Why everyone is talking about it: tirzepatide is the first approved drug that activates two incretin hormone receptors at once, and its clinical trials produced some of the largest average weight reductions ever reported for a medication. This briefing explains how the molecule works, what the major SURMOUNT and SURPASS trials actually measured, how it compared head-to-head with semaglutide, and what research-grade tirzepatide is (and is not).
What is tirzepatide?
Tirzepatide is a 39-amino-acid synthetic peptide developed by Eli Lilly. Its backbone is based on GIP (glucose-dependent insulinotropic polypeptide), modified so that it also activates the GLP-1 receptor. A C20 fatty diacid chain attached to the peptide binds albumin in the blood, which slows clearance and gives it a half-life of about five days.
It is approved in Canada and other countries under the brand names Mounjaro and, in some markets, Zepbound. Those are prescription medicines. Research-grade tirzepatide, like TrueLabs TZ-2, is a laboratory reagent and not approved for human use.
| Class | Dual GIP / GLP-1 receptor agonist |
|---|---|
| Length | 39 amino acids + C20 fatty diacid |
| Molecular weight | ~4813.5 Da |
| Half-life | ~5 days (albumin binding) |
| Developer | Eli Lilly (development code LY3298176) |
Why “dual agonist” matters
Incretins are gut hormones released after eating. Two of them dominate the research:
- GLP-1 boosts glucose-dependent insulin release, slows stomach emptying and acts on appetite centres in the brain. Semaglutide is a GLP-1-only agonist.
- GIP also boosts insulin release and appears to influence fat tissue and energy balance. Its role was long debated, because GIP signalling alone seemed weak in type 2 diabetes.
Tirzepatide was designed to test a hypothesis: that hitting both receptors would outperform GLP-1 alone. The clinical program that followed is the main reason incretin biology is now one of the most active fields in metabolic research.
SURMOUNT: the obesity trials
SURMOUNT-1 (Jastreboff et al., New England Journal of Medicine, 2022) enrolled about 2,500 adults with obesity or overweight without diabetes, and followed them for 72 weeks alongside lifestyle intervention.
| Group | Average body-weight change at 72 weeks |
|---|---|
| Placebo | about −3% |
| Lowest tirzepatide dose group | about −15% |
| Middle dose group | about −19.5% |
| Highest dose group | about −21% |
Later SURMOUNT trials examined people with type 2 diabetes (SURMOUNT-2), the effect of an intensive lifestyle lead-in (SURMOUNT-3) and what happens when treatment stops (SURMOUNT-4, where much of the lost weight was regained after switching to placebo).
SURPASS: the diabetes trials
The SURPASS program tested tirzepatide in type 2 diabetes against placebo, insulin glargine, insulin degludec and semaglutide. Across the program, tirzepatide lowered HbA1c (a three-month average of blood sugar) and body weight more than each comparator. These results led to its first approvals, for glycemic control in type 2 diabetes.
Tirzepatide vs semaglutide
Two trials compared the molecules directly:
- SURPASS-2 (Frías et al., NEJM, 2021): in type 2 diabetes, all tirzepatide doses lowered HbA1c and body weight more than semaglutide 1 mg over 40 weeks.
- SURMOUNT-5 (NEJM, 2025): in adults with obesity without diabetes, tirzepatide produced an average weight reduction of about 20% versus about 14% with semaglutide over 72 weeks.
| Tirzepatide | Semaglutide | |
|---|---|---|
| Receptors | GIP + GLP-1 | GLP-1 only |
| Backbone | GIP-based | GLP-1-based |
| Half-life | ~5 days | ~7 days |
| Head-to-head result | Tirzepatide ahead on weight and HbA1c in SURPASS-2 and SURMOUNT-5 | |
What the trials reported on tolerability
The most common adverse events reported across the programs were gastrointestinal: nausea, diarrhea, vomiting and constipation, mostly mild to moderate and most frequent during dose escalation. Like other incretin drugs, the prescription product carries warnings in its official labelling. Anyone considering medication for weight or blood sugar should talk to a doctor or pharmacist; only a prescriber can assess whether it is appropriate.
Important: the results above come from controlled clinical trials of the pharmaceutical product under medical supervision. They describe the science of the molecule, not the effect of any research-grade material.
Research-grade tirzepatide in Canada
Labs studying incretin signalling, receptor pharmacology or the GIP/GLP-1 hypothesis use research-grade tirzepatide as a reference compound. TrueLabs supplies it as TZ-2, lyophilized powder in vials from 5 to 60 mg, shipped from inside Canada with a batch-specific COA. Because it is a large, modified peptide (~4813.5 Da), a mass spectrometry identity check matters more than usual; see how to read a peptide COA.
Researchers studying amylin as a complementary satiety pathway also use cagrilintide, the amylin analogue tested in combination with semaglutide.
Frequently asked questions
Cliquez sur une question pour afficher la réponse.
What is tirzepatide?
A 39-amino-acid peptide that activates both the GIP and GLP-1 receptors. It is the active ingredient of the prescription medicines Mounjaro and Zepbound.
How much weight did people lose in SURMOUNT-1?
Average body-weight reductions were roughly 15% to 21% across tirzepatide dose groups over 72 weeks, compared with about 3% for placebo.
Is tirzepatide stronger than semaglutide?
In the head-to-head SURPASS-2 and SURMOUNT-5 trials, tirzepatide produced larger average reductions in body weight and HbA1c than semaglutide.
Is research-grade tirzepatide the same as Mounjaro?
No. Mounjaro is an approved prescription drug. Research-grade tirzepatide is a laboratory reagent sold for research use only.
Related reading
- Tirzepatide side effects by dose
- Is retatrutide safe? The full safety analysis
- Research peptides in Canada: complete guide
- How to store peptides
- NAD+ and metabolism research guide
Selected research references
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity. N Engl J Med. 2022;387(3):205–216. PubMed
- Frías JP, Davies MJ, Rosenstock J, et al. Tirzepatide versus semaglutide once weekly in patients with type 2 diabetes. N Engl J Med. 2021;385(6):503–515. PubMed
- Aronne LJ, et al. Tirzepatide as compared with semaglutide for the treatment of obesity (SURMOUNT-5). N Engl J Med. 2025. PubMed
- Aronne LJ, et al. Continued treatment with tirzepatide for maintenance of weight reduction (SURMOUNT-4). JAMA. 2024. PubMed
TrueLabs products are sold for in vitro and laboratory research use only. They are not intended for human or veterinary use. This article summarizes published clinical research for educational purposes and is not medical advice. Please speak with a doctor or pharmacist about any health question.