# What Is Tirzepatide? The Dual GIP/GLP-1 Peptide Explained > What is tirzepatide? An FDA-approved dual GIP and GLP-1 receptor agonist for type 2 diabetes, obesity, and sleep apnea — its mechanism, approved indications, and key clinical evidence explained. ## The short version What is tirzepatide? It is an FDA-approved prescription medicine given as a once-weekly injection. Chemically, it is a synthetic peptide — a short chain of amino acids — that activates two hormone receptors in the body simultaneously: one called GIP and one called GLP-1. Both are part of the gut's normal signalling system that tells the pancreas to release insulin after a meal. Activating both together produces stronger effects on blood sugar, appetite, and body weight than activating either one alone. It was first approved in the United States in May 2022 for type 2 diabetes, then in November 2023 for weight management in adults with obesity. It has also been approved for obstructive sleep apnea in people with obesity, and trials have shown effects in fatty liver disease and heart failure. ## What is tirzepatide? The compound defined Tirzepatide (international nonproprietary name; developmental code LY3298176) is a synthetic incretin-mimetic peptide. Its 39-amino-acid backbone is engineered from the native GIP (glucose-dependent insulinotropic polypeptide) hormone sequence, with modifications that confer affinity for both the GIPR (GIP receptor) and the GLP-1R (GLP-1 receptor). A C20 fatty-diacid chain attached via a glutamic acid linker and two AEEA spacer units to a lysine side chain provides high albumin-binding affinity, slowing renal clearance and enabling once-weekly subcutaneous dosing. The two hormones it mimics — GIP and GLP-1 — are incretins: gut-derived signals released in response to nutrient ingestion that amplify the pancreatic insulin response in a glucose-dependent fashion (meaning insulin is released only when blood sugar is elevated, which makes the medication substantially safer than older insulin secretagogues that raised insulin regardless of blood glucose level). GLP-1 also suppresses glucagon (the counter-regulatory hormone), slows gastric emptying, and reduces appetite through central nervous system pathways. By engaging both receptors simultaneously, tirzepatide produces incretin effects larger than those achievable with selective GLP-1 agonism alone. In vitro assays confirmed that it engages the GIP receptor more fully than the GLP-1 receptor (an imbalanced agonist), and shows biased GLP-1 receptor signalling — meaning it preferentially activates the pathway that boosts insulin secretion (cAMP) over the pathway that dampens receptor sensitivity (beta-arrestin) [1, 2]. Tirzepatide peptide is classified under drug class A10BX16 (other blood glucose lowering drugs, excl. insulins) and carries the CAS number 2023788-19-2. ## Tirzepatide peptide — the approved indications Tirzepatide carries three FDA-approved indications as of 2024: **Type 2 diabetes mellitus** (approved May 2022): indicated as an adjunct to diet and exercise to improve glycaemic control in adults. The SURPASS phase 3 programme across multiple comparators established its superiority for HbA1c reduction versus semaglutide 1 mg (SURPASS-2, n=1,879: -2.30 vs -1.86 percentage points at 15 mg over 40 weeks) [3], versus insulin glargine, versus prandial insulin, and versus other comparators [28, 29]. **Chronic weight management** (approved November 2023): indicated for adults with a BMI of 30 or greater (obesity), or BMI of 27 or greater with at least one weight-related condition. The SURMOUNT programme established a mean weight reduction of -20.9% at 15 mg over 72 weeks in adults without diabetes (SURMOUNT-1, n=2,539) [4]. The April 2026 American College of Physicians clinical guideline designates tirzepatide as a first-line pharmacologic treatment for weight management in eligible adults [41]. **Moderate-to-severe obstructive sleep apnea in adults with obesity** (approved 2024): the SURMOUNT-OSA trial (n=469) documented an AHI reduction of 25.3–29.3 events per hour versus approximately 5 with placebo over 52 weeks [9]. The agent is not approved for type 1 diabetes. It is not approved as a weight-loss treatment for people below the BMI thresholds [7]. ## What tirzepatide is not Tirzepatide is not a selective GLP-1 receptor agonist. Its dual incretin mechanism — targeting both the GIP and GLP-1 receptors — is what distinguishes it from earlier agents in that class. The head-to-head evidence confirms this distinction is clinically meaningful: in SURMOUNT-5 in adults with obesity without diabetes, tirzepatide at the maximum tolerated dose reduced weight by -20.2% versus -13.7% with semaglutide at the maximum tolerated dose (P<0.001) [5]. Tirzepatide is not a triple agonist. It does not activate the glucagon receptor, which distinguishes it from investigational triple incretin agonists under development. It is a prescription-only medicine. The FDA label and the existing clinical evidence base apply to approved formulations dispensed by a licensed prescriber. The label does not apply to compounded formulations, which have faced FDA quality and identity warnings. --- A reading room for the published tirzepatide trial record — not a clinic, not a prescriber.