What tirzepatide is
Tirzepatide is a synthetic, single-chain peptide of 39 amino acids that acts as an agonist at two incretin receptors at once: the glucose-dependent insulinotropic polypeptide receptor (GIPR) and the glucagon-like peptide-1 receptor (GLP-1R). It was developed at Eli Lilly under the code LY3298176 and is described in the discovery paper by Coskun and colleagues as a "GIP/GLP-1 receptor co-agonist" engineered from the GIP sequence rather than from GLP-1 [1].
Three design decisions define the molecule. The peptide backbone is based on native GIP, with substitutions that confer GLP-1 receptor activity. Two positions carry 2-aminoisobutyric acid (Aib), a non-natural residue that resists cleavage by dipeptidyl peptidase-4 (DPP-4), the enzyme that inactivates native incretins within minutes. And the lysine at position 20 carries a C20 fatty diacid attached through a linker, which binds reversibly to serum albumin and extends the circulating half-life to around five days [1, 2]. That albumin binding is why the clinical formulation is dosed once weekly.
The molecule is a white to off-white lyophilised powder in its research presentation. The reference identifiers are in the table below; the values on any given batch certificate should agree with them within the precision of the method used.
| Identifier | Value |
|---|---|
| CAS number | 2023788-19-2 |
| Development code | LY3298176 |
| Molecular formula | C225H348N48O68 |
| Molecular weight | 4813.45 g/mol (average) |
| Residues | 39 |
| Non-natural residues | Aib at positions 2 and 13 |
| Lipidation | C20 fatty diacid on Lys20 via γGlu–2×OEG linker |
| C-terminus | Amidated |
How the literature describes its mechanism
Both GIP and GLP-1 are incretin hormones: gut peptides released after a meal that potentiate glucose-dependent insulin secretion from pancreatic β-cells. GLP-1 receptor agonists have been studied clinically for two decades. GIP receptor agonism was for a long time considered a weaker or even counterproductive target, because GIP's insulinotropic effect is blunted in type 2 diabetes. The premise behind tirzepatide, set out in the discovery paper, was that combining the two signals in one molecule might produce effects on glycaemia and body weight beyond what either receptor gives alone [1].
The pharmacology is not simply "GLP-1 plus GIP". Willard and colleagues characterised tirzepatide as an imbalanced and biased agonist: at the GIP receptor it behaves much like native GIP, while at the GLP-1 receptor it is a weaker agonist that favours cAMP signalling over β-arrestin recruitment, which in cell systems translates to less receptor internalisation than native GLP-1 produces [2]. The authors proposed that this bias contributes to sustained GLP-1 receptor signalling, and they reported that in mouse islets the insulin response to tirzepatide depended on GIP receptor activity more than on GLP-1 receptor activity. Which of these properties matters most in humans is still debated in the literature, and the relative contribution of the GIP receptor to the clinical effects remains an active research question.
In practical terms for an in-vitro programme, the relevant readouts are cAMP accumulation in cells expressing GIPR or GLP-1R, receptor internalisation and β-arrestin recruitment assays, and insulin secretion from isolated islets under varying glucose. Potency values in the literature are reported as EC50 figures in the low nanomolar to picomolar range, and depend heavily on the cell system, receptor expression level and assay format, so comparisons across papers should be made with care [1, 2].
The clinical research record
Tirzepatide has one of the largest clinical trial programmes of any peptide of its generation. The two series are SURPASS, in type 2 diabetes, and SURMOUNT, in obesity and overweight, with later trials in related conditions. Summarising the headline findings:
SURPASS-1 (Rosenstock et al., The Lancet, 2021) compared tirzepatide 5, 10 and 15 mg once weekly against placebo as monotherapy in adults with type 2 diabetes over 40 weeks, and reported reductions in HbA1c and body weight at all three doses that were significantly greater than placebo [3].
SURPASS-2 (Frías et al., New England Journal of Medicine, 2021) compared the same three doses against semaglutide 1 mg once weekly over 40 weeks in 1,879 participants with type 2 diabetes on metformin. All three tirzepatide doses were non-inferior and superior to semaglutide 1 mg for HbA1c reduction, with greater weight reduction at each dose [4].
