- Generic name: Tirzepatide · Developer code: LY3298176 (Eli Lilly)
- CAS: 2023788-19-8
- Molecular weight: 4,813.5 g/mol
- Receptor targets: GLP-1R + GIPR (dual agonist)
- Peak Phase III weight loss: 20.9% at 72 weeks (15 mg/week, SURMOUNT-1)
- Approved therapeutics: Mounjaro (T2D, FDA 2022), Zepbound (obesity, FDA 2023)
- Research formats: Lyophilized vial (injectable), oral capsule
01 What Is Tirzepatide?
Tirzepatide (LY3298176) is a 39-amino acid synthetic peptide that functions as a dual agonist at both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) receptors. Developed by Eli Lilly, it represents the first approved dual incretin receptor agonist and the first approved pharmacotherapy to routinely produce greater than 20% mean body weight reduction in clinical trials.
The molecule uses a C20 fatty diacid moiety attached via a linker to enable albumin binding and extend half-life to approximately 5 days — enabling once-weekly subcutaneous dosing, similar to semaglutide. Tirzepatide was approved by the FDA for type 2 diabetes (Mounjaro) in May 2022 and for chronic weight management (Zepbound) in November 2023.
02 Dual GIP/GLP-1 Agonism Mechanism
Tirzepatide's GLP-1R agonism drives the same core effects as semaglutide: glucose-dependent insulin secretion, appetite suppression via central GLP-1R signalling, slowed gastric emptying, and glucagon suppression. What distinguishes tirzepatide is the additional GIPR co-agonism:
- Pancreatic GIPR: Synergistic enhancement of glucose-dependent insulin secretion
- Adipose GIPR: Modulation of lipid storage and mobilisation in adipose tissue
- Central GIPR: Hypothalamic appetite regulation and energy balance signalling
- Tolerability: GIP co-agonism may attenuate GLP-1-driven nausea, partly explaining tirzepatide's favourable GI tolerability profile
Crucially, the GIP and GLP-1 components appear to act synergistically rather than additively — the combined receptor engagement produces metabolic effects greater than would be predicted from either agonist alone, evidenced by tirzepatide's superior efficacy over matched-dose semaglutide despite similar GLP-1R affinity.
03 SURMOUNT Trial Programme (Obesity)
- 5 mg/week: −15.0% mean body weight (vs −3.1% placebo)
- 10 mg/week: −19.5% mean body weight
- 15 mg/week: −20.9% mean body weight
- ≥25% weight loss achieved by 36.2% of 15 mg participants
- Mean absolute weight loss: ~21 kg at 15 mg
SURMOUNT-2 (with T2D, 72 weeks) showed 12.8% and 14.7% reductions at 10 mg and 15 mg — lower than SURMOUNT-1, consistent with known attenuation of weight loss in the T2D population. SURMOUNT-3 and SURMOUNT-4 investigated maintenance of weight loss after lifestyle intervention run-in and treatment discontinuation, respectively, with SURMOUNT-4 demonstrating significant weight regain after stopping tirzepatide at 36 weeks.
SURMOUNT-5 provided the first head-to-head data against semaglutide 2.4 mg: tirzepatide 10 or 15 mg produced ~20% mean weight loss versus ~13.7% for semaglutide — a statistically significant 47% greater relative weight loss.
04 SURPASS Trial Programme (Type 2 Diabetes)
The SURPASS programme evaluated tirzepatide across 10 Phase III trials in T2D populations. Key results from SURPASS-2 (vs semaglutide 1 mg, 40 weeks, n=1,879):
- HbA1c reduction: −2.01% (5 mg), −2.24% (10 mg), −2.30% (15 mg) vs −1.86% semaglutide 1 mg
- Weight loss: −7.6 kg, −9.3 kg, −11.2 kg vs −5.7 kg for semaglutide
- Target HbA1c <7% achieved by 82–92% of tirzepatide patients vs 79% semaglutide
The SURPASS-CVOT cardiovascular outcomes trial (SURPASS-CVOT, n=13,000+) is ongoing. Interim data has not shown increased cardiovascular risk — and tirzepatide's predecessor semaglutide has demonstrated significant CV benefit in LEADER and SELECT trials.
