One of the 30 compound testing profiles
Liraglutide
Liraglutide is a 31-amino-acid peptide (C172H265N43O51, average mass 3751.2 g/mol) with a C16 palmitic acid attached to lysine 26 through a glutamic acid spacer; a test should confirm that mass and, because its backbone is nearly identical to semaglutide's, make sure the vial is not the other molecule.
Liraglutide is an analogue of human GLP-1 that acts as a GLP-1 receptor agonist, and it is the active ingredient of Victoza, a prescription medicine approved by the US FDA (Victoza prescribing information, section 11).
Identity card
- Formula
- C172H265N43O51
- Average mass
- 3,751.2 g/mol
- Monoisotopic mass
- 3,748.95 Da
- Length
- 31 residues
- Modifications
- Lys26 in GLP-1 numbering (position 20 here) carries palmitic acid (C16) through a glutamic acid spacer; Arg at position 34 in GLP-1 numbering (position 28 here) in place of lysine; Free C-terminal acid
- Also sold as
- Lira, NN2211
- Sequence
- HAEGTFTSDVSSYLEGQAAKEFIAWLVRGRG
- Note
- The FDA label gives the formula and a molecular weight of 3751.2 Daltons. PubChem rounds the average mass to 3751 and gives a monoisotopic mass of 3748.9464612 Da, recorded as 3748.95. The sequence is taken from PubChem's condensed IUPAC notation, H-His-Ala-Glu-...-Arg-Gly-OH with palmitoyl-Glu on Lys20. Residues are usually numbered 7 to 37 after native GLP-1.
Source: PubChem CID 16134956, Liraglutide, Victoza (liraglutide) prescribing information, section 11 Description.
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 liraglutide. Documented failure modes, with sources.
Recombinant originator, copies made another way
The originator's peptide precursor is expressed from recombinant DNA in Saccharomyces cerevisiae, and the palmitic acid and spacer are attached afterwards (Victoza prescribing information). A 2026 study by Novo Nordisk scientists found that follow-on and compounded liraglutide and semaglutide products had impurity profiles unlike the originators, including amino acid deletions, additions and unidentified impurities, and linked the differences to API sourcing, manufacturing process and degradation in storage (Kopp et al., Pharmaceutical Research, 2026). A high main-peak purity does not say which impurities make up the rest.
Faster fibril formation
In the same study, two generic liraglutide products approved in South America reached fibrillation sooner than the originator in a thioflavin T stress assay, which the authors read as impaired physical stability (Kopp et al., 2026). Aggregated material may not be fully recovered in the solution that is analysed, so it reads as a low amount. A report should note whether the sample dissolved clear; covalent dimers and trimers show in LC-MS as high-mass species.
Semaglutide differs by one backbone residue
The two sequence strings differ only at position 2: alanine in liraglutide (PubChem), Aib in semaglutide (KEGG D10025). The side chains differ more: palmitic acid (C16) on a glutamic acid spacer for liraglutide, a C18 fatty diacid on a hydrophilic spacer for semaglutide (Ozempic prescribing information). Backbone fragments in a peptide map can therefore look alike, but the intact masses do not: 3751.2 for liraglutide against 4113.58 for semaglutide. Intact-mass LC-MS is the clean way to tell them apart.
His7 racemisation and Trp31 oxidation
Liraglutide begins with histidine, historically a notoriously racemisation-prone residue during peptide coupling, and the D-His form weighs the same as the target, so only chromatography shows it (Behrendt et al., Journal of Peptide Science, 2016). It has no methionine, the residue most susceptible to oxidation, so its single tryptophan (position 31 in GLP-1 numbering), the next most susceptible, is the main oxidation site (Butré et al., Molecules, 2023). Oxidation adds an oxygen atom, which mass spectrometry reads directly.
Transcript
What we check in Liraglutide. Identity by mass. The expected average mass is 3751.2 g/mol. Purity by HPLC: the main peak's share of the peaks the method detects. Amount: the milligrams measured in the vial, against the label. Documented risk: liraglutide and semaglutide share almost the whole backbone. Their intact masses differ, so intact-mass LC-MS tells them apart.
Which tests matter most
- LC-MSConfirms the 3751.2 intact mass, separates liraglutide from semaglutide, and shows dimers, trimers and deletion variants by mass.
- HPLC-UVGives the purity figure and resolves same-mass variants such as a D-histidine form that mass spectrometry alone cannot.
- Peptide mappingPlaces the palmitoyl spacer on Lys26 and the arginine at 34, useful when an intact mass is close but not exact.
- Appearance and solubilityRecords cloudiness or particles, relevant for a peptide whose follow-on versions have fibrillated faster.
Reading liraglutide results
Residue numbering varies: 1 to 31 along the chain, or 7 to 37 after native GLP-1, so the acylated lysine may be called Lys20 or Lys26 and the arginine Arg28 or Arg34. Both are the same molecule. The mass checker works out average and monoisotopic masses from a sequence.
The approved product is a clear, colourless solution in a prefilled pen (Victoza prescribing information). Lyophilised vials are a different presentation, and their label figures are whatever the filler printed. No common label amounts are listed because Tested.ph has not yet recorded liraglutide vial listings. The amount testing lesson explains how measured content is compared with a label.
Public Tested.ph results
No public liraglutide records yet
Each public liraglutide 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 liraglutide
- What mass should a liraglutide COA show?
- The FDA label lists liraglutide as C172H265N43O51 with a molecular weight of 3751.2 Daltons, and PubChem gives a monoisotopic mass of 3748.95 Da. A good certificate prints the expected and the measured value and says which kind of mass it used. A measured mass near 4113.6 points to semaglutide rather than liraglutide, whatever the label says.
- How can I tell liraglutide from semaglutide?
- By intact mass. Their backbones differ at a single position, alanine against Aib, and both carry a fatty side chain on the lysine at GLP-1 position 26. But the whole molecules weigh 3751.2 and 4113.58, a gap any working mass spectrometer resolves. HPLC purity cannot tell them apart, because either would give a single clean peak.
- Are generic or compounded liraglutide products the same as the original?
- They should contain the same active molecule, but published testing shows their impurity profiles can differ. A 2026 study by the originator's manufacturer found follow-on and compounded liraglutide and semaglutide products with deletion, addition and unidentified impurities absent from the originators, and two liraglutide generics fibrillated sooner under stress. Testing a sample shows what a specific product contains.
Sources
- Victoza (liraglutide) prescribing information, Novo Nordisk
- 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)
- PubChem CID 16134956, Liraglutide, National Library of Medicine
- KEGG DRUG D10025, Semaglutide, Kanehisa Laboratories
- Ozempic (semaglutide) prescribing information, Novo Nordisk
- Behrendt R, White P, Offer J. Advances in Fmoc solid-phase peptide synthesis. J Pept Sci. 2016;22(1):4-27, Journal of Peptide Science (PMC)
- Butré CI et al. Interlaboratory Evaluation of a User-Friendly Benchtop Mass Spectrometer. Molecules. 2023;28(6):2855, Molecules (PMC)
Last reviewed 6 Oct 2026.