# What Is Tirzepatide? The Dual GIP/GLP-1 Peptide Explained > What is tirzepatide? A 39-amino-acid FDA-approved dual GIP and GLP-1 receptor agonist — how it was discovered, how the dual-incretin mechanism works, and what makes it structurally distinct. From the 2018 discovery paper through FDA approval: the structure, the mechanism, the receptor pharmacology, and the history of the world's first approved unimolecular twincretin. ## The short version Tirzepatide is an FDA-approved prescription peptide medicine — a synthetic chain of 39 amino acids (the building blocks of proteins) that mimics two gut hormones at the same time. Those hormones, GIP and GLP-1, are called incretins: they are released after eating and tell the pancreas to make insulin in response to rising blood sugar. Tirzepatide activates both their receptors simultaneously — making it the first 'dual incretin agonist' (a molecule that switches on two receptors). Engaging both receptors reduces hunger more powerfully, slows the stomach more, and suppresses blood-sugar-raising hormones more effectively than targeting just GLP-1 alone. A fatty acid chain attached to the peptide backbone makes it stick to a blood protein, slowing its removal from the body so it works for about five days per injection — enabling once-weekly dosing. It was first described in 2018, and approved by the FDA for type 2 diabetes in 2022 and for weight management in 2023. ## Discovery and development — what is tirzepatide's origin? What is tirzepatide at its origin? The 2018 publication by Coskun et al. introduced LY3298176 (the development code for tirzepatide) as a novel fatty-acid-modified dual GIP and GLP-1 receptor agonist — the first candidate of its class to enter clinical development [1]. Eli Lilly researchers designed the molecule by modifying the backbone of the native GIP hormone, attaching a C20 fatty diacid (eicosanedioic acid) arm via a glutamic acid linker. That arm binds albumin — the most abundant protein in the bloodstream — slowing clearance and enabling an approximately five-day half-life that supports once-weekly dosing [7]. In the same 2018 paper, the candidate was shown to activate both GIP and GLP-1 receptor signalling in vitro and to improve glucose tolerance and reduce body weight in mice significantly more than a selective GLP-1 receptor agonist at equivalent doses. A phase 1 programme in 142 human subjects confirmed pharmacokinetics supporting once-weekly administration and showed reductions in fasting glucose and body weight versus placebo [1]. In 2020, Willard et al. characterised tirzepatide as an 'imbalanced and biased' dual agonist: it engages the GIP receptor more fully than the GLP-1 receptor, and at the GLP-1R it preferentially activates the cAMP (cyclic adenosine monophosphate — a key insulin-secretion-triggering signalling molecule) pathway over the beta-arrestin (a receptor-desensitising pathway) pathway [2]. This biased profile is proposed to sustain insulin secretion signalling longer than a balanced agonist would. ## Tirzepatide mechanism of action — the dual-incretin science To understand tirzepatide mechanism of action, start with the incretin hormones. GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) are secreted by cells in the small intestine after a meal. Both stimulate insulin secretion from the pancreatic beta cell in a glucose-dependent fashion — meaning they amplify insulin only when blood glucose is elevated, not independently. Together they account for roughly 50–70% of the insulin released in response to a meal in healthy individuals (this is the 'incretin effect' — the amplification of postprandial insulin secretion triggered by gut hormones). GLP-1 also suppresses glucagon (the pancreatic counter-regulatory hormone that raises blood glucose), slows gastric emptying, and signals the brain to reduce appetite. GIP has complementary effects on insulin secretion and also influences fat and bone metabolism. By activating both receptors simultaneously, tirzepatide engages this full dual pathway. The result of tirzepatide mechanism of action in trials versus selective GLP-1 agonism was measurably greater glucose lowering and significantly greater body-weight reduction — a clinical demonstration that the dual pathway adds incremental effect [1, 3]. A 2023 review of GIP/GLP-1 dual agonist pharmacology characterised this as the class-defining advance in incretin therapy [28]. ## Tirzepatide peptide — structure and identity The tirzepatide peptide is a 39-amino-acid linear chain, based on the native GIP sequence but with two structural modifications: (1) a fatty diacid (C20 eicosanedioic acid) arm attached via a glutamic acid linker and two (2-(2-aminoethoxy)ethoxy)acetic acid units to a lysine side chain, providing albumin-binding and the approximately five-day half-life; and (2) several amino acid substitutions in the GIP backbone that are required for balanced dual-receptor engagement and are responsible for the 'imbalanced/biased' signalling profile [2]. Key identifiers for the tirzepatide peptide: - Molecular formula: C225H348N48O68 - Molecular weight: 4,813.53 Da - CAS number: 2023788-19-2 - ATC code: A10BX16 - Synonyms: LY3298176, 'twincretin', 'dual incretin mimetic' These parameters are sourced from the compound's published pharmacology literature and prescribing documentation [1, 7]. Tirzepatide is a synthetic peptide and is not endogenous — the native incretin hormones it mimics (GIP and GLP-1) are gut-derived, but tirzepatide itself is manufactured. ## FDA approval and indications Tirzepatide received its first FDA approval in May 2022 for the improvement of glycaemic control in adults with type 2 diabetes mellitus as an adjunct to diet and exercise [6]. The November 2023 approval extended the indication to chronic weight management in adults with obesity (BMI ≥30) or overweight (BMI ≥27) with at least one weight-related condition [6]. A subsequent approval covered moderate-to-severe obstructive sleep apnea in adults with obesity, supported by the SURMOUNT-OSA trial [25]. The drug is not approved for type 1 diabetes, for cosmetic weight loss without a qualifying condition, or in paediatric populations outside specifically approved contexts. All approved formulations are prescription-only and administered by subcutaneous injection. The prescribing information is the authoritative document for indication scope, contraindications, and labelled dose schedules [6]. For a dedicated review of [tirzepatide weight loss](/weight-loss) outcomes across SURMOUNT-1, SURMOUNT-5, SURMOUNT-4, and SURMOUNT-MAINTAIN, see the dedicated page. The [Tirzepatide research](/research) page covers the full trial programme including the beyond-glycaemia indications. --- Forward-looking summaries of the published tirzepatide trial record — evidence on the page, not advice in the room.