Quick Comparison
| GLP-1 | Semaglutide | |
|---|---|---|
| Half-Life | 1-2 minutes | 168 hours (7 days) |
| Typical Dosage | Not used therapeutically due to extremely short half-life. Research: continuous intravenous infusion at variable rates. All approved GLP-1 therapies use modified analogues with extended half-lives instead. | Weight management (Wegovy): 0.25 mg subcutaneous once weekly, escalating over 16 weeks to 2.4 mg once weekly. Diabetes (Ozempic): 0.25 mg subcutaneous once weekly, escalating to 1-2 mg once weekly. Oral (Rybelsus): 3 mg once daily for 30 days, then 7-14 mg once daily on an empty stomach. |
| Administration | Subcutaneous injection or intravenous infusion | Subcutaneous injection (weekly). Oral formulation available (Rybelsus). |
| Research Papers | 32 papers | 30 papers |
| Categories |
Mechanism of Action
GLP-1
GLP-1 (glucagon-like peptide 1) is the native incretin hormone produced by enteroendocrine L-cells in the distal small intestine and colon in response to nutrient ingestion. It is the endogenous molecule that all GLP-1 receptor agonist drugs (semaglutide, liraglutide, etc.) are designed to mimic. Understanding native GLP-1 is essential to understanding the entire drug class built upon its biology.
Upon release, GLP-1 binds to GLP-1 receptors (GLP-1R) — G protein-coupled receptors expressed on pancreatic beta cells, the GI tract, the heart, the kidneys, and critically, the brain. In the pancreas, GLP-1R activation stimulates adenylyl cyclase, raising intracellular cAMP levels, which potentiates glucose-stimulated insulin secretion. This glucose-dependence is a key safety feature — GLP-1 only promotes insulin release when blood sugar is elevated, minimizing hypoglycemia risk. Simultaneously, GLP-1 suppresses glucagon secretion from alpha cells, further reducing hepatic glucose output.
In the brain, GLP-1 receptors in the hypothalamus (arcuate nucleus, paraventricular nucleus) and brainstem (area postrema, nucleus tractus solitarius) mediate appetite suppression and satiety. GLP-1 also activates vagal afferents to slow gastric emptying, prolonging nutrient absorption and post-meal satiety. The critical limitation of native GLP-1 is its extremely rapid degradation by the enzyme dipeptidyl peptidase-4 (DPP-4), which cleaves the first two amino acids within 1-2 minutes, rendering it inactive. This ultra-short half-life is why pharmaceutical GLP-1 analogues require structural modifications (albumin binding, DPP-4 resistance) to achieve clinically useful durations of action.
Semaglutide
Semaglutide is a modified version of the natural incretin hormone GLP-1, engineered with 94% structural homology to the native peptide. It binds to GLP-1 receptors expressed throughout the body, triggering a cascade of metabolic effects. In the pancreas, it stimulates glucose-dependent insulin secretion from beta cells while suppressing glucagon release from alpha cells, providing dual glycemic control that only activates when blood sugar is elevated.
In the central nervous system, semaglutide crosses the blood-brain barrier and acts on GLP-1 receptors in the hypothalamic arcuate nucleus and the brainstem's nucleus tractus solitarius. This suppresses appetite by modulating POMC/CART (anorexigenic) and NPY/AgRP (orexigenic) neuronal pathways. The result is a significant reduction in hunger, food cravings, and caloric intake — patients typically experience a fundamental shift in their relationship with food.
The extended duration of action comes from a C18 fatty di-acid chain attached at position 26 (lysine), which enables strong non-covalent binding to circulating albumin. This albumin binding shields semaglutide from DPP-4 enzymatic degradation — the process that destroys native GLP-1 within minutes — extending its half-life to approximately 7 days. Additionally, semaglutide slows gastric emptying through vagal nerve signaling, contributing to post-meal satiety and reduced glycemic excursions.
Risks & Safety
GLP-1
Common
nausea and vomiting at higher doses.
Serious
dangerously low blood sugar if combined with insulin or diabetes medications.
Rare
allergic reactions.
Semaglutide
Common
nausea (30-45% of users), vomiting, diarrhea, constipation, stomach pain, headache.
Serious
inflammation of the pancreas (pancreatitis), gallstones, kidney problems from dehydration, loss of muscle mass alongside fat.
Rare
thyroid tumours seen in animal studies, severe allergic reactions.
Full Profiles
GLP-1 →
The natural appetite hormone that your gut produces after eating — it's what all GLP-1 weight loss drugs (semaglutide, tirzepatide, etc.) are designed to copy. Your body makes it naturally, but it breaks down within 1-2 minutes, which is far too fast to use as a medicine. That's why drug companies created modified versions that last days instead of minutes. Included here because understanding GLP-1 is key to understanding the entire class of modern weight loss drugs.
Semaglutide →
The most widely prescribed weight loss medication in the world, sold as Wegovy and Ozempic. Works by dramatically reducing appetite and food cravings — most people report feeling full much faster and losing interest in snacking. In clinical trials, patients lost an average of 15-17% of their body weight. Also available as a daily pill (Rybelsus). Originally developed for type 2 diabetes, it also helps control blood sugar levels.