Quick Comparison
| Semaglutide | Tirzepatide | |
|---|---|---|
| Half-Life | 168 hours (7 days) | 120 hours (5 days) |
| Typical Dosage | 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. | Weight management (Zepbound): 2.5 mg subcutaneous once weekly for 4 weeks, increasing by 2.5 mg every 4 weeks to maintenance dose of 5-15 mg once weekly. Diabetes (Mounjaro): same escalation schedule, maintenance 5-15 mg subcutaneous once weekly. |
| Administration | Subcutaneous injection (weekly). Oral formulation available (Rybelsus). | Subcutaneous injection (weekly) |
| Research Papers | 30 papers | 30 papers |
| Categories |
Mechanism 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.
Tirzepatide
Tirzepatide is the first approved dual incretin receptor agonist, simultaneously activating both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptors. This dual mechanism represents a paradigm shift in obesity and diabetes treatment because the two receptor systems produce complementary and additive metabolic effects that neither achieves alone.
The GLP-1 receptor component works similarly to semaglutide — suppressing appetite through hypothalamic signaling, slowing gastric emptying, and stimulating glucose-dependent insulin secretion. However, the addition of GIP receptor agonism provides unique benefits. GIP receptors in adipose tissue enhance lipid metabolism and may improve fat storage efficiency, while GIP signaling in the brain appears to amplify the appetite-suppressing effects of GLP-1 through distinct neuronal circuits in the hypothalamus.
At the pancreatic level, the dual stimulation of both GIP and GLP-1 receptors on beta cells produces a more robust insulin secretory response than either pathway alone. Tirzepatide also improves insulin sensitivity in peripheral tissues, reduces hepatic fat content, and lowers triglyceride levels. The molecule is built on a modified GIP peptide backbone with GLP-1 receptor cross-reactivity, attached to a C20 fatty di-acid moiety that enables albumin binding and weekly dosing. Clinical trials have shown weight loss of up to 22.5% of body weight, surpassing GLP-1-only agents.
Risks & Safety
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.
Tirzepatide
Common
nausea (25-35%), diarrhea, constipation, vomiting, reduced appetite, stomach pain, redness at injection site.
Serious
inflammation of the pancreas (pancreatitis), gallstones, very slow stomach emptying (gastroparesis), low blood sugar if combined with other diabetes medications.
Rare
thyroid tumours seen in animal studies, severe allergic reactions, kidney problems.
Full Profiles
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.
Tirzepatide →
Sold as Mounjaro and Zepbound, this is one of the most effective weight loss medications available. It works by targeting two appetite hormones at once (GIP and GLP-1), making it more powerful than medications like semaglutide that only target one. People in clinical trials lost up to 22.5% of their body weight. Also FDA-approved for type 2 diabetes, and improves cholesterol and blood fat levels.