Tirzepatide: what it is, how it works and what studies have found

Tirzepatide is a single peptide that activates two incretin receptors. Instead of building on GLP-1, its designers started from GIP (glucose-dependent insulinotropic polypeptide), added GLP-1 receptor activity, and attached a C20 fatty di-acid for once-weekly exposure. This overview covers its structure, receptor pharmacology, half-life, development history, the main SURPASS and SURMOUNT findings, and how the molecule is characterised in the laboratory. It reports published findings only and is not medical or usage guidance.

What is tirzepatide?

Tirzepatide is a once-weekly GIP receptor and GLP-1 receptor agonist. It “is based on the GIP sequence and contains aminoisobutyric acid (Aib) in positions 2 and 13, a C-terminal amide, and Lys residue at position 20 that is attached to 1,20-eicosanedioic acid via a linker” [1]. It was discovered and developed under the code LY3298176, first described as “a fatty acid modified peptide with dual GIP and GLP-1 receptor agonist activity designed for once-weekly subcutaneous administration” [9].

It is the active ingredient of approved medicines for type 2 diabetes, chronic weight management, obstructive sleep apnoea in adults with obesity, and cardiovascular risk reduction in type 2 diabetes in the US, and is authorised in the EU [1] [2] [5].

Tirzepatide structure and sequence

Property	Tirzepatide
INN	Tirzepatide
Development code	LY3298176 [9]
CAS number	2023788-19-2 [6] [8]
UNII	OYN3CCI6QE [6]
Molecular formula	C225H348N48O68 [1] [7]
Molecular weight	4813.53 Da (label); 4813.45 (KEGG) [1] [7]
Monoisotopic mass	About 4810.52 Da [7] [8]
Length	39 amino acids, linear [9]
Sequence (one-letter)	Y-Aib-EGTFTSDYSI-Aib-LDKIAQ-K-AFVQWLIAGGPSSGAPPPS-NH2 [6] [7]
Non-coded residues	Aib at positions 2 and 13 [1] [9]
Side chain	Lys20 acylated with a C20 fatty di-acid (1,20-eicosanedioic acid) through a γGlu-2×OEG linker [1] [6]
C-terminus	Serine amide [1] [6]
Albumin binding	99% [1]

Two points matter for anyone characterising the molecule. First, the label and the FDA substance record give the linker only as “a linker” and as a systematic name; read as building blocks, the side chain is γ-glutamate, two 8-amino-3,6-dioxaoctanoic acid (OEG) units and eicosanedioic acid, which is the composition that reproduces the published formula C225H348N48O68 [1] [6]. Second, published mass values differ by basis: the average molecular weight is 4813.53 Da in the US label and 4813.45 in KEGG, while the 4810.52 Da quoted as the molecular weight in the discovery paper matches the monoisotopic mass, so specifications should state which value and basis they use [1] [7] [8] [9].

Tirzepatide mechanism of action

Tirzepatide “selectively binds to and activates both the GIP and GLP-1 receptors, the targets for native GIP and GLP-1” [1]. The label describes the downstream effects: enhanced first- and second-phase insulin secretion, reduced glucagon, both in a glucose-dependent manner; increased insulin sensitivity in a hyperinsulinaemic euglycaemic clamp study after 28 weeks; and delayed gastric emptying that is largest after the first administration and diminishes over time [1].

Receptor pharmacology in vitro

Measure (HEK293 cells)	GIP receptor	GLP-1 receptor	Comparison with native hormone	Ref
Binding affinity (Ki)	0.135 nM	4.23 nM	GIPR comparable to native GIP; GLP-1R about 5-fold weaker than GLP-1	[9]
cAMP potency (EC50)	0.0224 nM	0.934 nM	GIPR similar to GIP; GLP-1R about 13-fold weaker than GLP-1	[9]

These numbers explain why tirzepatide is described as “imbalanced”. Receptor-occupancy modelling at clinically efficacious exposures showed greater engagement of the GIP receptor than the GLP-1 receptor [10]. The same work found that tirzepatide mimics native GIP at the GIP receptor but is biased at the GLP-1 receptor, favouring cAMP generation over β-arrestin recruitment and driving less receptor internalisation than GLP-1. In primary islets, β-arrestin1 limited the insulin response to GLP-1 but not to GIP or tirzepatide, which the authors propose as one way the bias could enhance insulin secretion [10]. This is in vitro and ex vivo evidence; how much each receptor contributes to clinical effects in humans remains an open research question.

In mice, tirzepatide improved glucose tolerance by acting on both receptors, and with chronic administration decreased body weight and food intake more than a selective GLP-1 receptor agonist [9].

