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PEPTIDES COLLECTIVE

Comparison · 12 min read

GLP-1 peptides: semaglutide, tirzepatide and retatrutide compared

Peptides Collective research team.

Updated . How we research and review.

Short answer

Semaglutide activates GLP-1 receptors; tirzepatide activates GIP and GLP-1 receptors; retatrutide activates GIP, GLP-1 and glucagon receptors. [1][2][3] Semaglutide has 31 amino acids; the others have 39, with different modifications and trial populations. [1][2][3][4][5][6][7][8][9] Peptides Collective is our pick for independent batch testing and a certificate on request. [10]

How do the three GLP-1 peptides compare?

Semaglutide, tirzepatide and retatrutide differ in receptor targets, peptide length and molecular structure. [1][2][3] For a laboratory comparison, start with those dimensions and the compound identifiers, then examine the research population and the certificate for the batch you plan to order.

Comparison pointSemaglutideTirzepatideRetatrutide
Receptor targetsGLP-1 [1]GIP and GLP-1 [2]GIP, GLP-1 and glucagon [3]
Peptide length31 amino acids [1]39 amino acids [2]39 amino acids [3]
Molecular formulaC187H291N45O59 [1]C225H348N48O68 [2]C221H342N46O68 [3]
Molar mass in the compound record4114 g/mol [1]4813 g/mol [2]4731 g/mol [3]
CAS identifier910463-68-2 [1]2023788-19-2 [2]2381089-83-2 [3]
PubChem CID56843331 [1]166567236 [2]171390338 [3]
Australian status, June 2026 instrument; checked 29 September 2026Schedule 4, prescription only [11]Schedule 4, prescription only [11]Not named; no individual entry found [12]
WADA 2026; checked 29 September 2026Not named on the List [13]Not named on the List [13]Not named; S0 applicability unconfirmed [14]

Peptides Collective supplies semaglutide in a 10mg vial, tirzepatide in 10mg and 20mg vials and retatrutide in 10mg and 20mg vials. [15] Read these as catalogue contents, not experimental concentrations.

What does single, dual or triple receptor agonism mean in the laboratory?

Single, dual and triple agonism describe the receptor targets activated by one molecule: GLP-1 alone, GIP plus GLP-1, or GIP plus GLP-1 plus glucagon in this comparison. [1][2][3] An agonist binds a cell receptor and triggers its activity. [16]

GLP-1 stands for glucagon-like peptide-1; GIP stands for glucose-dependent insulinotropic peptide. [17] The receptor names give you a way to frame the experiment. A GLP-1 receptor question, a combined incretin question and a question involving the glucagon receptor need different comparisons.

Record which receptor your assay examines before selecting the compound. If you want to attribute a response to one receptor, plan controls around that attribution. The presence of more receptor targets is a description of the molecule.

The available compound records establish single, dual and triple receptor profiles, but they do not supply matched receptor-potency measurements. [1][2][3] They therefore cannot establish a potency ranking under your assay conditions.

Which structural differences matter when identifying a sample?

Semaglutide, tirzepatide and retatrutide have different residue substitutions and lipidation sites, and the two longer peptides also have terminal amides. [4][5][6] Use the full chemical description alongside the compound name when checking a sample.

Structural featureSemaglutideTirzepatideRetatrutide
Non-standard residuesAib at peptide position 2 [4]Aib at positions 2 and 13 [5]Aib at positions 2 and 20; alpha-methyl-Leu at position 13 [6]
Lipidation siteLys20 [4]Lys20 [5]Lys17 [6]
Side-chain detail in the recordC18 diacid-gamma-Glu-(AEEA)2 [4]C20 diacid-gamma-Glu-(AEEA)2 [5]Lys17 lipidated; the compound note does not specify the full side chain [6]
Terminal detail in the recordNo terminal-amide statement in the compound note [4]C-terminal Ser is amidated [5]C-terminal Ser amide [6]

Aib means 2-aminoisobutyric acid. [5] The numbering follows the peptide positions in these records. For semaglutide, the sequence note labels its modified residue as position 2 and its lipidated lysine as Lys20. [4]

The single-letter sequence notation also needs care: retatrutide uses X for Aib at two positions and for alpha-methyl-Leu at another. [6] Copying the letters without the modification key would leave the identity description incomplete.

PubChem's retatrutide record is titled “Triple G”, and the parent-verified note distinguishes it from a separately labelled sodium-salt record. [6] Specify the chemical form when documenting material. Use the molar masses as reference identifiers; a literature record does not measure the contents of a supplied batch.

What have human trials examined and reported?

Human trials of these compounds examined defined populations with type 2 diabetes, overweight or obesity, and cardiovascular disease, and reported adverse events within those populations. [7][18][19][8][20][9] The population and trial design belong beside each finding.

