What Is Semaglutide? The GLP-1 Peptide Explained

The short version

So, what is semaglutide? It is a man-made copy of a natural gut hormone, built into a medicine. After you eat, your intestine releases a hormone called GLP-1 that tells the body to make insulin, quiets hunger, and slows how fast the stomach empties. Semaglutide is a semaglutide peptide — a small protein-like molecule — that does the same job but lasts about a week instead of a couple of minutes. Because it lasts so long, it can be taken as a once-weekly shot or a daily pill. Doctors prescribe it for type 2 diabetes, long-term weight management, lowering heart risk in some people, and a serious fatty-liver disease called MASH. It is a fully approved medicine, not an experimental research chemical. The plain trade-off: the benefits are real and measured, and so are side effects like nausea, which this digest covers in full.

The drug class: a GLP-1 receptor agonist

Semaglutide belongs to the GLP-1 receptor agonist class (an "agonist" is a molecule that switches a receptor on). The receptor in question is the GLP-1 receptor, the docking point for the body's own incretin hormone GLP-1. By switching that receptor on, semaglutide reproduces the natural hormone's effects: it prompts glucose-dependent insulin secretion (insulin released only when blood sugar is high, which keeps the risk of dangerous lows down), suppresses the counter-regulatory hormone glucagon, slows gastric emptying, and reduces appetite.

The central, mechanistic, and clinical detail behind those effects is documented across the rest of this digest. The molecule's weight-lowering action is primarily central — it reaches brain appetite circuits rather than simply emptying the stomach more slowly — a point covered on how does semaglutide work. Semaglutide was developed by Novo Nordisk on the foundation of the earlier GLP-1 analogue liraglutide ^[6].

The semaglutide peptide: a 31-amino-acid acylated structure

As a peptide, semaglutide is a chain of 31 amino acids — an acylated analogue of human GLP-1 sharing about 94% of its sequence. Its molecular formula is C187H291N45O59 and its molecular weight is 4113.64 Da (CAS 910463-68-2; UNII 53Axs5j8mn; ATC code A10BJ06).

Three engineered changes explain why this peptide outlasts the natural hormone, which is cleared within roughly two minutes. First, an alpha-aminoisobutyric-acid (Aib) substitution at position 8 blocks DPP-4, the enzyme that normally chews up GLP-1. Second, a lysine-to-arginine swap at position 34 prevents acylation in the wrong place. Third, a C18 fatty di-acid side chain attached at the position-26 lysine (via a glutamic-acid/ADO spacer) binds reversibly and strongly to albumin, the most abundant blood protein — which shields the peptide from the kidney and is the structural basis for once-weekly dosing ^[7]. A 2024 systematic review of semaglutide pharmacokinetics confirms a long elimination half-life supporting once-weekly subcutaneous administration ^[8].

Approved indications and formulations

Semaglutide is FDA-approved across multiple indications and two formulations. As a once-weekly subcutaneous injection and a once-daily oral tablet, it is approved for type 2 diabetes mellitus, chronic weight management, reduction of major adverse cardiovascular events in adults with established cardiovascular disease and overweight or obesity, and — added in 2025 — metabolic dysfunction-associated steatohepatitis (MASH) ^[6].

The magnitude behind those indications is documented in the trial record: a mean body-weight change of -14.9% at 68 weeks in STEP 1 ^[2], a 20% reduction in major adverse cardiovascular events in SELECT ^[4], a 24% reduction in major kidney events in FLOW ^[5], and steatohepatitis resolution in 62.9% versus 34.3% in the 2025 ESSENCE MASH trial ^[1]. This site uses only the International Nonproprietary Name, semaglutide, and discusses doses only as they were documented in published trials and labelling — never as advice for an individual.