GLP-1, GIP and glucagon receptor targets compared
Semaglutide, tirzepatide and retatrutide differ in how many receptors they act on: one, two and three. Whether a wider receptor profile is a better design is a question for head-to-head trials.
Three metabolic research peptides can be arranged by the number of receptors they act on: one, then two, then three. The arrangement describes a difference in design. It does not, by itself, say which design performs better.
One receptor: semaglutide and GLP-1
Semaglutide acts on the GLP-1 receptor. It is the single-target reference point in this comparison, and the other two compounds are described relative to it.
Two receptors: tirzepatide, GLP-1 and GIP
Tirzepatide acts on the GLP-1 receptor and on the GIP receptor. Compared with semaglutide, the change is the addition of a second receptor target.
Three receptors: retatrutide, GLP-1, GIP and glucagon
Retatrutide acts on the GLP-1 receptor, the GIP receptor and the glucagon receptor. It adds a third target to the two that tirzepatide engages.
A design difference, not a verdict
Adding receptors is a design choice. Whether a broader receptor profile is an improvement is an empirical question, and head-to-head trials, which compare compounds directly under the same conditions, are the tool for answering it. Receptor count alone should not be read as a ranking.
A practical way to read this literature is to take one receptor at a time: what it binds, which signaling pathway it engages, and what each study measured in its model system. Each of the three receptors can be examined that way on its own terms.