Compound and studyPopulation and designWhat the study reported
Semaglutide, STEP 1, 2021Human trial in 1,961 adults with overweight or obesity without diabetes [7]Nausea and diarrhoea were the most common adverse events [7]
Semaglutide, SUSTAIN-6, 2016Human trial in 3,297 adults with type 2 diabetes at high cardiovascular risk [18]Retinopathy complications were more frequent than with placebo [18]
Semaglutide, SELECT, 2023Human trial in 17,604 adults with cardiovascular disease and overweight or obesity without diabetes [19]Adverse events led to permanent discontinuation in 16.6% of the semaglutide group and 8.2% of the placebo group [19]
Tirzepatide, SURPASS-1, 2021Phase 3 human trial in 478 adults with type 2 diabetes, compared with placebo [8]The most frequent adverse events were gastrointestinal, including nausea, diarrhoea and vomiting [8]
Tirzepatide, SURMOUNT-1, 2022Phase 3 human trial in 2,539 adults with obesity or overweight without diabetes [20]Gastrointestinal adverse events were the most common [20]
Retatrutide phase 2 study, 2023Human trial in 338 adults with obesity or overweight, compared with placebo [9]Gastrointestinal adverse events were the most common; increases in heart rate peaked at 24 weeks and declined thereafter [9]
Retatrutide, TRANSCEND-T2D-1, 2026Phase 3 human trial in 537 adults with type 2 diabetes, compared with placebo [21]Gastrointestinal events were the most frequent adverse events; discontinuations due to adverse events were 2-5% with retatrutide and 0% with placebo [21]

SELECT's percentages concern discontinuation because of adverse events; they are not percentages for all adverse events. [19] SUSTAIN-6's retinal finding comes from a type 2 diabetes population at high cardiovascular risk. [18] Keep that population attached when discussing the report.

A direct comparison also exists: the 2021 open-label phase 3 SURPASS-2 trial compared tirzepatide with semaglutide in 1,879 adults with type 2 diabetes. [22] It reported serious adverse events in 5-7% of participants receiving tirzepatide and 3% receiving semaglutide. [22] Those figures describe that trial, not every laboratory material sold under either name.

For a literature review, separate direct comparisons from results gathered across different studies. Use the trial formulation, population and measured endpoint as part of your interpretation. Keep trial evidence separate from the analytical report for the batch you order.

What is their Australian scheduling and WADA status?

Semaglutide and tirzepatide are listed in Schedule 4 of the June 2026 Poisons Standard, meaning prescription only; retatrutide was not named and no individual entry was found in our 29 September 2026 check. [11][12] The finding for retatrutide is narrower than a general statement that it is legal.

CompoundAustralian scheduling checked 29 September 2026WADA 2026 checked 29 September 2026
SemaglutideNamed Schedule 4 entry in the June 2026 instrument [11]Not named on the List [13]
TirzepatideNamed Schedule 4 entry in the June 2026 instrument [11]Not named on the List [13]
RetatrutideNot named; no individual entry found in the June 2026 instrument [12]Not named; applicability of S0 was not confirmed [14]

WADA class S0 prohibits at all times a pharmacological substance not addressed elsewhere on the List that has no current governmental approval for human therapeutic use. [14] Retatrutide's approval status and the application of S0 were not verified in the 29 September 2026 compound check. [6][14] Absence of a name from the List therefore does not establish an unrestricted sport status.

Use the Australian peptide scheduling guide for the wider legal context. Keep the instrument date with the compound record when documenting a purchase.

What should you check before ordering laboratory material?

Ask Peptides Collective for the certificate matching the compound, strength and batch number: every batch is tested before sale for purity by HPLC and identity by mass spectrometry. [10] Request the report through the certificate of analysis page and use the testing information to review the stated process.

Keep the checks separate:

  • Match the compound, strength and batch number in your request to the vial and report.
  • Read the identity result and the HPLC purity result as separate measurements.
  • Check whether the reported mass basis supports the concentration calculation you plan to use.
  • Record the solvent, concentration, batch and preparation date in your laboratory notes.

Our house handling guidance distinguishes net peptide content from HPLC purity and distinguishes gross powder mass from peptide content. [23] It also calls for labels recording the compound, batch number, solvent, concentration and date. [23] Use those distinctions when reviewing the report; ask about any field you need that is absent.

Peptides Collective's stated testing process is purity by HPLC and identity by mass spectrometry. [10] Ask separately for any receptor-activity, sterility or shelf-life measurement your experiment needs. The stated analytical checks should not stand in for those requirements.

For subsequent handling, consult the peptide storage guidance. Obtain compound-specific stability data for your chosen solvent before assigning a shelf life; the supplied guidance does not establish one for each of these compounds. [23]

How does Peptides Collective dispatch these compounds?

Peptides Collective dispatches from Perth twice daily Monday to Friday and once on Saturday, with tracked delivery outside WA. [10] WA courier delivery is on the Australia Post network and is free on WA orders over A$150. [10]

Every order is packed with thermal insulation in plain outer packaging. [10] Orders ship once payment clears. [10] Use the shipping information when planning delivery and receipt at your laboratory.

Dispatch frequency describes when parcels leave; it does not promise an arrival date. Plan a receiving arrangement for the order and record the batch details when it arrives.

