What is tirzepatide?

Tirzepatide is a lipidated synthetic peptide that acts as an agonist at both the glucose-dependent insulinotropic polypeptide (GIP) receptor and the glucagon-like peptide-1 (GLP-1) receptor. Eli Lilly and Company developed it, and its 2018 discovery paper describes a fatty acid modified peptide with dual GIP and GLP-1 receptor activity. ^[1] A later Lilly paper states that tirzepatide was discovered by engineering GLP-1 activity into the GIP sequence. ^[3]

That origin explains the name researchers use for its class. GIP and GLP-1 are incretins, gut hormones released after a meal that act on the pancreas. Tirzepatide is a single molecule built to reach both receptors, which is why reviews call it a dual incretin agonist. ^[10]

Three facts shape everything else about tirzepatide. It is a peptide. It carries a fatty acid chain that keeps it in circulation for days. And almost all of the published human evidence comes from one sponsor's clinical programme. Research-grade tirzepatide in 10mg and 20mg vials is in stock with a batch certificate.

Tirzepatide binds and activates two G protein-coupled receptors: the GIP receptor and the GLP-1 receptor. In Lilly's binding studies it bound the GIP receptor with a Ki of 0.135 nM and the GLP-1 receptor with a Ki of 4.23 nM. The paper describes the first as comparable to native GIP and the second as approximately 5-fold weaker than native GLP-1. ^[1]

A 2020 study in JCI Insight took the analysis further and gave the molecule its two most-quoted descriptors: imbalanced and biased. ^[3]

• Imbalanced. Receptor occupancy calculations showed greater engagement of the GIP receptor than the GLP-1 receptor.
• Biased. At the GIP receptor, tirzepatide mimicked native GIP. At the GLP-1 receptor it favoured cAMP generation over beta-arrestin recruitment and drove less receptor internalisation than GLP-1 itself.

The same group reported, in primary islets, that beta-arrestin 1 limited the insulin response to GLP-1 but not to GIP or tirzepatide. The authors proposed that the biased signalling contributes to the insulin secretion seen with the molecule. Most of those authors were Lilly employees, which the paper declares. ^[3]

In cell lines and mice, the 2018 discovery paper reported that tirzepatide activated both receptor pathways, produced glucose-dependent insulin secretion and reduced food intake and body weight in mice to a greater extent than a selective GLP-1 receptor agonist. ^[1] Those are animal and cell results. They describe the pharmacology researchers then set out to test in people.

Tirzepatide is a 39-amino-acid linear peptide with two non-coded residues, a fatty diacid side chain and an amidated C-terminus. Lilly's discovery paper gives the architecture: a C20 fatty diacid is attached through a linker to the lysine at position 20, positions 2 and 13 carry Aib (alpha-aminoisobutyric acid), and the C-terminal serine is amidated. ^[1]

The identifiers come from PubChem ^[4] and the architecture from the discovery paper. ^[1] We checked each value on 29 September 2026 and decoded the one-letter sequence from PubChem's IUPAC name, where the two Aib residues appear as 2-methylpropanoyl units.

Two details trip people up. First, PubChem holds more than one record for tirzepatide with the same formula. CID 166567236 is the record that carries the CAS number. Second, the two molecular weights differ by about 2.5 units because they come from different calculations: PubChem lists 4813, and the Lilly paper reports 4810.52 Da. When you compare a mass spectrometry result on a certificate against a published value, know which figure the lab used.

The fatty diacid is what sets the half-life. In the phase 1 study the mean half-life was approximately 5 days (116.7 hours). ^[1] Lilly attributes that to albumin binding enabled by the acylation, and the Australian product information reports tirzepatide as 99% bound to plasma albumin and metabolised by proteolytic cleavage of the backbone, beta-oxidation of the C20 diacid and amide hydrolysis.

