What is Tesamorelin + Ipamorelin?
Tesamorelin is a growth-hormone-releasing factor analogue, CAS 218949-48-5, formula C221H366N72O67S, molecular weight 5135.9, built on the GRF(1-44) scaffold. Ipamorelin is a growth-hormone secretagogue, CAS 170851-70-4, formula C38H49N9O5, molecular weight 711.85, sequence H-Aib-His-D-2-Nal-D-Phe-Lys-NH2. That sequence carries three non-standard features, an alpha-aminoisobutyric acid at the N-terminus, two D-configured aromatic residues, and a C-terminal amide, all of which slow enzymatic breakdown relative to an all-L linear peptide.
The pairing follows a logic well described in endocrine pharmacology. GHRH analogues engage the GHRH receptor on somatotroph cells, while secretagogues of the ipamorelin type act at the growth hormone secretagogue receptor through a separate signaling route. In rodent and cell studies the two classes produce responses described as additive rather than redundant, and ipamorelin is characterized as comparatively selective relative to earlier secretagogues.
What is not settled is how this fixed ratio compares with the two peptides assayed separately, since no controlled study of the co-lyophilized preparation has been published. The relative contribution of each receptor pathway also varies between species and model systems, so results do not transfer cleanly between preparations.
Reconstitution & handling
Bacteriostatic or sterile water added slowly against the vial wall dissolves both components, and the cake should clear within a minute of gentle swirling. Total concentration is the labeled 15 mg divided by the diluent volume, with individual concentrations following the 10 to 5 split. The larger tesamorelin chain foams if the vial is shaken, so letting it stand is preferable. Visible haze means the vial should not be used analytically.
Storage & stability
Lyophilized vials are held at -20 degrees Celsius, protected from light and from moisture, with the cake dry and intact. After reconstitution the solution is refrigerated at 2 to 8 degrees Celsius, divided into single-use aliquots, and kept clear of repeated freeze-thaw cycles, the main practical cause of potency loss in solution. Tesamorelin is the larger and more conformationally complex component and is therefore the fraction most sensitive to thermal excursions.
How it's tested
Reverse-phase HPLC with detection at 214 and 220 nanometres separates the two components cleanly given the large mass difference, and relative peak areas are compared against the declared 10 to 5 ratio. Mass spectrometry confirms identity against theoretical average masses of 5135.9 and 711.85, with the non-standard residues of ipamorelin giving a distinctive fragmentation pattern. Net peptide content is measured so the 15 mg label reflects peptide alone.