Peptide reference · Lipidated 39-residue triple agonist peptide

Retatrutide COA check: molecular weight, formula and what to look for

By the PeptideCOACheck team · Last updated November 2, 2026 · How we check

Use these reference values to check the identity result on a Retatrutide Certificate of Analysis. The theoretical average molecular weight of Retatrutide is 4,731.35 Da and the monoisotopic mass is 4,728.472 Da.

Check a Retatrutide COA now

FP · 4,728.4718 Fingerprint calculated from the formula: positions of the protonated ions, the natural isotope pattern of the neutral molecule (relative heights are calculated; ion heights are schematic) and the atom mix. It is a reference picture, not measured data.

Retatrutide reference data

Name	Retatrutide
Also known as	LY3437943
Type	Lipidated 39-residue triple agonist peptide
Molecular formula	C₂₂₁H₃₄₂N₄₆O₆₈
Average molecular weight	4,731.35 g/mol (Da)
Monoisotopic mass	4,728.4718 Da
Residues	39
Reference source	KEGG DRUG D12430 (formula and mass cross-checked)

Expected mass spectrometry ions

A Retatrutide COA may list one of these m/z values instead of the neutral mass. That is still consistent with Retatrutide. How charge states work.

Ion	m/z (monoisotopic)	m/z (average)
[M+3H]³⁺	1,577.16	1,578.12
[M+4H]⁴⁺	1,183.13	1,183.84
[M+5H]⁵⁺	946.70	947.28
[M+6H]⁶⁺	789.09	789.57

What else can show up on a Retatrutide COA

Masses calculated from Retatrutide's formula for the adducts, degradation products and synthesis impurities a lab report can show. A match tells you what the extra peak probably is.

Signal	Value	What it means
Na adduct, deconvoluted (M + 21.98)	4,750.45 Da	Sodium adduct: an MS artifact, not a separate impurity. The [M+Na]+ ion itself is at M + 22.99
K adduct, deconvoluted (M + 37.96)	4,766.43 Da	Potassium adduct: an MS artifact. The [M+K]+ ion itself is at M + 38.96
TFA adduct (M + 113.99)	4,842.46 Da	Trifluoroacetic acid from purification seen as an adduct; residual TFA salt is real vial content

Adduct rows are deconvoluted masses (the shift seen against [M+H]⁺); the singly charged [M+Na]⁺ ion itself sits at M + 22.99. Deletion masses alone can't say which copy of a repeated residue is missing.

At over 4 kDa, Retatrutide is harder to purify; 98% or higher with one sharp main peak is a strong result. The full checklist is in how to read a peptide COA.

Retatrutide-specific things to watch

Retatrutide is an experimental 39-residue lipidated peptide with an average mass of about 4731.3 Da (monoisotopic about 4728.5 Da).

Because it is not an approved product and has been widely sold on the gray market, independent identity testing matters even more than usual. A vendor's own in-house COA is weak evidence here; look for a named third-party lab and a verifiable report ID.

Its mass is close to tirzepatide (about 4813.5 Da). A result near 4813 Da on a "retatrutide" COA indicates the wrong compound.

Retatrutide's charge states sit at 1578.1 (3+), 1183.9 (4+) and 947.3 (5+) m/z, calculated from the average mass. It is widely sold under code names such as "Reta (GLP-3)" or "GLP RT". A COA whose identity line repeats a code name without a measured mass confirms nothing.

Look for a deconvoluted mass near 4731.4 Da (average) and a lab report you can look up with the lab itself.

Compounds with similar mass

If a COA's mass is off, compare it with these neighbors. A match to one of them can point to a mislabeled product.

Tirzepatide: 4,813.45 Da (+82.10 Da)
Thymosin Beta-4: 4,963.44 Da (+232.09 Da)
Cagrilintide: 4,409.01 Da (-322.34 Da)

Sources

KEGG DRUG D12430: Retatrutide formula and reference mass.
CIAAW: Standard atomic weights: Used to calculate average molecular weights.
NIST CODATA: proton mass: Used to convert m/z charge states to neutral mass.
PeptideCOACheck methodology: How the checker's thresholds work.

Last updated November 2, 2026. Written and maintained under our editorial policy. Found an error? See corrections.

Frequently asked questions

My COA says GLP RT or GLP-3 RT. Is that retatrutide?

Only if the reported mass is near 4731.4 Da. The label alone proves nothing.

What does 1184 m/z mean on a retatrutide COA?

The 4+ ion of retatrutide.

Is retatrutide covered by the October 2026 HHS compounding policy?

No. That policy names six peptides, and retatrutide is not one of them.

For laboratory research use only. This page describes analytical chemistry data. It is not medical advice and makes no claim about effects in humans or animals.