Tirzepatide half-life

Parameter	Value	Evidence level	Ref
Mean half-life	About 5 days (116.7 h)	Phase 1, healthy subjects and type 2 diabetes	[9]
Elimination half-life	Approximately 5 days	Approved US label	[1]
Time to maximum concentration	8 to 72 h after subcutaneous administration	Approved US label	[1]
Absolute bioavailability (subcutaneous)	80%	Approved US label	[1]
Apparent clearance	0.061 L/h	Approved US label	[1]
Steady state	Reached after 4 weeks of once-weekly administration	Approved US label	[1]
Metabolism	Proteolytic cleavage, beta-oxidation of the C20 di-acid, amide hydrolysis; no intact drug in urine or faeces	Approved US label	[1]

The C20 fatty di-acid “enables albumin binding and prolongs the half-life” [1]. For context, semaglutide (C18 di-acid) has a labelled half-life of about 1 week [22].

Development history and timeline

Tirzepatide was discovered and developed by Eli Lilly and Company. The discovery paper characterised LY3298176 in vitro, in mice and in a three-part phase 1 programme in which 142 people received at least one administration of tirzepatide, dulaglutide or placebo [9].

Date	Milestone	Ref
2018	Discovery-to-proof-of-concept paper and 26-week phase 2 trial in type 2 diabetes published	[9] [11]
2020	Imbalanced, biased dual-agonist pharmacology described	[10]
2021	SURPASS-1, SURPASS-2 and SURPASS-4 published	[12] [13] [14]
13 May 2022	First US approval (type 2 diabetes), NDA 215866, new molecular entity	[3]
2022	SURMOUNT-1 published	[16]
15 Sep 2022	EU marketing authorisation	[5]
8 Nov 2023	US approval for chronic weight management, NDA 217806 (priority review)	[4]
20 Dec 2024	New-indication supplement on NDA 217806; label now includes moderate to severe obstructive sleep apnoea in adults with obesity	[2] [4]
2025	SUMMIT, SURMOUNT-5 and SURPASS-CVOT published	[15] [18] [20]
27 Aug 2026	New-indication supplement on NDA 215866; label now includes cardiovascular risk reduction in type 2 diabetes	[1] [3]

Tirzepatide clinical trials: key studies and findings

SURPASS is the type 2 diabetes programme and SURMOUNT the weight-management programme; SUMMIT studied heart failure with preserved ejection fraction. Dose levels are deliberately omitted below; where a trial had several tirzepatide arms, the range across arms is given.

Study	Phase / design	Population	n	Duration	Primary endpoint	Main finding	Ref
Phase 2 (2018)	2, placebo and dulaglutide controlled	Type 2 diabetes	318	26 weeks	HbA1c change	−1.06 to −1.94 points vs −0.06 placebo; dulaglutide −1.21	[11]
SURPASS-1	3, placebo-controlled monotherapy	Type 2 diabetes, injectable-naive	478	40 weeks	HbA1c change	−1.87 to −2.07 points vs +0.04 placebo	[12]
SURPASS-2	3, open-label vs semaglutide	Type 2 diabetes	1,879	40 weeks	HbA1c change	−2.01 to −2.30 vs −1.86; noninferior and superior	[13]
SURPASS-4	3, open-label vs insulin glargine	Type 2 diabetes, high CV risk	2,002	52 to 104 weeks	HbA1c change at 52 weeks	−2.43 and −2.58 vs −1.44; MACE-4 HR 0.74 (0.51–1.08)	[14]
SURPASS-CVOT	3, double-blind vs dulaglutide	Type 2 diabetes with ASCVD	13,165 analysed	Event-driven	CV death, MI or stroke	12.2% vs 13.1%; HR 0.92 (0.83–1.01); noninferior	[15]
SURMOUNT-1	3, placebo-controlled	Obesity or overweight, no diabetes	2,539	72 weeks	% weight change	−15.0% to −20.9% vs −3.1%	[16]
SURMOUNT-4	3, randomised withdrawal	Obesity or overweight, no diabetes	670 randomised	36-week lead-in + 52 weeks	% weight change weeks 36–88	−5.5% continued vs +14.0% switched to placebo	[17]
SURMOUNT-5	3b, open-label vs semaglutide	Obesity, no diabetes	751	72 weeks	% weight change	−20.2% vs −13.7%	[18]
SURMOUNT-OSA	3, two placebo-controlled trials	Moderate to severe OSA with obesity	Two trials	52 weeks	AHI change	−25.3 vs −5.3 and −29.3 vs −5.5 events/h	[19]
SUMMIT	3, placebo-controlled	HFpEF with BMI ≥30	731	Median 104 weeks follow-up	CV death or worsening HF; KCCQ-CSS	9.9% vs 15.3% (HR 0.62); KCCQ-CSS +19.5 vs +12.7	[20]

SURPASS: type 2 diabetes

The 2018 phase 2 trial randomised 318 people with type 2 diabetes to tirzepatide, dulaglutide or placebo for 26 weeks. The HbA1c effect was dose-dependent and did not plateau, ranging from −1.06% to −1.94% across the tirzepatide arms, compared with −0.06% for placebo and −1.21% for dulaglutide [11].