SURMOUNT-1 (Jastreboff et al., New England Journal of Medicine, 2022) enrolled 2,539 adults with obesity, or overweight with at least one weight-related complication, without diabetes. Over 72 weeks, mean body-weight change was −15.0% at 5 mg, −19.5% at 10 mg and −20.9% at 15 mg, against −3.1% with placebo [5].
SURMOUNT-2 (Garvey et al., The Lancet, 2023) studied the same question in adults with obesity and type 2 diabetes over 72 weeks, reporting mean weight reductions of 12.8% at 10 mg and 14.7% at 15 mg against 3.2% with placebo [6].
Later trials extended the programme to obstructive sleep apnoea with obesity, heart failure with preserved ejection fraction and obesity, and cardiovascular outcomes, and these are summarised in the regulatory literature for the licensed medicine. The most frequently reported adverse events across the programme were gastrointestinal: nausea, diarrhoea, decreased appetite and vomiting, mostly mild to moderate and concentrated during dose escalation [3, 4, 5, 6].
For the laboratory reader, the significance of this record is twofold. It establishes tirzepatide as a reference compound against which other dual and triple incretin agonists are compared, and it means the compound's pharmacology, pharmacokinetics and degradation behaviour are unusually well characterised in the public domain.
Regulatory status in the United Kingdom
Tirzepatide is the active ingredient of a licensed prescription-only medicine in the UK (marketed as Mounjaro), authorised by the MHRA for type 2 diabetes and for weight management under specified conditions. BuyUK Peptides does not supply that medicine, and the research-grade peptide sold here is not a medicine, is not manufactured or presented as one, and carries no therapeutic claim.
Research-grade tirzepatide is supplied as a chemical for in-vitro laboratory use under the Terms of Sale. It is not for human or veterinary administration. Purchasers must be 18 or over and are responsible for ensuring their use of the material complies with the laws and institutional rules that apply to them. Our guide to the UK rules on research compounds sets this out in more detail.
Handling, storage and stability
Tirzepatide is supplied lyophilised, sealed under nitrogen in a glass vial with a rubber stopper and an aluminium flip-off crimp. In that state it is stable for extended periods when kept cold and dark.
Sealed vial. Store at 2–8 °C for routine use. For storage beyond a few months, −20 °C or below is preferable. Protect from light. Avoid repeated freeze–thaw cycles; take the vial out once and keep it at the working temperature from then on. Allow a refrigerated vial to reach room temperature before opening, so that moisture does not condense onto the cake.
Reconstitution. For most in-vitro work the compound is reconstituted in sterile bacteriostatic water, sterile water for injection, or a buffer appropriate to the assay. Add the solvent slowly down the side of the vial rather than onto the cake, and swirl gently; do not shake, because peptides with a hydrophobic lipid chain can aggregate or foam under agitation. A lipidated peptide of this size dissolves more slowly than a short unmodified fragment; a minute or two of gentle swirling is normal. The reconstitution calculator gives the volume to add for a target concentration.
Reconstituted solution. Keep at 2–8 °C and protect from light. Lipidated GLP-1-class peptides are generally stable in aqueous solution at refrigerator temperature for several weeks, and the licensed product's label supports storage of the clinical solution at room temperature for up to 21 days once in use; for a research solution the conservative practice is to use it within 28 days and to discard it if it becomes cloudy or shows particles. Solutions should not be frozen after reconstitution unless the specific buffer has been validated for that.
Solubility. Tirzepatide is soluble in water at the concentrations used in research. The C20 diacid side chain makes the molecule amphipathic, so very high concentrations and low pH both encourage self-association. Where a solution must be filtered, use a low-binding membrane (PES or PVDF rather than nylon), because the lipid chain adsorbs to some filter materials.
What a sound certificate for tirzepatide looks like
Every batch we release carries an independent certificate of analysis, and the figures from it are transcribed on the product page and in the certificate register. For tirzepatide, a certificate should contain the following, and a reader should be able to check each item against this monograph.
Purity by RP-HPLC. Reversed-phase HPLC on a C18 column with UV detection, usually at 214 or 220 nm, reports purity as the area of the main peak as a percentage of all integrated peaks. A good batch of tirzepatide shows a single dominant peak with purity of 99% or above. Small late-eluting peaks may represent oxidised or deamidated species; a large early-eluting shoulder is more often a truncated sequence and should prompt questions.
