GLP-1 Research Peptides, Explained
Semaglutide, Tirzepatide and Retatrutide target overlapping but distinct receptor combinations. The difference is which receptors, not just the brand.
01The shared mechanism
All three are studied as agonists at the GLP-1 receptor — glucagon-like peptide-1, an incretin hormone receptor involved in insulin secretion, gastric emptying, and appetite signaling. Activating it is the common thread across this entire compound class.
Where they diverge is which additional receptors each one also engages.
02SM1 — GLP-1 only
Semaglutide is a single-receptor agonist: GLP-1 only. It is the most-studied compound in this class by publication volume, with the longest track record of the three, and functions as the reference point the other two are measured against.
03TZ2 — dual agonist
Tirzepatide is a dual agonist, engaging both the GLP-1 and GIP (glucose-dependent insulinotropic polypeptide) receptors. Research interest centres on whether GIP co-agonism produces effects distinct from GLP-1 stimulation alone — the two incretin pathways are studied together because they are co-secreted physiologically but have historically been investigated separately.
04R3 — triple agonist
Retatrutide extends the mechanism further, engaging GLP-1, GIP and glucagon receptors. The glucagon receptor is mechanistically distinct from the other two — it is associated with hepatic glucose output and energy expenditure rather than the incretin pathway. Retatrutide is the newest and least-published of the three, and its triple-receptor design is the primary subject of ongoing research interest.
05Why the distinction matters for research design
These are not three strengths of the same mechanism — they are three different receptor combinations that happen to share one target. A study asking whether an effect is GLP-1-specific needs Semaglutide as the clean single-agonist reference; a study of incretin co-agonism needs Tirzepatide; a study of glucagon-receptor contribution needs Retatrutide, because it is the only one of the three that engages that receptor at all.
06FAQ
What is the main difference between Semaglutide, Tirzepatide and Retatrutide?
The number of receptors each engages. Semaglutide is GLP-1 only, Tirzepatide is GLP-1 + GIP, and Retatrutide is GLP-1 + GIP + glucagon.
Is Retatrutide just a stronger version of the other two?
No. It engages an additional receptor — glucagon — that the other two do not touch at all, rather than simply activating the shared receptors more strongly.
Which compound is the right reference for a GLP-1-specific study?
Semaglutide, since it is a single-receptor agonist with no GIP or glucagon activity to confound the result.
Why is Tirzepatide studied as a dual agonist rather than two separate compounds?
Because GLP-1 and GIP are co-secreted physiologically, and the research question is often whether engaging both receptors together produces effects distinct from either alone.
Every Ethos Bio lot is analyzed by an independent third-party laboratory — HPLC purity and mass-spectrometry identity confirmation — with a batch-specific Certificate of Analysis supplied per lot.
R3 (Retatrutide) product → · TZ2 (Tirzepatide) product → · SM1 (Semaglutide) product → · R3 vs TZ2 comparison →