How do I know if my tirzepatide is real?

Test a sample from your own vial or batch. Mass spectrometry should show a mass matching tirzepatide, 4813.53 average or 4810.52 monoisotopic. HPLC then shows how much of the material is that molecule, and an amount test compares the milligrams present with the label. Packaging, powder colour and a seller's certificate cannot tell you which peptide is inside or how much.

What mass should a tirzepatide COA show?

4813.53 g/mol average, the figure in the FDA label, or 4810.52 Da monoisotopic, the figure PubChem calculates and the 2018 discovery paper quotes. Both are right; the report should say which one it compared against and print the measured value beside it. A measured value far from both points to a different or modified molecule, and should be questioned before any purity figure is accepted.

Can a high HPLC purity prove my vial is tirzepatide?

No. HPLC purity is the share of the main peak among the peaks the method detects. A vial of clean semaglutide or retatrutide labelled as tirzepatide would also give one tall peak and a high percentage. Only a mass measurement says which molecule made that peak, so read purity after identity, and treat a purity figure with no identity result as incomplete.

Does a tirzepatide certificate from the seller count as proof?

It counts as a claim to check. Confirm the certificate names the same batch as your vial, names the laboratory and the analysis date, and can be verified with the issuer. Even a genuine certificate describes the sample that laboratory received, which may not be your vial. Our COA checker walks through each line, and a third-party lab test on your own sample settles it.

One of the 30 compound testing profiles

Tirzepatide

Tirzepatide is a 39-amino-acid peptide (C225H348N48O68, average mass 4813.53 g/mol) with a C20 fatty diacid attached to lysine 20; a test should confirm that mass, then report HPLC purity and the milligrams actually present in the vial.

Tirzepatide is a synthetic peptide agonist of the GIP and GLP-1 receptors and the active ingredient of Mounjaro, a prescription medicine approved by the US FDA (Mounjaro prescribing information, section 11).

Test your tirzepatide

Identity card

Formula: C225H348N48O68
Average mass: 4,813.53 g/mol
Monoisotopic mass: 4,810.52 Da
Length: 39 residues
Modifications: Aib (alpha-aminoisobutyric acid) at positions 2 and 13, shown as X in the sequence; Lys20 attached through a linker to a C20 fatty diacid (1,20-eicosanedioic acid); C-terminal amide
Also sold as: Tirz, TZP
Sequence: YXEGTFTSDYSIXLDKIAQKAFVQWLIAGGPSSGAPPPS
Note: The average mass of 4813.53 is the figure printed in the FDA label. PubChem rounds the same formula to 4813 g/mol and gives a monoisotopic mass of 4810.5248574 Da, recorded here as 4810.52. PubChem holds several compound records with this formula; CID 166567236 is the first match for the name tirzepatide and lists it as its first synonym. The one-letter sequence is from KEGG DRUG D11360.

Source: PubChem CID 166567236 (synonym: tirzepatide), Mounjaro (tirzepatide) prescribing information, section 11 Description, KEGG DRUG D11360, Tirzepatide.

Compare the mass printed on a certificate with the values above. The mass checker explains charge states and which mass a lab usually reports.

What usually goes wrong with tirzepatide. Documented failure modes, with sources.

A different GLP-1 class peptide under a tirzepatide label

The US FDA warns that illegally marketed semaglutide and tirzepatide could contain the wrong ingredients, and it has warned companies selling tirzepatide falsely labelled "for research purposes" (FDA, unapproved GLP-1 drugs). In a 2026 analysis of compounded semaglutide products, one sample contained a component whose mass corresponded to tirzepatide (Kopp et al., Pharmaceutical Research, 2026). A wrong relative can still give one tidy HPLC peak; only the mass separates them, because tirzepatide (C225H348N48O68) and semaglutide (C187H291N45O59) have very different formulas (PubChem, tirzepatide).

Chains missing or gaining one residue

Tirzepatide for its discovery work was made by conventional peptide chemistry (Coskun et al., Molecular Metabolism, 2018). Solid-phase synthesis produces deletion sequences when Fmoc removal is incomplete, insertion sequences from excess amino acid reagent, and diastereomers when a residue racemises (D'Hondt et al., Journal of Pharmaceutical and Biomedical Analysis, 2014). In follow-on and compounded semaglutide and liraglutide, LC-MS found amino acid deletions and additions absent from the originators (Kopp et al., 2026). A des-residue variant is lighter than the parent by one amino acid, which mass spectrometry reads directly.

Oxidation at tryptophan 25 and deamidation at glutamine

Tirzepatide has one tryptophan (position 25), glutamine at positions 19 and 24, and no methionine, cysteine or asparagine (KEGG D11360). Methionine is the residue most susceptible to oxidation and tryptophan follows it; deamidation mainly affects asparagine and, to a lesser extent, glutamine, and shifts the mass by +0.984 Da (Butré et al., Molecules, 2023). So an oxidised tirzepatide peak points mainly at Trp25, and a deamidated variant, under one mass unit from the parent, needs high-resolution MS or a chromatographic separation to be seen.

