# What Is Tirzepatide? The Dual GIP/GLP-1 Peptide Explained > What is tirzepatide? A 39-amino-acid dual GIP/GLP-1 receptor agonist, FDA-approved for type 2 diabetes and obesity — structure, mechanism, approvals, and how it differs from GLP-1-only drugs. Classification, structure, approved indications, and how the dual-receptor design differs from first-generation incretin drugs. ## The short version Tirzepatide is a prescription medicine — a synthetic peptide approved by the FDA. It is called a 'dual incretin agonist' or 'twincretin' because it activates two separate hormone receptors that the body uses to manage blood sugar after eating: the GIP receptor and the GLP-1 receptor. Previous drugs in this class activated only the GLP-1 receptor. Tirzepatide was engineered to activate both at once with a single molecule, producing larger reductions in blood sugar and body weight than its predecessors in clinical trials. It is given once a week by subcutaneous (under the skin) injection and has a half-life of about 5 days. It is approved in the United States for type 2 diabetes, obesity, and sleep apnea. It is not approved for type 1 diabetes and is a prescription-only medicine. ## Classification and nomenclature Tirzepatide is the international nonproprietary name (INN) for the compound also known during development as LY3298176. It belongs to the drug class: dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist. Other informal names: twincretin, dual incretin mimetic, dual incretin agonist [7]. ATC code: A10BX16. CAS: 2023788-19-2. Molecular formula: C225H348N48O68. Molecular weight: 4813.53 Da. Elimination half-life: approximately 5 days. The phrase 'what is tirzepatide' is sometimes asked alongside the question of whether it is a GLP-1. The precise answer: it is not solely a GLP-1 receptor agonist — it is a dual agonist that activates both GIPR and GLP-1R. GLP-1 receptor agonism is one of its two mechanisms of action. It is also not a GLP-1 hormone itself; it is a synthetic peptide engineered from the GIP backbone [1]. ## Structure: what makes it a tirzepatide peptide A tirzepatide peptide is 39 amino acids long, built on the sequence of native GIP — the gut-derived hormone released by K-cells in the small intestine after eating. Native GIP activates only the GIP receptor. Tirzepatide's modifications allow it to also bind and activate the GLP-1 receptor [1]. The key structural innovation is the fatty-diacid arm: a C20 fatty diacid attached via a glutamic acid linker and two small polyethylene-glycol linker units (2-(2-aminoethoxy)ethoxy)acetic acid) to the lysine at position 20 of the peptide chain. This fatty-diacid arm binds reversibly to albumin (the most abundant protein in blood), which dramatically slows the peptide's removal from the body — extending the half-life to approximately 5 days and enabling once-weekly subcutaneous dosing [1]. Is tirzepatide a peptide? Yes, it is a synthetic peptide — a short chain of amino acids — not a small molecule (like many older oral diabetes drugs) and not a protein-based antibody (like many modern biologics). It is administered by subcutaneous injection, not orally, because peptides are digested in the gut if swallowed. ## FDA-approved indications and regulatory status Tirzepatide is FDA-approved as of June 2026 for three indications [7][15][33]: 1. **Type 2 diabetes mellitus** (approved May 2022): as an adjunct to diet and exercise to improve glycaemic control in adults with type 2 diabetes. 2. **Chronic weight management** (approved November 2023): as an adjunct to a reduced-calorie diet and increased physical activity in adults with obesity (BMI ≥30) or overweight (BMI ≥27) with at least one weight-related complication. 3. **Moderate-to-severe obstructive sleep apnea** in adults with obesity (approved 2024): based on SURMOUNT-OSA, which showed a reduction in the apnea-hypopnea index of 25.3-29.3 events/hour versus approximately 5 events/hour with placebo [34]. It is not approved for: type 1 diabetes; weight loss in individuals without obesity or a weight-related complication; use as the sole treatment of sleep apnea without addressing obesity. The prescribing information carries a boxed warning regarding thyroid C-cell tumours observed in rodent studies. The human relevance of this rodent signal is not established [15]. Tirzepatide is contraindicated in people with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2. ## How tirzepatide differs from earlier incretin drugs The first generation of incretin-based drugs activated only the GLP-1 receptor. Selective GLP-1 receptor agonism improves glycaemic control by stimulating insulin secretion, suppressing glucagon, slowing gastric emptying, and reducing appetite [9]. Adding GIPR activation to GLP-1R activation produces additive effects. The GIP receptor drives its own glucose-dependent insulin secretion and influences insulin resistance in adipose tissue through mechanisms partly independent of GLP-1R [10]. In obese mice without a functional GLP-1 receptor, tirzepatide still improved insulin sensitivity through GIPR signalling — demonstrating that the GIP component provides a real, weight-independent benefit [10]. In direct comparative trials, this dual mechanism translated to superior outcomes: in SURPASS-2 (1879 adults with type 2 diabetes, 40 weeks), tirzepatide was superior to semaglutide 1 mg on HbA1c reduction at all doses and produced greater body-weight reductions [3]. In SURMOUNT-5 (751 adults with obesity, 72 weeks), tirzepatide produced a mean weight change of -20.2% versus -13.7% with the comparator [5]. For a detailed account of receptor-level signalling and the structural basis of dual agonism, see [tirzepatide mechanism of action](/mechanism-of-action). --- Peer-reviewed findings on tirzepatide, summarised and cited — not a prescription, not a clinical recommendation.