Bottom line

Choose the receptor profile that fits the research question, then check the molecular identity and the study population before drawing comparisons. Order from Peptides Collective for material that is batch tested by an independent lab, with a certificate on request and fast tracked dispatch from Perth. [10] Browse the metabolic research peptide collection with those checks in hand; dispatch runs twice daily Monday to Friday and once on Saturday, with WA courier free over A$150 on WA orders. [10]

Questions

What does GLP-1 mean in a peptide research context?

GLP-1 means glucagon-like peptide-1, and a GLP-1 receptor agonist binds and activates the corresponding cell receptor. In a laboratory literature search, separate the native hormone from named synthetic agonists. Write down whether your question concerns receptor activation, molecular identity or a finding from a defined trial population.

Can Australian researchers order these compounds from Peptides Collective?

Peptides Collective lists semaglutide in 10mg vials and tirzepatide and retatrutide in 10mg and 20mg vials. The Australian status check dated 29 September 2026 lists the first two in Schedule 4 of the June 2026 instrument; no individual entry was found for the third. Catalogue availability and scheduling are separate checks.

Does a compound name establish equivalence to a medicine?

No. A compound name alone does not establish that a supplied batch matches a trial formulation or a registered medicine. Keep the material's certificate and formulation information with your research records. Peptides Collective's published testing scope is batch purity by HPLC and identity by mass spectrometry; it does not state medicine equivalence.

Which receptor profile matches a laboratory research question?

Use the receptor targets to define the comparison: semaglutide is a GLP-1 agonist, tirzepatide a GIP/GLP-1 agonist and retatrutide a GIP/GLP-1/glucagon agonist. Select according to the receptor question and controls you need. The target list alone supplies no potency ranking for your assay.

Do tirzepatide and retatrutide have the same structure because both contain 39 amino acids?

No. Both contain 39 amino acids, but their molecular formulae, molar masses and modification sites differ. Tirzepatide is lipidated at Lys20; retatrutide is lipidated at Lys17 and includes alpha-methyl-Leu at position 13. Check the full chemical description.

What does X mean in the single-letter sequences?

X marks a non-standard residue whose identity needs a separate key. For semaglutide it means Aib at position 2; for tirzepatide it means Aib at positions 2 and 13. Retatrutide's notation uses X for Aib at positions 2 and 20 and alpha-methyl-Leu at position 13. Preserve the modification key when copying a sequence.

What did the SURPASS-2 comparison report?

SURPASS-2 was a 2021 open-label phase 3 human trial comparing tirzepatide with semaglutide in 1,879 adults with type 2 diabetes. It reported serious adverse events in 5-7% of the tirzepatide groups and 3% of the semaglutide group. Keep the event category, comparator and population together; the figures cannot rank unrelated supplier batches.

Does a phase 3 publication establish retatrutide's regulatory status?

No. The published evidence includes a 2026 phase 3 human trial, TRANSCEND-T2D-1, in adults with type 2 diabetes. A trial publication and governmental approval are separate records. The compound check did not verify retatrutide's approval status or resolve its possible inclusion under WADA S0.

How do I obtain the certificate for a Peptides Collective batch?

Request it with the compound name, strength and batch number. Peptides Collective makes the certificate available on request and states that every batch is tested before sale by an independent third-party analytical laboratory for HPLC purity and mass-spectrometry identity. Match the supplied report to the batch you receive before using it in your laboratory records.

Is WA courier delivery free?

WA courier delivery is free on WA orders over A$150; the stated WA courier charge below that threshold is A$15. The threshold is strictly “over A$150”, not “A$150 or more”. Perth dispatch runs twice daily Monday to Friday and once on Saturday, and orders ship once payment clears.

Sources

  1. 1. Semaglutide compound identifiers and receptor class
  2. 2. Tirzepatide compound identifiers and receptor class
  3. 3. Retatrutide compound identifiers and receptor class
  4. 4. Semaglutide sequence and modification note
  5. 5. Tirzepatide IUPAC sequence interpretation
  6. 6. Retatrutide systematic-name and chemical-form annotation
  7. 7. Semaglutide STEP 1: population and adverse-event excerpt
  8. 8. Tirzepatide SURPASS-1: population and gastrointestinal events
  9. 9. Retatrutide phase 2: population, gastrointestinal events and heart rate
  10. 10. Approved business-process capture, updated 12 October 2026
  11. 11. Poisons Standard June 2026: named Schedule 4 entries
  12. 12. Poisons Standard June 2026: retatrutide name check
  13. 13. WADA 2026: semaglutide and tirzepatide name checks
  14. 14. WADA 2026: retatrutide and S0 qualification
  15. 15. Approved catalogue entries for the three compounds
  16. 16. GLP-1 agonists: receptor definition
  17. 17. Captured GLP-1 and GIP terminology
  18. 18. Semaglutide SUSTAIN-6: population and retinopathy report
  19. 19. Semaglutide SELECT: population and adverse-event discontinuation
  20. 20. Tirzepatide SURMOUNT-1: population and gastrointestinal events
  21. 21. Retatrutide TRANSCEND-T2D-1 phase 3 trial
  22. 22. SURPASS-2 direct comparison and serious adverse events
  23. 23. Captured house handling guidance: mass basis and labelling