Semaglutide vs Retatrutide: one receptor or three

Semaglutide is a GLP-1 receptor agonist, 31 residues, built on the human hormone. Retatrutide is a triple agonist at the GLP-1, GIP and glucagon receptors, 39 residues, built on GIP. They are 618 daltons apart and share one design feature, a fatty diacid that binds albumin.

What each one was designed to do

Semaglutide was designed to act at the GLP-1 receptor and to last. Its two edits to the native sequence, an Aib at position 8 and a lysine carrying a C18 diacid at 26, do those two jobs and nothing else.

Retatrutide was designed to act at three receptors at once. Its sequence is engineered from GIP with substitutions that let it bind GLP-1 and glucagon receptors too. In research models the glucagon receptor is the one that separates it from the tirzepatide design.

The molecules

What the report shows

The mass-spec result on a vial's report should land within a tenth of a percent of the expected mass. For semaglutide that window is about 4 daltons around 4113.6; for retatrutide, about 5 around 4731.3. The two windows are 618 daltons apart. If a vial reads in the wrong window, it is the wrong peptide, and the report says so before you open it. Look any pepuro batch up on the tracking page.

Same mass, different moles

Ten milligrams of semaglutide is 2.43 micromoles. Ten milligrams of retatrutide is 2.11. At 2 mL that is 1.22 mM against 1.06 mM. The calculator carries both molecular weights: semaglutide, retatrutide.

One receptor or three

Semaglutide is the single-receptor GLP-1 analog. Retatrutide is the three-receptor design. The mass on the report confirms which one is in the vial.

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