Average and monoisotopic mass confused on a certificate

The FDA label states a molecular weight of 4813.53 Da (Mounjaro prescribing information); the discovery paper states 4810.52 Da (Coskun et al., 2018), which matches the monoisotopic mass PubChem calculates. Both are correct: one averages in the heavier natural isotopes, the other uses only the lightest. A report that compares a monoisotopic measurement against the average value creates a three-unit mismatch and can pass or fail a sample for the wrong reason.

Counter-ions and water counted as peptide

Synthetic peptides are cleaved and purified with trifluoroacetic acid and usually leave as trifluoroacetate salts; in one 2025 study trifluoroacetate reached up to 35% of the total weight of the peptide salts tested (Erckes et al., Pharmaceuticals, 2025). Any salt and residual water sit in the weighed powder, so a label amount based on gross powder weight overstates the peptide in the vial.

What we check in Tirzepatide. Silent, with captions.

Which tests matter most

LC-MSConfirms the intact mass of 4813.53 (average) or 4810.52 (monoisotopic) and tells tirzepatide apart from semaglutide or retatrutide, which a purity number cannot do.
HPLC-UVReports the main-peak share and shows deletion, insertion or oxidised variants as extra peaks that LC-MS can then name.
HRMSResolves the isotope pattern, so a deamidated variant (+0.984 Da) or an average versus monoisotopic mix-up can be settled.
Counter-ion contentMeasures trifluoroacetate or acetate so the amount can be stated as peptide, not salt plus peptide.
LAL endotoxinEndotoxin is a bacterial contaminant that none of the chemical tests above detect.

Reading tirzepatide results

On a certificate, look beside the identity line for the expected mass, the measured mass, and whether each is average or monoisotopic. Electrospray gives a ladder of charge states that software deconvolutes into one mass; a value close to 4813.5 against an average reference, or 4810.5 against a monoisotopic one, is consistent with tirzepatide. The mass checker computes both from a sequence.

The approved product is not a powder: the FDA label describes Mounjaro as a clear, colourless to slightly yellow sterile solution in pens and vials (Mounjaro prescribing information). A lyophilised vial's label figure is therefore a claim from whoever filled it, and only an amount test against a characterised reference standard checks it. The amount testing lesson explains how.

Public Tested.ph results

No public tirzepatide records yet

Each public tirzepatide record will appear here with its identity, HPLC purity and measured amount against the label, once the first vial is tested.

FIG 13Amount against the label

Questions about testing tirzepatide

How do I know if my tirzepatide is real?: Test a sample from your own vial or batch. Mass spectrometry should show a mass matching tirzepatide, 4813.53 average or 4810.52 monoisotopic. HPLC then shows how much of the material is that molecule, and an amount test compares the milligrams present with the label. Packaging, powder colour and a seller's certificate cannot tell you which peptide is inside or how much.
What mass should a tirzepatide COA show?: 4813.53 g/mol average, the figure in the FDA label, or 4810.52 Da monoisotopic, the figure PubChem calculates and the 2018 discovery paper quotes. Both are right; the report should say which one it compared against and print the measured value beside it. A measured value far from both points to a different or modified molecule, and should be questioned before any purity figure is accepted.
Can a high HPLC purity prove my vial is tirzepatide?: No. HPLC purity is the share of the main peak among the peaks the method detects. A vial of clean semaglutide or retatrutide labelled as tirzepatide would also give one tall peak and a high percentage. Only a mass measurement says which molecule made that peak, so read purity after identity, and treat a purity figure with no identity result as incomplete.
Does a tirzepatide certificate from the seller count as proof?: It counts as a claim to check. Confirm the certificate names the same batch as your vial, names the laboratory and the analysis date, and can be verified with the issuer. Even a genuine certificate describes the sample that laboratory received, which may not be your vial. Our COA checker walks through each line, and a third-party lab test on your own sample settles it.

Sources

Mounjaro (tirzepatide) prescribing information, Eli Lilly and Company
Coskun T et al. LY3298176, a novel dual GIP and GLP-1 receptor agonist. Mol Metab. 2018;18:3-14, Molecular Metabolism (PMC)
FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss, US Food and Drug Administration
Kopp KL et al. Impurities and Potential Immunogenicity Associated With Follow-on and Compounded GLP-1 Receptor Agonists. Pharm Res. 2026;43(8):2861-2886, Pharmaceutical Research (PMC)
D'Hondt M et al. Related impurities in peptide medicines. J Pharm Biomed Anal. 2014;101:2-30, PubMed
Butré CI et al. Interlaboratory Evaluation of a User-Friendly Benchtop Mass Spectrometer for Multiple-Attribute Monitoring. Molecules. 2023;28(6):2855, Molecules (PMC)
Erckes V et al. Towards a Consensus for the Analysis and Exchange of TFA as a Counterion in Synthetic Peptides. Pharmaceuticals. 2025;18(8):1163, Pharmaceuticals (PMC)
KEGG DRUG D11360, Tirzepatide, Kanehisa Laboratories

Last reviewed 6 Oct 2026.