Tirzepatide at a glance
Tirzepatide is a synthetic peptide of 39 amino acids, developed by Eli Lilly. Its chain is modelled on glucose-dependent insulinotropic polypeptide (GIP), one of the two incretin hormones, and was altered until it also activates the receptor for the other, GLP-1. That makes it a dual incretin agonist, placed between the single-receptor semaglutide and the three-receptor retatrutide. The same molecule is a licensed medicine: Mounjaro in the EU, Zepbound in the United States.
- Class: dual GIP and GLP-1 receptor agonist.
- Structure: 39 amino acids plus a C20 fatty diacid that binds albumin.
- Half-life: about five days, which supported weekly dosing in trials.
- Evidence: two large randomised programmes and an EU marketing authorisation.
How tirzepatide works
Two modifications make the peptide last. An unnatural amino acid sits where dipeptidyl peptidase-4 would normally cut the chain, and a C20 fatty diacid attaches the molecule to serum albumin. Albumin binding slows clearance by the kidney, and the half-life comes out at roughly five days.
The two receptors are not driven equally. In receptor assays tirzepatide is about as active as native GIP at the GIP receptor but weaker than native GLP-1 at the GLP-1 receptor, a pattern described as imbalanced agonism. The GLP-1 side delivers the known effects: glucose-dependent insulin release, lower glucagon, slower gastric emptying and reduced appetite through the brain.
What the GIP side adds is less clear. GIP had a poor reputation as an obesity target: its insulin effect is blunted in type 2 diabetes, and in fat tissue it favours storage. In mice, blocking the GIP receptor also lowered body weight. The better supported explanation places the useful signal in the brain, where GIP receptors in areas that govern appetite lower food intake and, in animal models, seem to soften the nausea of GLP-1 agonism. A second view holds that sustained agonism desensitises the receptor until stimulation resembles blockade. Neither is settled.
The evidence ladder for tirzepatide
| Evidence level | Model or trial | Main finding |
|---|---|---|
| Laboratory receptor assays | GIP and GLP-1 receptor activation | Comparable to native GIP at its own receptor; weaker than native GLP-1 at the other |
| Animal studies | Mouse work on GIP receptor signalling | Central GIP signalling lowered food intake and appeared to blunt nausea; blocking the receptor also reduced weight |
| Randomised trials, type 2 diabetes | SURPASS programme | HbA1c fell further than with the comparators tested |
| Randomised trial, obesity | SURMOUNT-1 (2022), 72 weeks, adults without diabetes | Mean weight change −15.0% (5 mg), −19.5% (10 mg), −20.9% (15 mg); placebo −3.1% |
| Randomised head-to-head trial | SURMOUNT-5 (2025), 72 weeks | Mean weight loss 20.2% on tirzepatide, 13.7% on semaglutide |
| Licensed medicine | Mounjaro (EU), Zepbound (United States) | EU authorisation: type 2 diabetes and weight management |
Every level of this ladder is occupied, from receptor pharmacology to a medicine assessed by the European Medicines Agency. Within SURMOUNT-1 the dose response did not flatten across the range tested. SURMOUNT-5 matters because comparisons across separate trials are weak evidence: populations, durations and lifestyle support differ. Randomising to tirzepatide or semaglutide inside one trial removed that objection for this pair.
One gap remains. None of these trials measured cardiovascular outcomes in people without diabetes; semaglutide has such a result from SELECT. No direct comparison with retatrutide exists either. Semaglutide, Tirzepatide and Retatrutide Compared puts the three records side by side.
Tirzepatide doses reported in studies
These are reference values from published trials and the approved product label, recorded as study designs. They are not guidance, and research material carries no authorisation for use in people.
| Setting | Dose | Schedule | Route | Note |
|---|---|---|---|---|
| SURMOUNT-1 (2022) | 5, 10 or 15 mg | Once weekly for 72 weeks | Subcutaneous | Compared with placebo |
| SURMOUNT-5 (2025) | Maximum tolerated dose, 10 or 15 mg | Once weekly for 72 weeks | Subcutaneous | Compared with semaglutide |
| Mounjaro label, escalation | 2.5 mg to start, then increases of 2.5 mg | One step every 4 weeks, up to 5, 10 or 15 mg | Subcutaneous | Starting dose serves adaptation |
The 2.5 mg starting dose is not there for its effect: it gives the gut time to adapt, and the trials followed the same four-week rhythm. The largest weight loss was seen in participants who got to 15 mg; those who did not tolerate the climb remained lower.
