Retatrutide COA Verification: A Complete Lab-Testing Guide

Retatrutide COA verification comes down to eight fields, and the purity percentage is only one of them. A certificate is checkable when it names retatrutide specifically, prints a lot code that matches the vial label, names the analytical method beside every result, prints the acceptance limit each result was judged against, and carries a sample date that precedes its issue date. A certificate reporting a purity figure and none of that is a claim with nothing behind it to test. The checklist below runs in that order, cheapest check first.

Which fields make a retatrutide COA checkable?

Run them in sequence. Each one resolves to pass or fail on the document in front of you, and none of them requires access to the sample.

#	Panel	Passes when	Fails when
1	Compound identity	The certificate names retatrutide in the product field, with a CAS or molecular formula printed	A generic label such as “GLP-1 peptide,” or a template field left from another compound
2	Lot code	A lot or batch code that also appears on the vial label, character for character	No lot field, or a code the supplier cannot match to the vial that ships
3	Identity result	A mass-based result printed next to the theoretical mass it was compared against, so the difference is readable	“Identity: conforms,” with no measured value and no reference value
4	Purity result	A single figure attached to a named separation method	A bare “≥99%,” a range with no method, or a percentage with no test name
5	Specification column	Every result printed beside the acceptance limit it was judged against	Results with no limits, so nothing on the page can be failed
6	Related substances	The largest single impurity reported separately from total purity	Total purity only, which hides how the non-target fraction is distributed
7	Water content	A measured figure, because lyophilized mass includes residual water	Omitted, leaving labeled vial mass unreconciled
8	Dates and lab	Sample date, issue date, named lab, report number; sample date earlier than issue date	Dates reversed, a single undated stamp, or “independent third-party lab” with no name

The eight-point read for retatrutide COA verification. Every row is a check on the document itself, not a laboratory result; no figure in this table is drawn from a trial or a price catalog.

Panels 3 and 5 are the two that suppliers most often skip, and they are the two that make the rest falsifiable. A result with no specification beside it cannot be out of specification.

What does a reported purity percentage come to in milligrams?

Multiply and the percentage turns into mass. Target mass = vial mg × purity fraction, and the remainder is everything the certificate has not named.

Reported purity (%)	10 mg vial: retatrutide (mg)	10 mg vial: non-target (mg)	20 mg vial: retatrutide (mg)	20 mg vial: non-target (mg)
99.5	9.95	0.05	19.90	0.10
99.0	9.90	0.10	19.80	0.20
98.0	9.80	0.20	19.60	0.40
95.0	9.50	0.50	19.00	1.00

Labeled masses are the 10 mg and 20 mg vial sizes carried in a research-supply catalog at $100 and $195 respectively, priced 11 September 2026 (as of September 2026). The purity values are illustrative inputs, not measured results from any listing. Each cell is vial mg × purity fraction, with the non-target column the labeled mass minus that product.

Worked through one row: a 20 mg vial reported at 98.0% is 20 × 0.98 = 19.6 mg of retatrutide, leaving 20 − 19.6 = 0.4 mg the document has not identified. Drop half a point to 97.5% and it becomes 20 × 0.975 = 19.5 mg, with 0.5 mg unnamed.

That 0.4 mg is what panel 6 exists to describe. A total purity figure tells you the size of the non-target fraction; the related-substances table tells you whether it is one impurity at 0.4 mg or eight at 0.05 mg each, and those are different manufacturing stories with the same headline number.

Identity or purity: which panel decides it?

Identity, and the gap is not close. A purity percentage describes what proportion of the injected sample eluted as the main peak. It says nothing about what that peak is. Read panel 4 before panel 3 and a 98.0% figure quietly asserts that 9.8 mg of a 10 mg vial is retatrutide, which is the claim panel 3 was supposed to establish.

The practical consequence is that a missing identity result does not leave 2% of the vial unverified. It leaves all 10 mg unverified, because the denominator of the purity calculation is the unconfirmed compound itself. A certificate with a clean purity number and no mass comparison has documented internal consistency, not identity, which is why what each testing method actually confirms determines how much weight the percentage can carry.

Why doesn’t the trial literature settle what is in a research vial?

Because the published record describes a compound made under manufacturing controls no certificate reproduces. The phase 2 obesity trial randomized 338 adults to once-weekly subcutaneous retatrutide at 1 mg, 4 mg, 8 mg or 12 mg or placebo for 48 weeks, with percentage change in body weight from baseline to 24 weeks as the primary endpoint; least-squares mean change at 24 weeks was −7.2% in the 1 mg group, −12.9% in the combined 4 mg group, −17.3% in the combined 8 mg group and −17.5% in the 12 mg group against −1.6% on placebo, per the 2023 NEJM phase 2 retatrutide report.

The program that followed is larger still: four Phase 3 multicenter, randomized, double-blind TRIUMPH studies of weekly subcutaneous retatrutide against placebo in over 5800 participants, with percent change in body weight as the weight-management primary endpoint, according to the 2026 TRIUMPH trial design paper in Diabetes, Obesity and Metabolism. Those results attach to the material used in those trials and to nothing else. Research-supply retatrutide is sold for laboratory research use only, and its certificate is the only document connecting a given vial to any specification at all.

That is the reason the specification column matters more here than it would for an approved product. There is no monograph to fall back on, so whatever limits the issuing lab printed are the only limits that exist for that lot.

How do you check one lot against another?

Line the certificates up and compare panel 6 first, not panel 4. Total purity is the figure most likely to hold steady across lots while the impurity profile underneath it moves, so two lots both reporting 99.0% can carry different largest-single-impurity values and different water content. Reading batch-to-batch consistency across a supplier’s certificates is a comparison of the tables, not the headline.

Watch for the same lot code re-issued under a new date, which is a different failure from a reused template. A re-issue keeps every result identical and changes only the issue date; a vendor’s own purity claim reprinted as a certificate keeps the letterhead and changes the compound name. Both defeat panels 2 and 8, and the tell for the second one is font or alignment that shifts around the product and lot fields, covered under spotting an edited certificate.

The last check runs outside the document. Send the issuing lab the report number and the lot code and ask whether that record exists in their system. The report number is the single field on a certificate that the supplier does not control, which is what makes it worth an email.