Tirzepatide: Discovery and Regulatory History

Introduction

Tirzepatide (LY3298176) is a synthetic dual incretin receptor agonist whose development traces through more than five decades of foundational research into the biology of gut-derived peptide hormones. This article presents a historical overview of the scientific and regulatory milestones from the discovery of the incretin peptides that underpin tirzepatide's pharmacology through the molecule's own development program and its sequential entry into the regulatory record. The account draws on primary literature and official regulatory documents.

Discovery Period: The Incretin Hormones

The biological concept of the incretin effect — the observation that oral glucose stimulates a substantially greater insulin response than intravenous glucose delivery of equivalent magnitude — was described in the early twentieth century, though the hormonal mediators responsible were identified over subsequent decades.

Glucose-dependent insulinotropic polypeptide (GIP) was isolated and characterized in the early 1970s by Brown and colleagues at the University of British Columbia. The peptide was initially named for its capacity to inhibit gastric acid secretion; subsequent research established that its principal physiological role was the potentiation of glucose-stimulated insulin secretion, prompting renaming to "glucose-dependent insulinotropic polypeptide." GIP is a 42-amino acid peptide secreted by enteroendocrine K cells in the proximal small intestine in response to nutrient ingestion.

Glucagon-like peptide-1 (GLP-1) was characterized in the 1980s following the molecular cloning of the proglucagon gene by Graeme Bell's laboratory at the University of Chicago in 1983. Researchers including Joel Habener, Svetlana Mojsov, Daniel Drucker, and Jens Juul Holst subsequently demonstrated that intestinal processing of proglucagon liberated GLP-1 as a biologically active peptide with potent insulinotropic activity. GLP-1 is secreted by enteroendocrine L cells of the distal small intestine and colon; its very short plasma half-life, due to rapid enzymatic inactivation by dipeptidyl peptidase-4 (DPP-4), would later drive the development of half-life-extended analogues.

Early Research: From Incretin Pharmacology to Therapeutic Candidates

The therapeutic potential of GLP-1 receptor agonism was recognized in the 1990s, as researchers demonstrated that pharmacological GLP-1 receptor stimulation could modulate glucose metabolism and reduce food intake in research models. The principal barrier to development of GLP-1-based therapies was the peptide's rapid inactivation and short half-life, properties that drove research into modified analogues and formulations capable of sustained receptor engagement — a challenge the field successfully addressed over subsequent years.

GIP research took a parallel course. While GIP receptor agonism was clearly implicated in incretin physiology, early GIP-based pharmacology did not initially produce therapeutic candidates with the same clinical traction as GLP-1R agonism. A body of preclinical research, however, indicated that the two incretin pathways were complementary and, critically, that simultaneous engagement of both receptors might produce metabolic effects that exceeded those achievable by selective GLP-1R agonism alone. This scientific rationale motivated research programs aimed at developing dual GIPR and GLP-1R agonists. Subsequent multireceptor research strategies — such as the triple agonist cagrilintide approach combining amylin and GLP-1 receptor engagement — reflect the continued expansion of this scientific field.

The foundational pharmacological characterization of tirzepatide — then designated LY3298176 — appeared in the peer-reviewed literature in 2018. Coskun and colleagues at Eli Lilly and Company reported the molecule's design, preclinical pharmacology, and early human data in Molecular Metabolism, establishing tirzepatide as a 39-amino acid GIP-sequence-based peptide with a C20 fatty diacid moiety conferring extended plasma half-life [1]. That publication marked the formal scientific introduction of the compound that would advance through one of the most extensively documented clinical development programs in incretin pharmacology.

Regulatory Milestones

Phase 1 and Phase 2 Clinical Development

Tirzepatide entered human clinical testing in phase 1 studies beginning in the late 2010s. Phase 1 data reported in the 2018 Coskun et al. paper documented pharmacokinetic properties — including a plasma half-life compatible with extended dosing intervals — that informed the dosing schedule adopted throughout subsequent clinical trials [1].

A phase 2 dose-finding study in adults with type 2 diabetes provided early evidence of dose-dependent effects on glycemic and weight-related endpoints and informed the dose selection applied across the phase 3 program. The successful phase 2 data supported progression to the large-scale SURPASS program.

The SURPASS Phase 3 Program

The phase 3 development program for tirzepatide in type 2 diabetes comprised a series of trials designated SURPASS-1 through SURPASS-5, conducted at sites internationally. Each trial enrolled adults with type 2 diabetes across different stages of the treatment continuum, comparing tirzepatide against placebo, semaglutide, insulin degludec, and insulin glargine over 40- to 52-week periods. The SURPASS trials collectively enrolled thousands of participants and generated the efficacy and safety dataset reviewed by the FDA in the course of its new drug application assessment [2,3,4].

FDA Approval: Mounjaro (May 2022)

The FDA approved tirzepatide as Mounjaro on May 13, 2022, under NDA 215866, for use as an adjunct to diet and exercise to improve glycemic control in adults with type 2 diabetes mellitus [5]. The approval was based on the SURPASS clinical trial program and designated tirzepatide as the first FDA-approved medication in the dual GIP and GLP-1 receptor agonist class — a milestone reflecting the convergence of two decades of dual-incretin research.

