Detailed Explanation
Semaglutide is a GLP-1 receptor agonist peptide drug marketed as Ozempic (injection for type 2 diabetes), Wegovy (injection for obesity), and Rybelsus (oral tablet for diabetes). It is a modified analog of human GLP-1(7-36) with three key changes: an Aib (α-aminoisobutyric acid) substitution at position 8 for DPP-IV resistance, a Lys34→Arg substitution, and acylation at Lys26 with an octadecanedioic acid (C18 fatty diacid) via a mini-PEG linker.
The C18 fatty diacid acylation is the critical innovation. It enables reversible binding to serum albumin, which shields semaglutide from enzymatic degradation and renal filtration, extending the half-life from ~2 minutes (native GLP-1) to approximately 7 days. This allows once-weekly subcutaneous dosing. Semaglutide activates GLP-1 receptors on pancreatic β-cells to stimulate glucose-dependent insulin secretion, on α-cells to suppress glucagon, on gastric smooth muscle to slow gastric emptying, and on hypothalamic neurons to reduce appetite.
The STEP clinical trial program demonstrated 15–17% body weight loss with weekly semaglutide 2.4 mg, making it the most effective anti-obesity peptide drug. The SELECT cardiovascular outcomes trial showed a 20% reduction in major adverse cardiovascular events independent of diabetes status. Oral semaglutide (Rybelsus) is co-formulated with SNAC (sodium N-[8-(2-hydroxybenzoyl)amino]caprylate), an absorption enhancer, though oral bioavailability remains only ~1%. Semaglutide generated over $18 billion in revenue for Novo Nordisk in 2023.
Key Facts
- Brand names: Ozempic (diabetes), Wegovy (obesity), Rybelsus (oral diabetes)
- Modified GLP-1 analog with Aib8, Arg34, and C18 diacid acylation at Lys26
- Half-life: ~7 days (vs. ~2 minutes for native GLP-1)
- Weight loss: 15–17% in STEP trials
- SELECT trial: 20% reduction in cardiovascular events
- Oral form (Rybelsus) has ~1% bioavailability using SNAC enhancer
- Revenue exceeded $18 billion in 2023
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