GLP-1 (7-37) vs Tirzepatide

Binds GLP-1 receptors in the pancreas, gut, and brain. Stimulates glucose-dependent insulin secretion and suppresses glucagon. Central GLP-1 receptor activation reduces food intake via hypothalamic pathways.

GLP-1(7-37) is the native 30-amino-acid active form of glucagon-like peptide 1, an endogenous incretin hormone secreted by intestinal L-cells in response to nutrient ingestion, that acts at GLP-1 receptors throughout the body to stimulate glucose-dependent insulin secretion, suppress glucagon release, slow gastric emptying, reduce appetite, and protect beta-cell mass; it is the endogenous ligand underlying the pharmacology of the GLP-1 receptor agonist drug class. The GLP-1 receptor is expressed on pancreatic beta cells, hypothalamic appetite-regulating neurons, gastric enteric neurons, and cardiovascular tissue; GLP-1(7-37) activates cAMP/PKA signaling in beta cells to potentiate insulin release strictly during hyperglycemia, providing intrinsic hypoglycemia protection, and centrally reduces caloric intake through satiety signaling. A randomized controlled trial of continuous subcutaneous native GLP-1 infusion in patients with type 2 diabetes demonstrated significant reductions in plasma glucose and appetite, confirming receptor-mediated effects of the native peptide in humans; the peptide's very short plasma half-life of approximately 2 minutes due to rapid DPP-IV degradation makes continuous infusion the only practical administration route for the native form. Native GLP-1(7-37) has no FDA approval as a drug; FDA-approved GLP-1 receptor agonists — including semaglutide, liraglutide, dulaglutide, and tirzepatide — are chemically modified DPP-IV-resistant analogs developed to overcome the native peptide's pharmacokinetic limitations, and research-grade native GLP-1 is used exclusively as a tool compound in metabolic pharmacology studies.

Tirzepatide is a dual agonist of both GLP-1 and GIP (glucose-dependent insulinotropic polypeptide) receptors. GIP receptor activation adds a complementary mechanism to GLP-1 agonism — enhancing insulin secretion, reducing glucagon, and modulating adipose tissue metabolism independently of GLP-1 pathways. The combination produces greater average weight reduction in clinical trials than selective GLP-1 agonists at comparable doses.

Tirzepatide is a once-weekly injectable dual agonist of GLP-1 and GIP receptors, FDA approved for type 2 diabetes (Mounjaro) and weight management (Zepbound). Clinical trials demonstrate weight reductions exceeding those seen with semaglutide in head-to-head comparisons. Compounded formulations are offered by telehealth and functional medicine providers across the US. It represents the current clinical benchmark for pharmacological weight management. Mechanism of action: Tirzepatide activates two incretin receptors simultaneously — the glucagon-like peptide-1 (GLP-1) receptor and the glucose-dependent insulinotropic polypeptide (GIP) receptor. GLP-1 activation suppresses appetite, slows gastric emptying, and potentiates insulin secretion; GIP activation independently stimulates insulin release and may reduce some of the GI side effects associated with pure GLP-1 agonism. The dual mechanism produces greater appetite suppression and metabolic improvement than either receptor pathway alone, which accounts for the superior weight reduction seen in clinical trials relative to semaglutide. Clinical evidence: The SURMOUNT trial program established tirzepatide's weight reduction profile. SURMOUNT-1 (2022) found a mean weight reduction of 22.5% over 72 weeks at the highest dose (15mg/week) vs 2.4% with placebo — the largest mean weight reduction reported for any approved pharmacological intervention at that time. SURMOUNT-5 (2024) was a direct head-to-head comparison with semaglutide 2.4mg: tirzepatide 10mg and 15mg produced significantly greater weight reductions (20.2% vs 13.7% for semaglutide). The SURPASS trials established cardiometabolic and glycaemic benefits in T2D contexts. Tirzepatide vs semaglutide: Tirzepatide's dual GIP+GLP-1 mechanism produces greater mean weight reductions in trials but also a distinct side effect profile. GI tolerability may be slightly better than pure GLP-1 agonism for some users due to the GIP component, though nausea and gastrointestinal symptoms remain the most common adverse effects. Semaglutide has a larger body of long-term safety data; tirzepatide has superior head-to-head efficacy data. Prescribers select between them based on clinical context, cost, access, and patient response history. Access and regulatory status: Tirzepatide requires a prescription from a licensed provider. Branded formulations (Mounjaro, Zepbound) are available at licensed pharmacies. Compounded tirzepatide has been subject to evolving FDA guidance around shortage status; access through compounding channels varies by jurisdiction and regulatory period. Providers offering tirzepatide-based programs are indexed in the PeptideBase directory.