraglutide details.
Why compounded semaglutide is a powder when the real thing is not
This confuses a lot of people arriving at a reconstitution calculator. Every FDA-approved semaglutide injection is a ready-to-use sterile aqueous solution in a pen or prefilled syringe. The label describes it exactly that way. There is no approved lyophilised semaglutide powder, and reconstitution is not part of any approved label.
Powder vials come from compounders and grey-market suppliers. The FDA has been explicit about the risks there: compounded drugs are not FDA approved and are not reviewed for safety, effectiveness or quality before marketing, and the agency has received multiple reports of adverse events, some requiring hospitalisation, that may be related to dosing errors with compounded injectable semaglutide. It has also flagged that salt forms such as semaglutide sodium or acetate are not the same active ingredient as the approved drug.
The shortage that originally justified compounding it was declared resolved on 21 February 2025.
How long it stays in your system
The Wegovy label states semaglutide remains in circulation for about 5 to 7 weeks after the last 2.4 mg or 7.2 mg injection, on a half-life of roughly one week. Steady state arrives after 4 to 5 weeks of weekly dosing — which is also why titration steps are spaced 4 weeks apart rather than weekly. Half-lives and clearance for every GLP-1, and how long semaglutide takes to work.
Full semaglutide details, titration schedule and calculator.