Safety findings and open questions
The safety record comes from the SURPASS and SURMOUNT trials and from licensed use. Nausea, diarrhoea, vomiting and constipation were the most frequent adverse events in every trial. Most were mild or moderate and fell during dose escalation, and some participants discontinued as a result.
Gallbladder disease was reported more often than on placebo, as happens with rapid weight loss in general. Pancreatitis was uncommon and is a label warning. Low blood sugar was rare with tirzepatide alone and more likely alongside insulin or a sulfonylurea. A small mean rise in heart rate was recorded. In rats this class produces thyroid C-cell tumours; human relevance is unproven, and regulators respond with a contraindication based on family history.
- Cardiovascular outcomes in people without diabetes have not been measured.
- What the GIP receptor contributes is unexplained: a central appetite effect, desensitisation, or both.
- The human relevance of the rodent thyroid finding is unproven.
Bench notes: storing and reconstituting tirzepatide
Tirzepatide for laboratory work comes as lyophilised powder. The storage condition given for the powder is −20 °C, in a closed vial, dry and out of the light.
To make a stock solution, bring the sealed vial to room temperature first; opening it cold draws moisture onto the powder. Bacteriostatic water suits a solution that will be sampled repeatedly, and King Peptides lists it as Bacteriostatic Water 10 ml. Add the solvent along the wall of the vial and swirl gently; do not shake. Keep a working solution refrigerated and dark. The sources give no solution stability data for tirzepatide. See Storage and Reconstitution: A Bench Protocol.
Status in the Netherlands, Belgium and Luxembourg
The European Medicines Agency has assessed tirzepatide, and it is authorised in the EU as Mounjaro for two indications: type 2 diabetes and weight management. Such an authorisation applies in the Netherlands, Belgium and Luxembourg alike. Mounjaro is prescription-only and supplied through pharmacies.
None of this extends to research material. A vial of research-grade tirzepatide has no marketing authorisation and has not been examined by any regulator; it is a chemical for laboratory work. Member states and institutions set their own rules on possession and import, so check those that apply to you.
For sport, the current WADA Prohibited List does not name tirzepatide. The list is reissued every year, so athletes should consult the version in force.
Ordering tirzepatide for research in the Benelux
King Peptides lists this peptide as Trizzy (Tirzepatide) 10 mg. It is research material, not Mounjaro.
Every lot comes with a lot-specific certificate of analysis that includes HPLC and mass spectrometry, and the shop’s lab reports page lists HPLC purity at 99% or higher for most products, tirzepatide among them. For identity, look at the mass: 4813.5 Da, as in the panel on this page. Semaglutide is some 700 Da lighter, an obvious difference; retatrutide is fewer than 100 Da away, so a low-resolution reading will not separate those two. Check that the lot number on the certificate is the one on your vial; the certificate of analysis guide explains each entry.
Parcels leave the Netherlands with tracking: usually 1–2 business days for Dutch addresses and 3–5 business days for other EU countries, which covers Belgium and Luxembourg. No customs clearance applies inside the EU. The Benelux buying guide has the supplier checklist.
Tirzepatide: quick answers
Are Mounjaro and Zepbound different molecules? No. Both are brand names for tirzepatide: Mounjaro in the EU, Zepbound in the United States.
What did SURMOUNT-5 add? A randomised comparison inside a single trial: mean weight loss of 20.2% on tirzepatide and 13.7% on semaglutide after 72 weeks. Earlier comparisons rested on separate trials.
Why does the label begin at 2.5 mg? For tolerability. The starting dose lets the gut adapt before the four-weekly steps of 2.5 mg begin.
Can a Trizzy vial stand in for Mounjaro? No. The peptide may be the same, but Mounjaro is a finished medicine with an assessed dossier and pharmacy distribution. The vial is sold for laboratory work only.
Research use only. This page describes Tirzepatide for laboratory and scientific research. Research material has no marketing authorisation, whatever the status of the molecule as a medicine elsewhere, and is not meant for human or veterinary use. Nothing on this page is medical advice; the doses above are those reported in published studies, not recommendations. Check the rules that apply in your country and at your institution before ordering.