Tirzepatide has been examined in large randomised human trials, plus the cell and mouse work that preceded them. The SURPASS programme studied adults with type 2 diabetes, the SURMOUNT programme studied adults with obesity or overweight, and later trials examined obstructive sleep apnoea, heart failure with preserved ejection fraction and cardiovascular outcomes. Unlike most research peptides, tirzepatide has large human trials behind it.

SURPASS ran to five core trials. Australian Prescriber's December 2023 review tabulates SURPASS-1 to 5 with 478, 1,879, 1,444, 2,002 and 475 participants, against placebo, semaglutide and two basal insulins. ^[15] Those five trials are the basis of the original Australian registration for type 2 diabetes.

Every finding above describes what a trial reported for its own population, using the sponsor's pharmaceutical product under trial conditions. None of it is a claim about a research vial.

The tirzepatide evidence base is deep on clinical endpoints and thin on independence. Each phase 3 trial in the table lists Eli Lilly as the funder, and Lilly staff appear among the authors of the pharmacology papers. ^[5][14] Sponsor funding is normal for a new medicine. A careful reader should still know that almost no large tirzepatide trial comes from an independent group.

Four limits are worth stating plainly.

1. Head-to-head trials against semaglutide were open label. SURPASS-2 and SURMOUNT-5 both say so in their methods. ^[6][13] Participants and investigators knew which drug was given.
2. Cardiovascular outcomes are narrower than headlines suggest. SURPASS-CVOT showed tirzepatide was noninferior to dulaglutide, an active comparator with its own cardiovascular data. The superiority test did not reach significance (P = 0.09). ^[14] In SUMMIT, the composite difference came from worsening heart-failure events (8.0% against 14.2%), while cardiovascular death occurred in 2.2% on tirzepatide against 1.4% on placebo, with a wide confidence interval. ^[12]
3. Duration is measured in weeks to about two years. Most trials ran 40 to 72 weeks. SUMMIT had a median follow-up of 104 weeks. ^[12]
4. No published trial used research-grade material. Every human study used the manufacturer's product. Purity, identity and peptide content of any research vial are a separate question, which is exactly what a batch certificate exists to answer.

Gastrointestinal events were the most common adverse events in every trial reviewed here, mostly rated mild to moderate. In SURPASS-1, nausea occurred in 12% to 18% of tirzepatide participants against 6% on placebo, diarrhoea in 12% to 14% against 8%, and vomiting in 2% to 6% against 2%. ^[5]

The trials also recorded these events:

• Head-to-head with semaglutide (SURPASS-2): nausea 17% to 22% against 18%, diarrhoea 13% to 16% against 12%, vomiting 6% to 10% against 8%. Serious adverse events were reported in 5% to 7% of tirzepatide participants and 3% of semaglutide participants. Hypoglycaemia below 54 mg per decilitre occurred in 0.2% to 1.7% of tirzepatide participants. ^[6]
• Obesity (SURMOUNT-1): adverse events led to discontinuation in 4.3% to 7.1% of the three tirzepatide groups against 2.6% on placebo. Most gastrointestinal events occurred during the escalation phase. ^[7]
• Heart failure (SUMMIT): adverse events, mainly gastrointestinal, led to discontinuation in 6.3% on tirzepatide against 1.4% on placebo. ^[12]
• Type 2 diabetes monotherapy (SURPASS-1): no clinically significant or severe hypoglycaemia was reported with tirzepatide. ^[5]
• Animal data: tirzepatide caused thyroid tumours in rats, and it is not known whether this happens in humans. ^[8] The Australian product information describes the rat finding as C-cell tumours seen at all tested exposures in a 2-year study, with human relevance unknown, and lists acute pancreatitis and gallbladder disease among reported adverse reactions.

A 2024 review in Drugs summarised the SURPASS data as mostly mild to moderate adverse events led by nausea, diarrhoea, decreased appetite and vomiting. ^[10] These are clinical-trial observations in specific trial populations, reported as the published record.

