Ipamorelin vs Sermorelin
Quick Answer
Ipamorelin and sermorelin both increase growth hormone secretion from pituitary somatotrophs, but through different receptors. Ipamorelin is a 5-amino-acid pentapeptide that agonises GHSR-1a, the ghrelin receptor. Sermorelin is a 29-amino-acid analog corresponding to GHRH(1-29) that acts at the GHRH receptor. They are not substitutes for one another — they are two convergent pathways onto the same cell, which is why combination designs are more common than head-to-head ones. Both supplied at ≥99% HPLC-verified purity for in-vitro laboratory research only.
Ipamorelin vs Sermorelin: At a Glance
| Attribute | Ipamorelin | Sermorelin |
|---|---|---|
| Classification | GHRP — growth hormone releasing peptide | GHRH analog |
| Receptor target | GHSR-1a (ghrelin receptor) | GHRH-R (growth hormone-releasing hormone receptor) |
| Amino acid count | 5 (pentapeptide) | 29 |
| Sequence / structure | Aib-His-D-2-Nal-D-Phe-Lys-NH2 | GRF (1-29) NH2 |
| CAS number | 170851-70-4 | 86168-78-7 |
| Molecular weight | 711.85 Da | ~3,357.9 Da |
| Signalling cascade | Calcium-mediated, cAMP-independent | cAMP-PKA cascade |
| Cortisol / prolactin stimulation | Minimal at research concentrations — the defining selectivity | Minimal |
| Non-natural residues | Yes — Aib, D-2-Nal, D-Phe confer protease resistance | No — native GHRH fragment |
| Commonly combined with | CJC-1295 No DAC (GHRH arm) | Ghrelin-receptor agonists (GHSR arm) |
| Purity (Peptide.Express) | ≥99% HPLC verified | ≥99% HPLC verified |
How Ipamorelin and Sermorelin Differ in Research
The most common mistake in comparing these two is treating them as alternatives. They act on different receptors on the same cell, and the physiological response to activating both simultaneously exceeds what either produces alone. In practice that means most research designs featuring one of them feature something from the other class as well.
Ipamorelin is the more chemically unusual of the two. At 711.85 Da it is tiny for a receptor-active peptide, and three of its five residues are non-natural: alpha-aminoisobutyric acid, D-2-naphthylalanine and D-phenylalanine. Those substitutions do two jobs — they resist proteolytic degradation, and they confer the receptor selectivity that separates ipamorelin from earlier GHRPs. GHRP-2 and GHRP-6 stimulate cortisol and prolactin alongside growth hormone; ipamorelin largely does not, which makes it a cleaner tool when cortisol is a confounder in the experimental design.
Sermorelin is the more conventional molecule: the N-terminal 29 residues of endogenous GHRH, unmodified. The C-terminal 15 residues of the full 44-amino-acid hormone turn out to be unnecessary for receptor binding, which is why the truncated fragment retains full activity. Being unmodified is also its limitation — sermorelin has a short plasma half-life relative to stabilised GHRH analogs like tesamorelin, which carry N-terminal modifications specifically to slow degradation.
The evidence bases are asymmetric in an awkward way. Sermorelin has an FDA approval history (as Geref, since withdrawn from market — generally described as a commercial rather than a safety decision) but most of its literature predates 2000. Ipamorelin has cleaner selectivity data but a narrower body of work, and its selectivity window was characterised in a limited preclinical dose range rather than established across conditions. Neither has a modern head-to-head trial against the other.
Frequently Asked Questions
What is the difference between ipamorelin and sermorelin?
The receptor. Ipamorelin is a 5-amino-acid pentapeptide agonising GHSR-1a, the ghrelin receptor, through a calcium-mediated pathway. Sermorelin is a 29-amino-acid GHRH(1-29) analog acting at the GHRH receptor through the cAMP-PKA cascade. Both increase GH secretion; they arrive by different routes.
Is ipamorelin a GHRH analog?
No. Ipamorelin is a GHRP — a growth hormone releasing peptide that mimics ghrelin. Sermorelin, CJC-1295 and tesamorelin are the GHRH analogs.
Why is ipamorelin described as selective?
Because unlike earlier GHRPs such as GHRP-2 and GHRP-6, it produces minimal cortisol and prolactin release at research concentrations. That selectivity comes from the non-natural residues in its sequence, and it matters in any design where cortisol would confound the readout. It is concentration-dependent rather than absolute.
Can ipamorelin and sermorelin be studied together?
They can, and the rationale is the same as for the more common CJC-1295 plus ipamorelin pairing — two convergent pathways onto the same somatotroph. In practice CJC-1295 (No DAC) is used more often than sermorelin for the GHRH arm because of its improved stability.
Which has the longer half-life?
Ipamorelin. Sermorelin is an unmodified native GHRH fragment and is cleared quickly; ipamorelin's non-natural residues resist proteolysis. Published half-life figures for both vary by measurement method, so exact numbers should be taken from the specific study being referenced rather than from a supplier page.
Is sermorelin the same as Geref?
Geref was the brand name under which sermorelin held FDA approval. That approval has since been withdrawn from market, generally described as a commercial rather than a safety decision. Research-market sermorelin is not the approved pharmaceutical product.
What is the difference between sermorelin and tesamorelin?
Length and stability. Sermorelin is the unmodified 29-residue GHRH fragment. Tesamorelin is the full 44-residue GHRH sequence with a trans-3-hexenoic acid modification at the N-terminus that slows metabolic degradation. Tesamorelin also holds a current FDA approval; sermorelin does not.
Are both available at the same purity?
Yes. Both are verified at ≥99% purity by reverse-phase HPLC with LC-MS/MS identity confirmation, and ship with a batch-specific Certificate of Analysis. For in-vitro laboratory research use only.