05 Tirzepatide vs Semaglutide vs Retatrutide
| Parameter | Tirzepatide | Semaglutide 2.4 mg | Retatrutide |
|---|---|---|---|
| Receptor targets | GLP-1R + GIPR | GLP-1R only | GLP-1R + GIPR + GlucagonR |
| Peak weight loss (trials) | ~20.9% (72wk Ph III) | ~15% (68wk Ph III) | ~24.2% (48wk Ph II) |
| Approval status (2026) | Approved (T2D + obesity) | Approved (T2D + obesity) | Phase III ongoing |
| Thermogenic component | Modest (GIP) | No | Yes (glucagon) |
| Oral research format | Yes (capsule) | Rybelsus (oral semaglutide) | Capsule (investigational) |
06 Research Formats Available
Rainbow Peptide supplies tirzepatide in two research formats:
- Lyophilized vial (10mg): For injectable research protocols. Requires reconstitution with bacteriostatic water. Standard format for most in vivo and in vitro metabolic research studies.
- Oral capsule (10mg): For research protocols investigating oral GIP/GLP-1 agonism and oral bioavailability models. Note: the approved therapeutic tirzepatide is injectable — the oral capsule format is a research-only preparation.
Both formats are HPLC-verified at >98% purity with independent Certificate of Analysis. For Research Use Only.
07 Frequently Asked Questions
What is Tirzepatide?
Tirzepatide (LY3298176) is a synthetic dual agonist peptide that simultaneously activates GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) receptors. Developed by Eli Lilly, it is the active molecule in the approved medications Mounjaro (type 2 diabetes) and Zepbound (obesity). In research settings it is studied for metabolic syndrome, glycaemic regulation, cardiovascular risk, and hepatic steatosis models.
How much weight loss does Tirzepatide produce?
In the SURMOUNT-1 Phase III trial (72 weeks, n=2,539), tirzepatide produced mean body weight reductions of 15.0%, 19.5%, and 20.9% at the 5 mg, 10 mg, and 15 mg doses respectively, versus 3.1% for placebo. At 15 mg, 36.2% of participants achieved ≥25% weight loss. The SURMOUNT-2 trial in participants with T2D showed 12.8% and 14.7% reductions at 10 mg and 15 mg.
What is the difference between Tirzepatide and semaglutide?
Semaglutide (Wegovy) activates only GLP-1R. Tirzepatide adds GIPR co-agonism. The GIP component enhances insulin secretion, modulates adipose tissue lipid metabolism, and may reduce GLP-1-associated nausea — partly explaining tirzepatide's superior weight loss versus semaglutide despite both being weekly injections. In the SURMOUNT-5 head-to-head trial, tirzepatide 15 mg produced ~20% weight loss vs ~13.7% for semaglutide 2.4 mg.
How does Tirzepatide differ from Retatrutide?
Retatrutide adds a third target — glucagon receptor agonism — to the GLP-1/GIP dual agonism of tirzepatide. The glucagon component increases basal energy expenditure and promotes hepatic fat clearance. Phase II data for retatrutide showed ~24% mean weight loss at 48 weeks versus ~20% for tirzepatide 15 mg at 72 weeks in separate trials — though cross-trial comparisons require caution.
What is the mechanism of GIP receptor agonism in Tirzepatide?
GIPR (glucose-dependent insulinotropic polypeptide receptor) is expressed on pancreatic beta cells, adipocytes, bone cells, and central neurons. In the context of tirzepatide, GIPR agonism enhances glucose-dependent insulin secretion (synergistically with GLP-1R), modulates adipose lipid metabolism, and may have direct central effects on satiety and energy balance via hypothalamic GIPR signalling. The GIP component is also thought to partially attenuate GLP-1-driven nausea.
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