THE MOLECULE / WHAT IT IS
What is semaglutide? A copy of a gut hormone, rebuilt to last.
A 31-amino-acid GLP-1 analogue, engineered so a two-minute signal could become a once-weekly medicine.
In plain English
So, what is semaglutide? It is a peptide — a short chain of amino acids, the same building blocks that make up the proteins in your body. Specifically, it is a man-made copy of a natural gut hormone called GLP-1 (glucagon-like peptide-1), the signal your gut sends after a meal that helps you feel full and helps your body manage blood sugar.
The trouble with the natural hormone is that it disappears in about two minutes. Semaglutide is the same idea, redesigned so it survives for about a week. Scientists changed a couple of points in the chain and bolted on a fatty-acid tail that lets it hitch a ride on a blood protein, so the body clears it slowly [9].
That is the whole trick: take a fleeting natural signal and make it last, so it can be given as a once-weekly injection or a daily tablet. It is an approved medicine, not an experiment.
Semaglutide peptide: the structure
As a peptide, semaglutide is a 31-amino-acid acylated analogue of human GLP-1, sharing about 94% of its sequence with the natural hormone. Two changes to the backbone give it staying power: at position 8, the amino acid alanine is swapped for a non-standard one (alpha-aminoisobutyric acid, or Aib) that blocks the enzyme DPP-4 from cutting the peptide apart, and at position 34 lysine is replaced by arginine. The single remaining lysine, at position 26, carries a C18 fatty di-acid side chain attached through a short spacer [9].
That fatty tail is the heart of the design. It binds strongly but reversibly to serum albumin — the most abundant protein in blood — which shields the peptide from the kidney's filters and from metabolism, and is the structural reason once-weekly dosing is possible [9]. Its molecular formula is C187H291N45O59 and its molecular weight is about 4,113.64 daltons.
Where it came from
Semaglutide is the product of a deliberate lineage. It was developed by Novo Nordisk on the foundation of the company's earlier GLP-1 analogue, liraglutide, and engineered specifically for once-weekly dosing through DPP-4 resistance and albumin-binding fatty-acid acylation [23]. It first reached FDA approval for type 2 diabetes in 2017, with an oral once-daily formulation following in 2019-2020 and a chronic weight-management indication in 2021 [23].
The outcomes evidence came later and widened the picture: cardiovascular results (SELECT) in 2023 [3], kidney results (FLOW) in 2024 [6], and the liver result (ESSENCE) supporting a 2025 MASH indication [8]. The pivotal trials anchoring these milestones include STEP 1 for weight, SUSTAIN-6 and SELECT for the heart, FLOW for the kidney, and ESSENCE for the liver [1][2][3][6][8].
What it is used for
Semaglutide is approved across several indications and two formulations — a once-weekly subcutaneous injection and a once-daily oral tablet. The approved uses are type 2 diabetes mellitus, chronic weight management, reduction of major adverse cardiovascular events in adults with established cardiovascular disease and overweight or obesity, and (since 2025) metabolic dysfunction-associated steatohepatitis, or MASH [23].
The through-line across all of these is the gut-hormone signal it imitates. To follow that signal from the bloodstream into the appetite circuits of the brain — and to understand why the same molecule helps with sugar, weight, heart, kidney, and liver — read how does semaglutide work. To see the trials behind each indication, read the Semaglutide research.