In SURPASS-1, 478 people with type 2 diabetes managed by diet and exercise were randomised at 52 centres in India, Japan, Mexico and the USA. At 40 weeks HbA1c fell by 1.87% to 2.07% with tirzepatide against a rise of 0.04% with placebo, and body weight fell by 7.0 to 9.5 kg [12].

SURPASS-4 compared tirzepatide with insulin glargine in 2,002 people with type 2 diabetes and elevated cardiovascular risk. At 52 weeks the two arms tested for the primary endpoint lowered HbA1c by 2.43% and 2.58% versus 1.44% with glargine. Hypoglycaemia was less frequent (6–9% vs 19%), and adjudicated MACE-4 events were not increased (HR 0.74, 95% CI 0.51–1.08) [14].

SURPASS-CVOT then tested cardiovascular outcomes against an active comparator. Among 13,165 patients with type 2 diabetes and atherosclerotic cardiovascular disease, cardiovascular death, myocardial infarction or stroke occurred in 801 (12.2%) on tirzepatide and 862 (13.1%) on dulaglutide (HR 0.92, 95.3% CI 0.83–1.01). Tirzepatide met the noninferiority margin (P=0.003) but superiority was not established (P=0.09) [15].

SURMOUNT: weight management and related conditions

SURMOUNT-1 randomised 2,539 adults with obesity, or overweight with at least one weight-related complication and no diabetes, to tirzepatide or placebo for 72 weeks. Mean baseline weight was 104.8 kg. Mean weight change was −15.0%, −19.5% and −20.9% in the three tirzepatide arms versus −3.1% with placebo, and 50% and 57% of participants in the two higher-dose arms lost 20% or more of body weight, compared with 3% on placebo [16].

SURMOUNT-4 addressed what happens when treatment stops. After a 36-week open-label lead-in with a mean weight reduction of 20.9%, 670 participants were randomised to continue tirzepatide or switch to placebo. From week 36 to week 88 weight changed by −5.5% with continued tirzepatide and +14.0% with placebo; the authors concluded that withdrawal led to substantial regain [17].

SURMOUNT-OSA ran two trials in moderate to severe obstructive sleep apnoea with obesity, with baseline apnoea-hypopnoea index (AHI) of about 50 events per hour. At week 52, AHI fell by 25.3 versus 5.3 events per hour in trial 1 (no positive airway pressure) and by 29.3 versus 5.5 in trial 2 (on positive airway pressure) [19]. In SUMMIT, among 731 patients with heart failure with preserved ejection fraction and obesity, cardiovascular death or worsening heart failure occurred in 9.9% versus 15.3% (HR 0.62, 95% CI 0.41–0.95); the effect was driven by worsening heart-failure events, and cardiovascular deaths were few (8 vs 5) [20].

Tirzepatide vs semaglutide

Two randomised head-to-head trials exist. In SURPASS-2, 1,879 people with type 2 diabetes received one of three tirzepatide arms or semaglutide for 40 weeks. HbA1c change was −2.01 to −2.30 percentage points with tirzepatide versus −1.86 with semaglutide, so every tirzepatide arm was noninferior and superior, and weight reductions were greater by 1.9 to 5.5 kg [13]. In SURMOUNT-5, 751 adults with obesity but without diabetes received the maximum tolerated level of either drug for 72 weeks: weight change was −20.2% with tirzepatide and −13.7% with semaglutide, and waist circumference fell by 18.4 versus 13.0 cm [18].

Structurally the two molecules differ in backbone (GIP-based 39-mer versus GLP-1-based 31-mer), lipid (C20 versus C18 di-acid) and receptor profile (dual versus single). Our semaglutide vs tirzepatide vs liraglutide comparison sets out the analytical differences, and the semaglutide overview covers the GLP-1 analogue in detail.

Safety findings reported in studies

The US label lists nausea, diarrhoea, decreased appetite, vomiting, constipation, dyspepsia and abdominal pain as the most common adverse reactions (≥5%) [1]. In trials, gastrointestinal events were mostly mild to moderate and clustered during dose escalation: in SURPASS-1, nausea occurred in 12–18% versus 6% with placebo [12]; in SURPASS-2, nausea was 17–22% with tirzepatide and 18% with semaglutide, and serious adverse events 5–7% versus 3% [13]. In SURMOUNT-1, adverse events caused discontinuation in 4.3–7.1% of tirzepatide participants versus 2.6% on placebo [16].