The SURMOUNT Phase 3 Program

A parallel phase 3 program — designated SURMOUNT — investigated tirzepatide in adults with obesity or with overweight and weight-related comorbidities beyond the type 2 diabetes indication. SURMOUNT-1 (Jastreboff et al., 2022) was a 72-week placebo-controlled trial in adults without type 2 diabetes [6]. SURMOUNT-2 (Garvey et al., 2023) examined participants with concurrent type 2 diabetes over the same duration [7]. Both trials generated the dataset reviewed by the FDA for the weight management indication.

FDA Approval: Zepbound (November 2023)

On November 8, 2023, the FDA approved tirzepatide under the brand name Zepbound for chronic weight management in adults with an initial body mass index of 30 kg/m² or greater, or 27 kg/m² or greater with at least one weight-related comorbidity, as an adjunct to a reduced-calorie diet and physical activity [8]. This approval — the second distinct FDA approval for tirzepatide — marked the first approved use of a dual GIPR and GLP-1R agonist for a weight management indication.

Subsequent Regulatory Developments

In December 2024, the FDA approved an additional indication for Zepbound for moderate-to-severe obstructive sleep apnea in adults with obesity, based on data from the SURMOUNT-OSA clinical program. This represented the first pharmacological therapy approved in the United States for that condition — a third distinct regulatory milestone for the tirzepatide program.

The FDA removed tirzepatide from its drug shortage list in 2024, reflecting the program's maturation and commercial scale-up. This development carries regulatory implications for compounding under 503A and 503B pharmacy frameworks and has been part of the regulatory discussion surrounding the compound's status in the United States. Information on synthesis standards and quality verification for research-use material is covered in the tirzepatide sourcing and quality article.

Current Research Landscape

As of the publication of this article, tirzepatide remains an active subject of investigation across a range of ongoing and recently completed clinical programs. A dedicated cardiovascular outcomes trial (SURPASS-CVOT) was registered and enrolling. Pediatric efficacy and safety data were generated in the SURPASS-PEDS trial, published in The Lancet in 2025. Investigational programs examining tirzepatide in additional cardiometabolic conditions — including metabolic dysfunction-associated steatohepatitis (MASH) and heart failure with preserved ejection fraction — have advanced through early-phase and phase 3 stages.

Tirzepatide's scientific position as the first approved dual incretin receptor agonist has generated ongoing discussion about the respective pharmacological contributions of GIPR and GLP-1R agonism, and about the broader potential of multireceptor incretin targeting as a research strategy. That discussion continues to drive both basic mechanistic studies and new clinical programs. The tirzepatide product page provides batch-specific Certificate of Analysis data for researchers sourcing the compound for non-clinical investigation.

References

1. Coskun T, Sloop KW, Loghin C, Alsina-Fernandez J, Urva S, Bokvist KB, et al. LY3298176, a novel dual GIP and GLP-1 receptor agonist for the treatment of type 2 diabetes mellitus: from discovery to clinical proof of concept. Mol Metab. 2018;18:3-14. DOI: 10.1016/j.molmet.2018.09.009

2. Rosenstock J, Wysham C, Frías JP, Kaneko S, Lee CJ, Fernández Landó L, et al. Efficacy and safety of a novel dual GIP and GLP-1 receptor agonist tirzepatide in patients with type 2 diabetes (SURPASS-1): a double-blind, randomised, phase 3 trial. Lancet. 2021;398(10295):143-155. DOI: 10.1016/S0140-6736(21)01324-6

3. Frías JP, Davies MJ, Rosenstock J, Pérez Manghi FC, Fernández Landó L, Bergman BK, et al. Tirzepatide versus semaglutide once weekly in patients with type 2 diabetes. N Engl J Med. 2021;385(6):503-515. PMID: 34170647. DOI: 10.1056/NEJMoa2107519

4. Del Prato S, Kahn SE, Pavo I, Wander PL, Chen Y, Landó LF, et al. Tirzepatide versus insulin glargine in type 2 diabetes and increased cardiovascular risk (SURPASS-4): a randomised, open-label, parallel-group, multicentre, phase 3 trial. Lancet. 2021;398(10313):1811-1824. DOI: 10.1016/S0140-6736(21)02188-7

5. US Food and Drug Administration. Mounjaro (tirzepatide) injection: NDA 215866 approval letter. May 13, 2022. Available at: https://www.accessdata.fda.gov/drugsatfda_docs/appletter/2022/215866Orig1s000ltr.pdf

6. Jastreboff AM, Aronne LJ, Ahmad NN, Wharton S, Connery L, Alves B, et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(3):205-216. PMID: 35658024. DOI: 10.1056/NEJMoa2206038

7. Garvey WT, Frías JP, Jastreboff AM, le Roux CW, Sattar N, Li T, et al. Tirzepatide once weekly for the treatment of obesity in people with type 2 diabetes (SURMOUNT-2): a double-blind, randomised, multicentre, placebo-controlled, phase 3 trial. Lancet. 2023;402(10402):613-626. DOI: 10.1016/S0140-6736(23)01200-X

8. US Food and Drug Administration. FDA approves new medication for chronic weight management. Press announcement. November 8, 2023. Available at: https://www.fda.gov/news-events/press-announcements/fda-approves-new-medication-chronic-weight-management