What GLP-1 normally does
GLP-1 is an incretin hormone, it’s secreted by L-cells in the small intestine in response to food, and its job is to coordinate the body’s postprandial response. It stimulates insulin release (glucose-dependently), suppresses glucagon, slows gastric emptying, and signals satiety to the brain.
Natural GLP-1 is degraded within minutes by the enzyme DPP-4, which is why the native hormone isn’t useful as a drug. Semaglutide’s design, amino acid substitutions at the DPP-4 cleavage site plus a fatty-acid chain that binds albumin, resists degradation and slows clearance.
Where the GLP-1 receptor lives
GLP-1 receptors are expressed in three places that matter for the clinical effect:
- Pancreatic beta cells. Receptor activation potentiates glucose-stimulated insulin release, insulin goes up only when blood glucose is elevated, which is why GLP-1 agonists carry low hypoglycemia risk on their own.
- Hypothalamic appetite centers. GLP-1 receptors in the arcuate nucleus and other hypothalamic regions mediate the appetite-suppressing effect. Patients often describe the subjective change as quieter food noise and longer satiety after meals.
- Gut smooth muscle. Receptor activation slows gastric emptying, food stays in the stomach longer, which extends the physical sensation of fullness and flattens post-meal glucose curves.
Once-weekly pharmacokinetics
Semaglutide’s half-life is about 165 hours, roughly a week. That ’s the result of two design features. The amino-acid modification at position 8 prevents DPP-4 from cleaving the peptide. The fatty-acid side chain binds reversibly to albumin, which keeps semaglutide in circulation and slows renal clearance.
Steady-state is reached after roughly 4–5 weeks of weekly dosing. Standard protocols titrate upward slowly from a low starting dose to mitigate the GI side effects that are dose- and titration-dependent.
What the contraindications reflect
The MTC / MEN2 contraindication comes from rodent studies showing thyroid C-cell proliferation at high doses. The clinical significance in humans is uncertain, but the label is cautious: patients with personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2 should not be prescribed.
Pancreatitis history warrants caution. Rare cases of pancreatitis have been reported with GLP-1 agonists; clinicians look for prior episodes and any active symptoms before and during therapy.
Pregnancy is an exclusion: GLP-1 agonists are not prescribed during pregnancy or active attempts to conceive. Clinical review covers these as part of the assessment.