Tirzepatide is listed in Schedule 4 of the Poisons Standard (prescription only). The entry sits in the June 2026 Poisons Standard instrument (F2026L00633), which commenced on 1 June 2026, and the instrument's index also links tirzepatide to Appendix L. ^[2]

It is also a registered prescription medicine. The Australian product information gives a date of first approval of 23 December 2022, and Australian Prescriber's December 2023 review lists the original approved indication as insufficiently controlled type 2 diabetes in adults. ^[15] The current Australian consumer information, revised in 2026, adds weight management in adults with overweight or obesity and moderate to severe obstructive sleep apnoea in adults with obesity.

For sport, tirzepatide is not named on the WADA 2026 Prohibited List, which took effect on 1 January 2026. ^[9] The list's S0 class covers pharmacological substances with no current governmental approval for human therapeutic use; tirzepatide holds such approval in Australia. The List is revised every year, so check the current edition before relying on this.

Scheduling is compound-specific. Semaglutide carries its own Schedule 4 entry, while retatrutide has no entry in the June 2026 instrument. Our guide to Australian peptide law and the Poisons Standard explains what each schedule means.

Tirzepatide sits between semaglutide and retatrutide in receptor count: semaglutide targets one receptor, tirzepatide two and retatrutide three. All three are lipidated peptides built for a long half-life, and they differ in length, targets, evidence stage and Australian scheduling.

The tirzepatide column is drawn from the sources above. ^[4][2] The other columns come from the same PubChem, Poisons Standard and WADA checks we ran for each compound on 29 September 2026.

Two direct comparisons exist between tirzepatide and semaglutide, both open label: SURPASS-2 in type 2 diabetes and SURMOUNT-5 in obesity without diabetes. ^[6][13] The full breakdown is in semaglutide vs tirzepatide. No published trial compares tirzepatide with retatrutide directly; tirzepatide vs retatrutide sets out how their structures and trial programmes differ. Both sit in our metabolic research peptides range.

Tirzepatide's only published storage conditions describe the manufacturer's solution: refrigerated, protected from light, and not frozen. MedlinePlus lists refrigeration at 36 to 46 degrees Fahrenheit (about 2 to 8°C) in the original carton to protect from light. ^[8] The Australian product information gives the same 2 to 8°C range and says not to freeze.

Research tirzepatide ships as lyophilised powder, and no published stability study covers research-grade material. Use the manufacturer's solution data as the reference point for a reconstituted solution: cold, dark and unfrozen. For lyophilised vials, keep them sealed, cold and dry until use.

On solvents, the only primary-source detail is from Lilly's discovery work, where tirzepatide was synthesised with standard peptide chemistry and dissolved in phosphate-buffered saline for preclinical assays. ^[1] We stock BAC Water (sterile water with 0.9% benzyl alcohol) for laboratory reconstitution. Our peptide storage guide covers temperatures, light, freeze-thaw and labelling for lyophilised and reconstituted peptides.

Peptides Collective sells tirzepatide for laboratory research use only, in 10mg vials from A$98 and 20mg vials at A$168. Stock ships from Western Australia with tracking.

Every batch is tested by an independent lab before it goes on sale. The certificate reports purity by HPLC and identity by mass spectrometry, and it is published under the batch number printed on the vial. You can search the certificate of analysis library by that batch number and match the report to the vial in your hand.

Read the certificate against the structure table above. The identity result should correspond to a peptide of about 4813 g/mol, and our guide on how to read a peptide certificate of analysis explains the HPLC trace, the mass spectrum and net peptide content. The tirzepatide product page links the certificate for the current batch.

Tirzepatide is a 39-amino-acid, albumin-binding peptide that activates the GIP and GLP-1 receptors, with a half-life of about 5 days. Its clinical record is large, recent and almost entirely funded by its developer. In Australia it is a Schedule 4 substance and a registered prescription medicine, and WADA's 2026 List does not name it. For a research vial, the batch certificate is the evidence that settles what is in the vial.