Tirzepatide
Also known as: Mounjaro, Zepbound, GIP/GLP-1 RA, Dual incretin
The first dual GIP and GLP-1 receptor agonist, demonstrating superior weight loss and glycemic control in large clinical trials.
Molecular Data
- Class
- Dual GIP/GLP-1 receptor agonist / Dual incretin mimetic
- Molecular Weight
- 4,813.48 Da
- Molecular Formula
- C₂₂₅H₃₄₈N₄₈O₆₈
- Half-Life
- ~5 days (enables once-weekly dosing)
- Sequence / Structure
- 39-amino acid dual GIP/GLP-1 agonist with C20 fatty diacid modification at Lys²⁶
Mechanism of Action
Tirzepatide is a 39-amino acid synthetic peptide that acts as a single molecule simultaneously agonizing both the glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptors. This dual-agonism is the defining pharmacological feature distinguishing it from earlier GLP-1-only agents.
GIP receptor activity: GIP is secreted from intestinal K-cells and normally accounts for approximately 50–70% of post-meal insulin secretion. GIP receptors are also expressed in adipose tissue, the brain, and bone. Tirzepatide's GIP agonism is thought to: - Synergistically enhance insulin secretion beyond GLP-1 receptor stimulation alone - Promote fatty acid uptake into adipocytes and improve adipocyte function (a counterintuitive mechanism that may reduce ectopic fat deposition) - Potentially act on central GIP receptors to reduce food intake
GLP-1 receptor activity: Similar to semaglutide — glucose-dependent insulin secretion, glucagon suppression, delayed gastric emptying, and central appetite suppression.
Why dual agonism may outperform GLP-1 agonism alone: In clinical trials, tirzepatide achieved greater HbA1c reductions and weight loss than all prior GLP-1 receptor agonists at equivalent timepoints. The exact reason for this superiority remains under active investigation but may involve GIP receptor-mediated effects on adipose tissue metabolism and enhanced central satiety signaling.
Structurally, tirzepatide uses a C20 fatty diacid modification (identical chain length to semaglutide) for albumin binding, yielding a ~5-day half-life supporting once-weekly dosing.
Research History
Tirzepatide was developed by Eli Lilly as part of a broader program to exploit dual incretin signaling following early research demonstrating that co-administration of GIP and GLP-1 receptor agonists produced additive glycemic effects.
The SURPASS clinical trial program (6 pivotal trials) evaluated tirzepatide in T2DM. SURPASS-2 (2021, NEJM) compared tirzepatide head-to-head against semaglutide 1.0 mg: all three tirzepatide doses (5, 10, 15 mg) produced significantly greater HbA1c and weight reductions than semaglutide. This was one of the first head-to-head trials demonstrating superiority of a novel agent over an established GLP-1 RA.
FDA approved tirzepatide as Mounjaro for T2DM in May 2022.
The SURMOUNT clinical trial program evaluated higher doses in obesity. SURMOUNT-1 (2022, NEJM) demonstrated mean body weight reductions of ~15%, ~19.5%, and ~20.9% at 5, 10, and 15 mg doses respectively over 72 weeks, with ~31% of participants at 15 mg achieving ≥25% body weight reduction. FDA approved tirzepatide as Zepbound for chronic weight management in November 2023.
The SURPASS-CVOT cardiovascular outcomes trial reported in 2024, showing a 15% MACE reduction in T2DM patients with established CV disease, earning tirzepatide a CV risk reduction indication.
Notable Studies
Frias JP, Davies MJ, Rosenstock J, et al. · New England Journal of Medicine
Head-to-head phase III trial (n=1,879) demonstrating tirzepatide 10 and 15 mg produced significantly greater HbA1c reductions (−2.01% and −2.30%) and weight loss (−9.3 kg and −11.2 kg) versus semaglutide 1.0 mg (−1.86% HbA1c, −5.3 kg weight).
Jastreboff AM, Aronne LJ, Ahmad NN, et al. · New England Journal of Medicine
Pivotal obesity trial (n=2,539, non-diabetic) demonstrating mean body weight reductions of 15.0%, 19.5%, and 20.9% at 5, 10, and 15 mg doses versus 3.1% placebo at 72 weeks. The largest weight loss reductions ever seen in an injectable obesity drug trial at the time.
Cardiovascular Outcomes with Tirzepatide in Type 2 Diabetes (SURPASS-CVOT)
2024Marx N, Husain M, Lehrke M, et al. · New England Journal of Medicine
Phase III cardiovascular outcomes trial (n=13,300) demonstrating 15% relative risk reduction in MACE with tirzepatide 10–15 mg versus dulaglutide in T2DM patients with established CV disease.
Tirzepatide, a New Era of Dual-Targeted Treatment for Diabetes and Obesity
2021Min T, Bain SC · Drugs
Review summarizing the pharmacology, clinical trial data, and mechanism of action of tirzepatide, contextualizing dual incretin agonism against prior GLP-1-only agents.
Research Protocols
The following protocols describe doses used in published research studies. They are not prescriptions or recommendations for human use.
Type 2 diabetes (SURPASS program dose escalation)
- Dose
- 2.5 mg → 5 mg → 10 mg → 15 mg
- Route
- Subcutaneous injection
- Frequency
- Once weekly
- Duration
- Escalation by 2.5 mg every 4 weeks to target dose
Escalation used in trials and FDA-approved Mounjaro labeling to minimize GI adverse effects.
Obesity management (SURMOUNT program)
- Dose
- 2.5 mg → escalate to 5, 10, or 15 mg
- Route
- Subcutaneous injection
- Frequency
- Once weekly
- Duration
- 20-week escalation to maintenance dose; indefinite maintenance
Dose schedule from SURMOUNT-1 and Zepbound prescribing information.