Tirzepatide

Overview

Tirzepatide is a once-weekly peptide developed by Eli Lilly under the code LY3298176. It is the first approved medicine to act as a dual agonist, activating both the GIP receptor and the GLP-1 receptor, the two main incretin pathways the gut uses to manage blood sugar and appetite after eating. It was approved as Mounjaro for type 2 diabetes in 2022 and as Zepbound for chronic weight management in 2023.

Structurally it is a 39-amino-acid peptide built on the GIP sequence, with engineered modifications that let it engage both receptors and a long fatty-acid chain that binds to albumin in the blood. That binding slows clearance and gives tirzepatide a half-life of about five days, enabling once-weekly dosing. Its clinical evidence base is large and independent, anchored by the SURPASS trials in diabetes and the SURMOUNT trials in obesity.

Approved & studied uses

Tirzepatide has approved indications and a rapidly expanding body of trial evidence:

• Type 2 diabetes: approved as Mounjaro; produces large reductions in HbA1c, often exceeding GLP-1 mono-agonists in head-to-head trials.
• Chronic weight management: approved as Zepbound for obesity, or overweight with a weight-related condition. SURMOUNT-1 reported up to roughly 20 to 22.5% body-weight reduction at the highest dose.
• Obstructive sleep apnea: approved for moderate-to-severe OSA in adults with obesity.
• Cardiovascular and metabolic endpoints: under active investigation, including heart failure with preserved ejection fraction and metabolic liver disease.
• Emerging research: studied across additional metabolic and appetite-related conditions.

Beyond approved use, tirzepatide is widely obtained through compounding pharmacies and “research” suppliers. Those products are not FDA-reviewed for purity or potency and fall outside the approved supply chain.

Mechanism of action

Tirzepatide’s distinguishing feature is that it works through two incretin receptors at once:

• Dual incretin agonism: activates both the GIP and GLP-1 receptors, rather than GLP-1 alone, which appears to enhance its metabolic and weight effects.
• Glucose-dependent insulin secretion: stimulates insulin release mainly when blood glucose is elevated, lowering the risk of hypoglycaemia on its own.
• Glucagon suppression: reduces glucagon output, decreasing the liver’s glucose production.
• Delayed gastric emptying: slows how fast food leaves the stomach, prolonging fullness after meals.
• Central appetite regulation: acts on receptors in the brain’s appetite centres to reduce hunger and overall energy intake.

The added GIP activity is what sets tirzepatide apart from pure GLP-1 drugs like semaglutide, and is thought to contribute to its larger average weight reduction.

Protocols

Quick Reference

Approved pens are pre-filled and need no mixing. The figures below apply to compounded lyophilised tirzepatide. Syringe units assume a 20 mg vial reconstituted with 1 mL BAC water (20 mg/mL) on a 1 mL / 100-unit insulin syringe.

Titration schedule

Tirzepatide follows one standard escalating schedule: start at 2.5 mg, step up by 2.5 mg roughly every 4 weeks as tolerated, then hold at the lowest dose that works. The 2.5 mg starting dose is for tolerance only, not a treatment dose. Units assume the 20 mg / 1 mL vial above (20 mg/mL).

Standard label titration (FDA Mounjaro label ↗). Approved maintenance doses are 5, 10, or 15 mg weekly; many people hold at the lowest dose that maintains results (SURMOUNT trials ↗).

Administration Routes

Tirzepatide is a once-weekly subcutaneous injection. The approved product is a pre-filled pen; compounded versions require reconstitution and self-drawing.

Reconstitution Guide

Approved pens are pre-filled and require no mixing. The steps below apply only to compounded lyophilised tirzepatide supplied as a powder. New to this? See Peptides 101 for the fundamentals.

Reconstitution Calculator

Enter your vial size, water volume, and intended dose to calculate the exact volume and syringe markings.

Active compound & chemistry

Tirzepatide is a synthetic 39-amino-acid peptide based on the sequence of GIP, engineered to activate both the GIP and GLP-1 receptors. It includes two non-standard aminoisobutyric acid (Aib) residues that resist enzymatic breakdown, a C-terminal amide, and a lysine at position 20 linked to a C20 fatty diacid that binds albumin in the blood.

Its molecular formula is C₂₂₅H₃₄₈N₄₈O₆₈ and its molecular weight is approximately 4,813.5 Da (CAS 2023788-19-2). The albumin-binding fatty-acid chain is what extends its half-life to roughly five days, allowing once-weekly dosing. Look up the compound in PubChem for full structural data, canonical SMILES, and InChI.

Evidence summary

Tirzepatide has one of the strongest, most independent evidence bases of any peptide on this site, built on large randomised trials with hard clinical endpoints.

Warnings & cautions

• Boxed warning: thyroid C-cell tumours. Tirzepatide caused thyroid C-cell tumours in rodents. It is contraindicated in anyone with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).
• Pancreatitis and gallbladder disease. Acute pancreatitis and gallbladder problems have been reported. Persistent severe abdominal pain warrants stopping and seeking care.
• Gastrointestinal side effects. Nausea, vomiting, diarrhoea, and constipation are common and dose-related, which is the reason for the gradual titration.
• Hypoglycaemia risk in combination. When used with insulin or sulfonylureas it can cause low blood sugar; those medicines may need dose adjustment.
• Not for type 1 diabetes and not a substitute for insulin. Safety in pregnancy is not established.
• Compounded products are unregulated. Purity and dose of non-pharmacy tirzepatide are not verified, raising the risk of dosing errors.