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Tirzepatide

Tirzepatide: A GIP / GLP-1 Dual Receptor Agonist

Research summary. Tirzepatide is a once-weekly synthetic peptide developed by Eli Lilly that acts as a dual agonist at the gastric inhibitory polypeptide (GIP) receptor and the GLP-1 receptor. It was approved by the FDA in 2022 as Mounjaro for type 2 diabetes and in 2023 as Zepbound for chronic weight management, becoming the first GIP/GLP-1 dual agonist to reach the market. Tirzepatide produced larger reductions in HbA1c and body weight than GLP-1 monoagonists in head-to-head trials and represents a substantial pharmacological step beyond the GLP-1 monoagonist class.

Molecular profile

  • Class: GIP / GLP-1 dual receptor agonist (peptide)
  • Sequence: 39-residue peptide with C20 fatty-diacid conjugation at Lys20, several Aib substitutions, and balanced GIP/GLP-1 receptor engagement
  • Molecular formula: C₂₂₅H₃₄₈N₄₈O₆₈
  • Molecular weight: ~4813.5 g/mol
  • PubChem CID: 156588324
  • CAS number: 2023788-19-2
  • Synonyms: LY3298176; Mounjaro (T2D brand); Zepbound (obesity brand)
  • Half-life: Approximately five days, supporting once-weekly subcutaneous dosing

Mechanism of action

Tirzepatide combines two complementary incretin mechanisms in a single peptide:

  • GLP-1 receptor agonism. Glucose-dependent insulin secretion, glucagon suppression, delayed gastric emptying, and central appetite suppression — the established GLP-1 mechanism shared with semaglutide and liraglutide.
  • GIP receptor agonism. Additional glucose-dependent insulin release and effects on adipose-tissue insulin sensitivity. The role of GIP receptor agonism in tirzepatide's superior weight-loss profile has been an active area of mechanistic investigation, with the receptor's activity in CNS appetite regulation and in adipose-tissue lipid handling both implicated.
  • GIP-favoured affinity. Tirzepatide binds GIP receptor with affinity comparable to native GIP and GLP-1 receptor with somewhat lower affinity than native GLP-1. The "imbalanced" receptor engagement is believed to contribute to the favourable efficacy-and-tolerability profile.
  • Fatty-diacid conjugation. The C20 fatty-diacid conjugation supports albumin binding and substantially extends plasma half-life, enabling once-weekly subcutaneous dosing.

Clinical research highlights

SURPASS programme (T2D). Phase 3 SURPASS trials demonstrated tirzepatide's efficacy in type 2 diabetes. In SURPASS-2 (Frías et al., NEJM 2021), tirzepatide produced HbA1c reductions of 2.0–2.3 percentage points versus 1.9 for semaglutide 1 mg, with greater weight loss across all tirzepatide doses. SURPASS-1 through SURPASS-5 supported the FDA approval of Mounjaro in 2022.

SURMOUNT programme (obesity). SURMOUNT-1 (Jastreboff et al., NEJM 2022) reported placebo-subtracted weight reductions of 17.8% at the 15 mg dose in adults with obesity over 72 weeks — substantially exceeding GLP-1 monoagonist comparators. SURMOUNT-2 in T2D-with-obesity, SURMOUNT-3 in continued-weight-loss extension, and SURMOUNT-4 in maintenance-of-weight-loss supported the FDA approval of Zepbound in 2023.

SURMOUNT-OSA. A trial in obstructive sleep apnoea reported substantial reductions in apnoea-hypopnoea index with tirzepatide in adults with obesity and moderate-to-severe OSA, supporting an FDA label expansion for OSA in 2024.

Cardiovascular outcomes (SURPASS-CVOT). A long-term cardiovascular outcomes trial comparing tirzepatide to dulaglutide is ongoing.

Adverse-effect profile. Adverse effects in clinical trials have been broadly consistent with the incretin-agonist class, dominated by gastrointestinal effects (nausea, diarrhoea, vomiting) particularly during dose escalation.

Current research status

Tirzepatide is FDA-approved as Mounjaro (2022) for type 2 diabetes and as Zepbound (2023) for chronic weight management, with subsequent label expansion for obstructive sleep apnoea (2024). It is administered via once-weekly subcutaneous injection.

Research-peptide supply of tirzepatide is broadly available, but the regulated drug product is the appropriate channel for clinical use. Research-grade material is for laboratory and animal-model use only.

Key takeaways for researchers

  • Tirzepatide is a once-weekly GIP / GLP-1 dual receptor agonist developed by Eli Lilly.
  • It is FDA-approved as Mounjaro (2022, T2D), Zepbound (2023, obesity), and with label expansion for obstructive sleep apnoea (2024).
  • Phase 3 results reported HbA1c reductions exceeding 2 percentage points and placebo-subtracted weight reductions of approximately 18% at the highest dose, exceeding GLP-1 monoagonist comparators.
  • The GIP-receptor mechanism contributes meaningfully to the differentiated efficacy profile.
  • Research-grade tirzepatide is for laboratory use only and is not a substitute for the regulated drug product.

References

  1. Frías JP, Davies MJ, Rosenstock J, et al. Tirzepatide versus semaglutide once weekly in patients with type 2 diabetes. N Engl J Med. 2021;385(6):503–515.
  2. Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(3):205–216.

This article is provided for educational and research purposes only. Tirzepatide research material is supplied for laboratory use and is not intended for human consumption outside of approved, regulated drug products (Mounjaro, Zepbound). It is not intended for diagnosis, treatment, cure, or prevention of any disease or condition. All work involving this peptide should be conducted by qualified personnel within an appropriate research setting and in compliance with applicable institutional and regulatory requirements.

Tirzepatide | BonesLabs