Comparison
Semaglutide vs Tirzepatide vs Retatrutide
Last reviewed
The three sit on a clear progression: each adds a receptor to the one before. This page compares what the published trials report and where each stands with regulators.
The short answer
Side by side
| Semaglutide | Tirzepatide | Retatrutide | |
|---|---|---|---|
| Classification | Synthetic GLP-1 receptor agonist peptide | Synthetic dual incretin receptor agonist peptide | Synthetic triple incretin receptor agonist peptide |
| CAS number | 910463-68-2 | 2023788-19-2 | 2381089-83-2 |
| Molecular formula | C187H291N45O59 | C225H348N48O68 | — |
| Molecular weight | 4113.58 g/mol | 4813.45 g/mol | ~4731 g/mol |
| Sequence | 31-residue GLP-1 analogue, Aib8 and Arg34 substituted, C18 diacid attached via an AEEA linker | 39-residue backbone with a C20 diacid fatty-acid conjugate | 39-residue backbone with a C20 diacid fatty-acid conjugate |
| Strengths | 2 mg, 5 mg, 10 mg, 15 mg, 20 mg, 30 mg, 40 mg, 50 mg | 5 mg, 10 mg, 15 mg, 20 mg, 30 mg, 40 mg, 50 mg, 60 mg, 80 mg, 100 mg, 120 mg | 5 mg, 10 mg, 15 mg, 20 mg, 30 mg, 40 mg, 50 mg, 60 mg, 100 mg |
| From, per vial | $5.50 £4.12 | $4.50 £3.37 | $8.16 £6.11 |
| From, per box of 10 | $55.00 £41.21 | $45.00 £33.71 | $81.57 £61.11 |
| Research status | An approved prescription medicine in the UK and many other countries. Supplying it as a medicine outside the regulated pharmaceutical chain is unlawful. Research-grade material is supplied here strictly as a laboratory reference material. | An approved prescription medicine in the UK and elsewhere. Supplying it as a medicine outside the regulated pharmaceutical chain is unlawful. Research-grade material is supplied here strictly as a laboratory reference material. | Investigational. In late-stage clinical trials with Eli Lilly. Not approved for any use in any country. |
In detail
What the research actually compares
Descriptions of published research activity and findings. Nothing here is a claim about what these products do, or a statement that either is safe or effective for any purpose.
The receptor progression
GLP-1 receptor activation reduces appetite and slows gastric emptying. Adding GIP appears to improve how that is tolerated rather than simply adding more of the same effect. Adding glucagon introduces an energy-expenditure pathway. The rationale for each step is that the receptors do different things, so engaging more of them may achieve more than any one alone.
What the trials reported
The STEP 1 trial of semaglutide 2.4 mg reported a mean body-weight change of about 14.9% at 68 weeks against 2.4% for placebo. SURMOUNT-1 reported up to roughly 20.9% for tirzepatide at 72 weeks. The retatrutide phase 2 trial reported up to about 17.5% at 24 weeks and up to 24.2% at 48 weeks. These are supervised clinical trials in patients, on different durations and different populations, so the figures are not directly comparable and none of them is a statement about research-grade material.
Regulatory status, which differs sharply
Semaglutide and tirzepatide are licensed medicines in the UK and many other jurisdictions, supplied here strictly as reference material for laboratory research. Retatrutide has reported phase 3 results and Eli Lilly has said it plans to file with the FDA in early 2027; it is not approved for any use in any country. Buyers are responsible for confirming that possession and use are lawful where they are.
Practical differences for laboratory work
All three are supplied as lyophilised powder in boxes of ten vials. Semaglutide is available across the widest strength range in this catalogue, from 2 mg to 50 mg. Tirzepatide spans 5 mg to 120 mg and retatrutide 5 mg to 100 mg. All three carry a C18 or C20 diacid fatty-acid conjugate that extends plasma half-life through albumin binding.
References
- 1Once-Weekly Semaglutide in Adults with Overweight or Obesity (the STEP 1 trial). N Engl J Med (2021). PMID 33567185
- 2Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med (2022). PMID 35658024
- 3Tirzepatide for Obesity Treatment and Diabetes Prevention. N Engl J Med (2025). PMID 39536238
- 4Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial. N Engl J Med (2023). PMID 37366315
Links open the record on PubMed or PubMed Central. These are citations to published research on the individual compounds, not claims about either product or about the comparison itself.
Common questions
Which produced the most weight loss in trials?
Across separate trials of different durations, retatrutide reported the highest figure at 48 weeks and tirzepatide the highest at 72 weeks. Because the trials differed in length, dose and population, the numbers cannot be compared directly, and none of them describes what research-grade material does.
Is retatrutide approved?
No. Retatrutide is investigational. It has completed phase 2 trials and is not approved for any use in any country.
Why are semaglutide and tirzepatide sold as research chemicals if they are licensed medicines?
They are supplied as reference material for laboratory research, labelled research use only and not for human consumption. That is a different legal category from supplying a medicine. Buyers must confirm that possession is lawful in their own jurisdiction.