Other reported findings:

• Thyroid C-cell tumours (rats): tirzepatide causes thyroid C-cell tumours in rats; whether it does so in humans is unknown, and the label carries a boxed warning [1].
• Pancreatitis: acute pancreatitis has been observed in patients treated with tirzepatide [1].
• Hypoglycaemia: no clinically significant or severe hypoglycaemia was reported with tirzepatide monotherapy in SURPASS-1 [12]; rates were lower than with insulin glargine in SURPASS-4 [14].

Regulatory status by region

Region	Status	Ref
United States	Approved: type 2 diabetes (2022; label now includes paediatric patients 10 years and older and cardiovascular risk reduction); chronic weight management (2023); obstructive sleep apnoea with obesity	[1] [2] [3] [4]
European Union	Authorised 15 Sep 2022; EMA therapeutic areas: type 2 diabetes, obesity, overweight	[5]
Japan	Marketed products listed under the JAN name	[7]
Other markets	Status varies by country; check the national register

Tirzepatide in laboratory research

As a dual agonist with published receptor constants, tirzepatide is used as a reference compound in incretin pharmacology. Common research applications include:

• Receptor signalling: GIPR and GLP-1R cAMP accumulation and binding assays in recombinant cell lines, as in the discovery work [9].
• Biased agonism: β-arrestin recruitment and receptor internalisation assays comparing tirzepatide with native GLP-1 [10].
• Islet and in vivo studies: primary islet insulin secretion and mouse models of body weight, food intake and glucose tolerance [9] [10].
• Analytical characterisation: reversed-phase HPLC or UPLC for purity and related substances, LC-MS for intact mass (monoisotopic mass about 4810.52 Da [8]), peptide mapping to confirm both Aib positions and the Lys20 side chain, and water, acetate and peptide-content tests.

How is tirzepatide made? Synthesis, purity and impurities

The discovery paper states that the peptides “were synthesized at Eli Lilly and Company using traditional peptide chemistry methods” [9]. For a 39-residue peptide with two hindered Aib residues and a lipidated lysine, that normally means Fmoc solid-phase peptide synthesis (SPPS), sometimes in hybrid schemes with fragment couplings, followed by preparative reversed-phase HPLC and lyophilization. The general trade-offs between solid-phase, liquid-phase and hybrid routes are explained in SPPS vs LPPS.

Typical impurity classes for this structure are deletion and insertion sequences from incomplete or double couplings, truncated chains, diastereomers from racemisation, side-chain variants (missing or partial OEG or γGlu units), deamidation of the glutamine residues and oxidation of tryptophan. The EU synthetic peptide guideline, effective 1 June 2026, lists deletion, truncated and insertion sequences among the impurity types to characterise and control [21]. For specification setting and thresholds see peptide API impurities and specifications.

Storage and stability of lyophilized tirzepatide

Tirzepatide for research and API use is supplied as a white to off-white lyophilized powder (the lyophilisation step removes water to slow hydrolysis and aggregation). Winhycare’s specification is storage at −20 °C, protected from light and moisture. For the underlying science of dry-powder stability, moisture uptake and handling vials in the laboratory, see lyophilised peptide stability and storage.

Tirzepatide versus related peptides

Property	Tirzepatide	Semaglutide	Retatrutide
Receptors	GIPR, GLP-1R [1]	GLP-1R [22]	GIPR, GLP-1R, glucagon receptor [23]
Length	39 residues [9]	31 residues [22]	39 residues
Lipid	C20 di-acid on Lys20 [1]	C18 di-acid on Lys26 [22]	C20 di-acid on Lys17
Half-life	About 5 days [1]	About 1 week [22]	About 6 days [23]
Status (Oct 2026)	Approved (US, EU) [3] [5]	Approved (US, EU) [5]	Investigational, phase 3

Retatrutide adds glucagon receptor agonism to a related GIP-based design; see the retatrutide overview for its structure and phase 3 results.

How Winhycare Pharma supplies tirzepatide

Winhycare Pharma supplies tirzepatide as research-use-only material for laboratories and, separately, as API to licensed pharmaceutical manufacturers. Material is supplied at ≥99% purity by HPLC with a certificate of analysis for every batch, and custom synthesis (specified salt forms, purity grades, reference-standard quantities) is available. Specifications are on the tirzepatide supplier page; to request a quotation, use the peptide API enquiry form.

For laboratory research use only. Not for human or veterinary use.