Overview

Tirzepatide is a 39-amino-acid synthetic peptide that functions as a dual agonist at the glucose-dependent insulinotropic polypeptide (GIP) receptor and the glucagon-like peptide-1 (GLP-1) receptor. Structurally it is based on the native GIP scaffold with substitutions and a C20 fatty-diacid moiety that binds albumin and extends the plasma half-life to roughly five days. The single-molecule dual-incretin design distinguishes it from GLP-1 monoagonists such as semaglutide.

The peptide has been the subject of the SURPASS (type 2 diabetes) and SURMOUNT (obesity) programmes of randomised trials, and reference dose-titration schedules — 2.5 mg weekly with 4-weekly step-ups to a maximum of 15 mg weekly — are drawn from those research protocols.

Mechanism (as reported in the literature)

  • Dual incretin agonism. Research suggests activation of both GIP and GLP-1 receptors produces greater glucose-dependent insulin secretion and greater body-weight reduction in animal and human studies than either receptor agonised alone.
  • Central appetite pathways. Animal studies indicate GLP-1 receptor signalling in the hypothalamus and brainstem contributes to reduced food intake; the additive role of GIP signalling in appetite is an area of active research.
  • Gastric emptying. Studies indicate tirzepatide slows gastric emptying, which contributes to postprandial glucose control and satiety in the reported literature.
  • Adipose tissue. Research characterises effects on lipolysis and adipocyte insulin sensitivity attributed to the GIP-receptor component.

Research findings

  • SURPASS programme (type 2 diabetes). Randomised phase-3 trials reported dose-dependent reductions in HbA1c and body weight relative to placebo, semaglutide 1 mg, insulin degludec, and insulin glargine (Frías et al., 2021; Ludvik et al., 2021).
  • SURMOUNT-1 (obesity, non-diabetic). A 72-week trial reported mean body-weight reductions of approximately 15%, 19.5%, and 20.9% at the 5, 10, and 15 mg weekly doses respectively (Jastreboff et al., 2022, N Engl J Med; PMID 35658024).
  • SURMOUNT-2 (obesity with type 2 diabetes). Reported mean body-weight reductions of 12.8% and 14.7% at the 10 and 15 mg doses respectively.
  • Cardiometabolic markers. Trial reports describe reductions in fasting insulin, triglycerides, and blood pressure at higher doses.

Common dosing (from published research protocols)

Published titration protocols start at 2.5 mg once weekly for four weeks and increase in 2.5 mg increments no faster than every four weeks up to a maximum of 15 mg once weekly. The 2.5 mg dose is described as a starting dose for tolerability rather than a therapeutic target. Most gastrointestinal adverse events reported in trials occurred during titration.

Reconstitution

A 10 mg tirzepatide vial reconstituted with 2 mL of bacteriostatic water yields a 5,000 mcg/mL solution. Under those conditions:

  • 2.5 mg (2,500 mcg) = 0.50 mL = 50 units on a U-100 syringe
  • 5 mg (5,000 mcg) = 1.00 mL = 100 units on a U-100 syringe
  • 10 mg (10,000 mcg) = 2.00 mL — the full vial

Use the calculator to model larger vial sizes and alternative BAC volumes.

Storage

Lyophilised tirzepatide is typically shipped refrigerated. Once reconstituted, the peptide is generally kept at 2–8 °C and used within approximately 28 days; longer-term storage of unreconstituted vials is freezer-based. Avoid freeze-thaw cycles of reconstituted solution.

  • Semaglutide — the reference GLP-1 monoagonist, useful as a mechanistic comparator.
  • Retatrutide — an investigational triple GLP-1/GIP/glucagon agonist described in a similar research literature.
  • AOD-9604 — a metabolically active peptide fragment discussed in the same body-weight research context.

Common stacks

References

  • Frías, J. P., et al. (2021). “Tirzepatide versus semaglutide once weekly in patients with type 2 diabetes.” New England Journal of Medicine, 385(6). PMID 34170647.
  • Ludvik, B., et al. (2021). “Tirzepatide versus insulin degludec in type 2 diabetes (SURPASS-3).” The Lancet, 398(10300). PMID 34370970.
  • Jastreboff, A. M., et al. (2022). “Tirzepatide once weekly for the treatment of obesity.” New England Journal of Medicine, 387(3). PMID 35658024.
  • Coskun, T., et al. (2018). “LY3298176, a novel dual GIP and GLP-1 receptor agonist for the treatment of type 2 diabetes mellitus.” Molecular Metabolism, 18. PMID 30293924.