Tirzepatide

Quick summary

Tirzepatide is a once-weekly subcutaneous peptide that activates two related metabolic hormone receptors at the same time: the receptor for GIP (glucose-dependent insulinotropic polypeptide) and the receptor for GLP-1(glucagon-like peptide-1). It is the first approved drug in the dual-incretin class. In adults with type 2 diabetes it lowered HbA1c by roughly 2.0–2.6 percentage points and reduced body weight by 7–13 kg across the SURPASS pivotal trials.^[1]In adults with obesity but without diabetes, the SURMOUNT-1 trial reported a mean weight reduction of approximately 22.5 % at the 15 mg dose over 72 weeks.^[2]

The molecule has a mean terminal half-life of about five days, which enables once-weekly dosing. It carries the same boxed warning as the GLP-1 receptor agonist class for the risk of thyroid C-cell tumors observed in rodents, and is contraindicated in patients with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia syndrome type 2.^[7]

Discovery and development

Tirzepatide (development code LY3298176) was disclosed by Eli Lilly in 2018 as a dual GIP / GLP-1 receptor agonist designed to combine the well-established glucose-lowering and weight-reducing effect of GLP-1 receptor agonism with the insulinotropic and lipid-handling effects of GIP receptor agonism.^[5] The rationale was pharmacologically unconventional: GIP receptor agonism had previously been considered to worsen obesity, and earlier work attempted GIP receptor antagonism. The body of evidence around chronic GIP receptor signaling shifted in the mid-2010s, supporting development of co-agonists.

Tirzepatide was approved by the U.S. Food and Drug Administration as Mounjaro for type 2 diabetes in May 2022, and as Zepbound for chronic weight management in November 2023. The European Medicines Agency granted centralised marketing authorisation in September 2022 under the single brand name Mounjaro for both indications. A third indication, obstructive sleep apnea in adults with obesity, was added in the United States in December 2024. ^[7]

Structure and design

Tirzepatide is a 39 amino-acid synthetic peptide with a molecular weight of approximately 4,814 daltons. The sequence is engineered with three key modifications that distinguish it from native incretins:

• α-aminoisobutyric acid (Aib) substitutions at positions 2 and 13. Native incretins are rapidly cleaved by the enzyme dipeptidyl peptidase-4 (DPP-4) at their N-terminus; Aib substitution at position 2 creates steric hindrance that prevents this cleavage and dramatically extends serum stability.
• A C20 fatty diacid attached via a γ-glutamate / 2× AEEA linker. This lipid moiety promotes non-covalent binding to serum albumin, which shields the peptide from renal filtration and acts as a slow-release depot.
• A chimeric sequence derived from native GIP that, through specific residue choices, retains full agonism at the GIP receptor while producing biased signaling at the GLP-1 receptor (preserved insulin secretion, attenuated β-arrestin recruitment relative to native GLP-1).^[6]

The combination of N-terminal protection and albumin binding yields a mean terminal half-life of approximately 116.7 hours, supporting once-weekly subcutaneous dosing across a therapeutic range of 2.5–15 mg.

Mechanism of action

Tirzepatide engages two receptors that share a common biology but produce non-identical downstream effects. At the GLP-1 receptor, it stimulates glucose-dependent insulin secretion, suppresses glucagon, slows gastric emptying, and acts centrally to reduce appetite. At the GIP receptor, it potentiates insulin secretion and is thought to influence adipocyte lipid handling and central appetite circuits in ways that complement GLP-1 signaling.^[5],[6]

A detailed breakdown of receptor coupling, biased agonism, and dose-response data is in the dedicated article: Tirzepatide Mechanism of Action →

Pharmacokinetics in summary

• Subcutaneous bioavailability: approximately 80 %.^[7]
• Time to peak (Tmax): 24–72 hours post-dose.
• Half-life (t½): mean 116.7 hours (≈ 5 days); enables once-weekly steady-state in 4 weeks.
• Volume of distribution at steady state: approximately 10.3 L.
• Metabolism: proteolytic cleavage of the peptide backbone, beta-oxidation of the C20 fatty diacid, and amide hydrolysis. No cytochrome P450 involvement.

Detailed PK parameters, dose-titration logic, and special-population data are covered in: Tirzepatide Half-Life and Pharmacokinetics →

Pivotal clinical evidence

Two registered Phase III programs anchor tirzepatide's evidence base: SURPASS (type 2 diabetes, five core trials plus a cardiovascular outcomes trial) and SURMOUNT (chronic weight management, four core trials).

The cardiovascular outcomes trial SURPASS-CVOT (NCT04255433) is ongoing as of the last review date; full topline results will refine the place of tirzepatide in cardiovascular risk reduction relative to GLP-1 RA monotherapy.

Safety overview

The most common adverse events in pivotal trials were gastrointestinal: nausea, diarrhea, decreased appetite, vomiting, and constipation. Most were mild to moderate and attenuating with continued dosing. The product label carries a boxed warning for thyroid C-cell tumors based on rodent data, and tirzepatide is contraindicated in patients with a personal or family history of medullary thyroid carcinoma or MEN-2.^[7]

Detailed safety analysis, including signals for pancreatitis, gallbladder disease, gastroparesis, and pregnancy considerations, is in: Tirzepatide Safety Profile →

Approved indications and access

Regulatory status varies by jurisdiction; use the region switcher in the header to view the agency-specific block for your jurisdiction. As of the last review date, tirzepatide is approved in the United States, the European Union, the United Kingdom, Australia, and Canada for type 2 diabetes mellitus; chronic weight management is approved in the U.S. (as Zepbound), the EU and the U.K. (as Mounjaro for both indications), and is rolling out elsewhere. Sleep-apnea indication is U.S.-only at the time of writing.