Identity by LC-MS. Electrospray mass spectrometry confirms that the main peak has the expected mass. For tirzepatide the average molecular weight is 4813.45 Da. Electrospray produces multiply charged ions, so a certificate may report the deconvoluted mass, the most abundant charge state, or both. The observed mass should agree with the theoretical value to within a few tenths of a dalton for a deconvoluted result.
Net peptide content. Lyophilised peptides contain bound water and counter-ions, typically trifluoroacetate from purification, so the mass of powder in the vial is more than the mass of peptide. Net peptide content, where reported, expresses the fraction that is actual peptide, and it matters for preparing solutions of accurate concentration.
Endotoxin. Where the batch has been tested, a limulus amoebocyte lysate (LAL) result is reported in endotoxin units per milligram. This is relevant to cell-based assays, where endotoxin contamination can confound results.
Our guide to reading a certificate of analysis goes through a complete report line by line.
Related compounds
Tirzepatide sits in a family of incretin-receptor peptides that are frequently compared in the literature. Semaglutide is a selective GLP-1 receptor agonist, lipidated with a C18 diacid, and is the comparator in SURPASS-2. Retatrutide adds glucagon receptor agonism to the GIP and GLP-1 activity, making it a triple agonist. Cagrilintide is a long-acting amylin analogue studied in combination with semaglutide. The structural and pharmacological differences between them are the subject of our GLP-1 family comparison. Our head-to-head of tirzepatide and GLP-3 compares the dual and triple agonists directly, and semaglutide and tirzepatide are compared head to head, including the SURMOUNT-5 result.
Frequently asked questions
Is research-grade tirzepatide the same molecule as the licensed medicine? The chemical structure is the same peptide. The research material is supplied as a lyophilised powder, is not manufactured under a marketing authorisation, is not sterile unless the certificate says so, and is not for human or veterinary use.
Why does the certificate quote a different mass from the formula weight? Electrospray results are often reported as a monoisotopic mass or a particular charge state rather than the average molecular weight. Both are valid; the certificate should say which it is reporting.
Why is tirzepatide supplied in milligram quantities rather than by activity? It is a defined synthetic chemical, so it is characterised by mass and purity. Biological activity is determined by the researcher in their own assay.
How long does a sealed vial last? Lyophilised peptides of this class are stable for years at −20 °C and for many months at 2–8 °C. The batch certificate reports the test date; the storage guidance on this page applies from receipt.
References
- Coskun T, Sloop KW, Loghin C, et al. LY3298176, a novel dual GIP and GLP-1 receptor agonist for the treatment of type 2 diabetes mellitus: From discovery to clinical proof of concept. Molecular Metabolism. 2018;18:3–14. doi:10.1016/j.molmet.2018.09.009. PMID 30473097.
- Willard FS, Douros JD, Gabe MBN, et al. Tirzepatide is an imbalanced and biased dual GIP and GLP-1 receptor agonist. JCI Insight. 2020;5(17):e140532. doi:10.1172/jci.insight.140532.
- Rosenstock J, Wysham C, Frías JP, et al. Efficacy and safety of a novel dual GIP and GLP-1 receptor agonist tirzepatide in patients with type 2 diabetes (SURPASS-1): a double-blind, randomised, phase 3 trial. The Lancet. 2021;398(10295):143–155. doi:10.1016/S0140-6736(21)01324-6.
- Frías JP, Davies MJ, Rosenstock J, et al. Tirzepatide versus semaglutide once weekly in patients with type 2 diabetes (SURPASS-2). New England Journal of Medicine. 2021;385(6):503–515. doi:10.1056/NEJMoa2107519.
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). New England Journal of Medicine. 2022;387(3):205–216. doi:10.1056/NEJMoa2206038.
- Garvey WT, Frias JP, Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity in people with type 2 diabetes (SURMOUNT-2): a double-blind, randomised, multicentre, placebo-controlled, phase 3 trial. The Lancet. 2023;402(10402):613–626. doi:10.1016/S0140-6736(23)01200-X. PMID 37385275.
This monograph summarises the published literature for laboratory researchers. It is not medical advice, and nothing on this site is for human or veterinary use.