Tirzepatide and Retatrutide Side by Side: Two Incretin Receptors or Three
The field went from compounds that hit only the GLP-1 receptor, to tirzepatide with two targets, to retatrutide with three, in a short span of years. Because the two newer agents arrived so close together they tend to be discussed as a pair. For study design, though, what separates them matters more than what they share: their receptor pharmacology differs, and so does the depth of evidence behind each.
Picking one for a study
- Need a comparator that is approved and fully characterized? Use tirzepatide.
- Asking what the glucagon receptor contributes, how energy expenditure changes, or how triple agonism behaves pharmacologically? Use retatrutide.
- Need a one-receptor baseline against either of them? Use semaglutide, covered in the semaglutide notes.
How much evidence stands behind each
Tirzepatide’s clinical record is complete. SURPASS covered diabetes and SURMOUNT covered obesity, and in SURMOUNT-1 the highest dose produced average weight loss of up to about 21% across 72 weeks. That result showed two-receptor agonism beating GLP-1 alone on weight outcomes.
Retatrutide, by contrast, rests on phase 2. Those results appeared in the New England Journal of Medicine in 2023: about 24% mean weight loss at 48 weeks on the top dose, with the curve still falling at the final visit. No incretin had posted a stronger mid-stage figure. The phase 3 readouts have not arrived, so the compound’s profile is built on a few hundred trial participants, where tirzepatide’s draws on tens of thousands.
The glucagon component
What makes retatrutide scientifically interesting is its action at the glucagon receptor. Activating that receptor increases energy expenditure and pushes the liver to burn fat; in phase 2 sub-studies, liver fat dropped markedly. The historical worry with glucagon agonists was high blood sugar, and in retatrutide the GIP and GLP-1 activity seem to counterbalance it. Phase 3 will test whether the balance survives at scale. Until then, in vitro studies comparing receptor signaling between the two compounds continue.
Pharmacology at a glance
Structurally the two are close relatives. Each is a 39-amino-acid peptide carrying a C20 fatty-diacid, and each has kinetics that suit once-weekly use. The differences lie in which receptors they engage and how strongly:
| Retatrutide | Tirzepatide | |
|---|---|---|
| Receptors engaged | Three: GIP, GLP-1, glucagon | Two: GIP, GLP-1 |
| Relative strength | Highest at GIP, middling at glucagon, deliberately weak at GLP-1 | Full agonist at GIP; at GLP-1, less active than the native hormone |
| Where it stands | Phase 3 (TRIUMPH); no approval in any country | Approved in type 2 diabetes and in obesity |
Handling is the same for both, and the same as for semaglutide: these are large lipidated peptides, so reconstitute gently, keep them refrigerated and never shake them.
Tirzepatide and retatrutide at LiliPeptide
Listings: Tirzepatide in 5mg, 10mg, 15mg, 20mg, 30mg, 40mg, 50mg, 60mg, 100mg and 120mg; Retatrutide in 5mg, 10mg, 15mg, 20mg, 30mg, 40mg, 50mg, 60mg and 100mg; and, for a baseline arm, Semaglutide in 5mg, 10mg, 15mg, 20mg and 30mg.
These Freedom Diagnostics Testing reports appear on our COAs page:
- Tirzepatide 30mg: batch LIL812026BLK, tested 23 Sep 2026, report LILI2609210551
- Retatrutide 10mg: batch entry “Clear Blue Cap”, tested 31 Aug 2026, report Lili2608270160
- Retatrutide 20mg: batch entry “July 21, 2026”, tested 15 Sep 2026, report Lili2609140593
- Retatrutide 30mg: batch RT30, tested 5 Jun 2026, report Lili2606030201
Each report applies only to the sample it names. Other strengths of either compound, and semaglutide, have no report on that page. For research use only. Not for human or veterinary use.
