Sermorelin: GHRH(1-29) and the Reference Analog
Sermorelin is the shortest fragment of growth hormone-releasing hormone that retains full receptor activity, and it is essentially unmodified. That combination makes it the reference compound in its family: every engineered GHRH analog is, in effect, an answer to a problem that sermorelin has and does not solve.
The sequence
Native GHRH is 44 residues. Sermorelin corresponds to the first 29 of them, carried as a C-terminal amide — GHRH(1-29)-NH2. Residues 30 to 44 contribute nothing to receptor activation, which is why truncation at 29 is the standard economy and why several analogs are built on the same fragment.
What distinguishes sermorelin from those analogs is what has not been done to it. There is no acylation, no substituted residue, no albumin-binding group. It is the parent pharmacophore with the redundant tail removed, and nothing else.
Where it is cleaved, and why that matters
The N-terminus of GHRH begins Tyr-Ala, and dipeptidyl peptidase-4 removes N-terminal dipeptides where the second residue is alanine or proline. GHRH(1-29) presents exactly that motif, so DPP-4 cleaves between Ala2 and Asp3, and the resulting GHRH(3-29) has lost the receptor-binding determinants at the N-terminus.
This single vulnerability explains the entire design space around the molecule. Tesamorelin attaches a trans-3-hexenoyl group at the N-terminus so the protease has nothing to grip. CJC-1295 substitutes residues in the cleavage region and, in its DAC form, adds a group that binds serum albumin — see the difference between the DAC and no-DAC forms. Each is a different answer to the same question, and sermorelin is the unanswered version.
The consequence for anyone working with it is straightforward: in any preparation containing DPP-4 activity, sermorelin is being consumed while the experiment runs. That is a property of the molecule rather than a defect in the material, and no certificate of analysis will tell you about it.
The C-terminal amide is not optional
Amidation of the C-terminus is required for full activity at the GHRH receptor. The corresponding free acid, which is what results if the amide is absent or lost, is substantially less potent.
It is also nearly invisible. The amide and the free acid differ by about one dalton, they behave almost identically on a reversed-phase column, and they look the same in the vial. A mass spectrum will separate them, but only if the question is asked deliberately — when reading a certificate, check that the calculated mass quoted is for the amidated form. Our guide to reading a certificate of analysis covers the fields, and how purity and identity are verified explains what each method can and cannot resolve.
Receptor coupling, and choosing the right readout
The GHRH receptor is a class B G protein-coupled receptor, in the same structural family as the receptors for secretin, glucagon and the incretins. It couples to Gαs, which activates adenylate cyclase and raises intracellular cAMP.
That matters for assay selection, and it is where designs most often go wrong by analogy. A cAMP accumulation assay is the correct default here. Calcium flux, which is the right instrument for a Gαq-coupled receptor such as KISS1R — see kisspeptin-10 and KISS1R signalling — is the wrong one for GHRHR, and a weak or absent calcium response says nothing about whether the compound is active.
The indexed literature is at PubMed, alongside the broader GHRH receptor structure-activity literature.
When the reference compound is the right choice
Because sermorelin is short-lived, it is easy to treat as the inferior member of the family. That framing is wrong often enough to be worth correcting.
GHRH receptor signalling is pulsatile, and a stabilised analog with an extended exposure profile is not a longer-lasting version of the native signal — it is a different signal, and receptors that desensitise under sustained stimulation will behave accordingly. Where the question concerns transient, native-like receptor engagement, the unmodified fragment is the more faithful tool and a long-acting analog is the confound.
The corollary is the design error the whole family invites: treating GHRH analogs as interchangeable. A protocol written around sermorelin does not transfer to tesamorelin or to CJC-1295 with DAC, and results obtained with one should not be pooled with the other. Our comparison of GHRH analogs against growth hormone secretagogues sets out how the two mechanisms differ, and peptide half-life and how analogs extend it covers the chemistry of the modifications themselves.
Handling
Sermorelin ships as a lyophilised powder and is stable in that form when kept sealed, cold and dry. The practical risks are the ordinary ones for a peptide of this length, and two are worth naming.
The first is moisture. Let a vial reach room temperature before breaking the seal; opening a cold vial in a warm room condenses water directly onto the cake, and water is what drives hydrolysis and the deamidation of asparagine and glutamine residues during storage. See storage and stability.
The second is the solution, not the powder. A 29-residue peptide with real helical propensity aggregates more readily than a short linear one, and repeated freeze-thaw cycling accelerates it through the ice interface rather than through heat. Reconstitute once, split into single-use volumes before freezing, and every later thaw is the first thaw for that aliquot — see aliquoting reconstituted peptides.
As with any synthetic peptide, the milligram figure on the vial is gross weight. Counter-ions and residual water are part of that mass and not part of the peptide, so molarity calculated from the label is overstated — see net peptide content explained.
Products
Sermorelin 5mg and Sermorelin 10mg, listed with other growth hormone pathway compounds. Certificates of analysis for every batch are published on the certificates page.
ExoLabz supplies compounds for laboratory research use only. Nothing on this page is medical advice or a suggestion of human or veterinary use. These compounds hold no Canadian market authorisation for human use.
