Secretagogue means a substance that causes something else to be secreted. In this group the something else is endogenous growth hormone, and the compounds are grouped by that shared downstream effect rather than by any shared structure.
That grouping is why the category is confusing: it contains two chemically unrelated families that reach the same axis by different routes.
Family one: GHRH analogues
Growth hormone releasing hormone is a hypothalamic peptide acting on the GHRH receptor in the pituitary. Analogues in this family are modified versions of that sequence, usually truncated to the first 29 residues, which retains receptor activity.
- Sermorelin corresponds to that 1-29 fragment.
- CJC-1295 adds substitutions that resist DPP-4 cleavage, the same enzyme that constrains the incretin class.
- Tesamorelin is a GHRH analogue carrying an N-terminal modification.
What DAC means
CJC-1295 appears in catalogs in two forms, with DAC and without, and the distinction is frequently misunderstood. DAC stands for Drug Affinity Complex: a maleimide group that forms a covalent bond with circulating albumin, greatly extending the molecule's residence time.
CJC-1295 without DAC is, structurally, the modified 1-29 fragment on its own and is often listed under the name modified GRF (1-29). The two forms have different molecular weights and are not interchangeable. A certificate's observed mass distinguishes them unambiguously.
Family two: ghrelin receptor agonists
The second family acts on the growth hormone secretagogue receptor, the target of the hormone ghrelin, which is a different receptor from GHRH's. These are structurally unrelated to the GHRH analogues.
- Ipamorelin is a pentapeptide, notable in the literature for receptor selectivity relative to earlier compounds in the family.
- GHRP-2 and GHRP-6 are earlier hexapeptides in the same family.
- Hexarelin is a related hexapeptide.
Note that despite the shared GHRP naming, these are short synthetic sequences rather than fragments of a natural hormone.
Why the two families are studied together
Because they act at separate receptors on the same axis, combinations of one from each family are common in published work and in catalog blends. CJC-1295 with ipamorelin is the most frequently listed pairing.
For a buyer the relevant consequence is documentary. A blend raises questions a single vial does not: what the ratio is, whether purity was determined for each component or only for the mixture, and what the stated total mass refers to.
A note on HGH fragment 176-191
This compound is frequently filed in the same category and does not belong to either family. It is a fragment of the growth hormone molecule itself rather than something that causes growth hormone to be released, so it is not a secretagogue at all. Catalog adjacency is not mechanism.
What to check
- Observed mass, which separates CJC-1295 with DAC from the version without it.
- Which family a compound belongs to, if the pairing in a blend is the point.
- For blends, per-component purity rather than a single mixture figure.
- Net peptide content, as always, for the counterion and moisture gap.
All compounds here are supplied strictly for laboratory research.
Receptor class explains what separates these compounds pharmacologically. It says nothing about what is in a given vial, which is settled by mass spectrometry and peptide identity and by the content line discussed in net peptide content.
Two receptor routes, and why the distinction is practical
The compounds in this group act through different receptors, and that difference is structural rather than a matter of degree. Reading which route a compound uses is the fastest way to understand why two products in the same category behave differently in published work.
For purchasing, the consequence is narrow but real: compounds acting through different receptors are not interchangeable, and a supplier substituting one for another because of stock is making a change that matters.
What varies across the group at the bench
Chain length, modifications and salt form all vary within this category, and each changes handling. A short unmodified peptide and an acylated longer one have different solubility behaviour and different storage sensitivities, despite sitting under one heading.
Why some peptides resist dissolving covers the solubility side. The general rule is to read handling from the sequence rather than from the category name.
What a certificate establishes for this group
Identity, purity and content, on the same terms as any other peptide of comparable length. Nothing on a certificate speaks to receptor activity, and no supplier can supply a document that does, because activity is measured in an assay rather than reported on a release panel.
That boundary is worth holding onto, because this is a category where marketing language reaches toward function. A complete certificate tells you what is in the vial and how much of it there is. What the compound does in a given system is established by the literature and by your own work, not by the paperwork accompanying the order.
Practical differences that affect ordering
Members of this group differ in how readily they dissolve, how they tolerate storage in solution, and how much their mass shifts with modification. An acylated compound and a short unmodified one are not comparable on any of those axes despite appearing under one heading.
Order and document them separately, size vials against actual consumption rather than category convenience, and read handling from each sequence. Building a research peptide formulary covers deciding which members of a class are worth stocking at all.
One closing point about substitution. Where a supplier offers an alternative from the same category because of stock, treat that as a change of compound rather than a change of brand, and re-check the sequence, mass and certificate as you would for any new material.
For where this sits among the other molecules a catalogue carries, not everything in a peptide catalog is a peptide covers how the classes differ.