Here is the thing almost every comparison of these three gets wrong. Two of them are edits of the same 1982 molecule. The third is an impostor that hits a different receptor entirely. Lump all three together as “growth hormone peptides” and you will design a study that can’t tell them apart.
We will sort them by receptor, because that is the line that actually matters. First, though, where the parent molecule came from.
One hormone, two edits, one impostor
Back in 1982, Guillemin’s group pulled a 44-amino-acid peptide out of a human pancreatic tumor sample. The synthetic copy did exactly what the natural hormone did: it triggered growth hormone release in vitro and in vivo, and it matched the hypothalamic growth hormone-releasing factor nobody had characterized yet [1]. That peptide is GHRH, also written GRF. Its sequence opens Tyr-Ala-Asp-Ala-Ile-Phe, and that first tyrosine is the pressure point for everything below.
Sermorelin and tesamorelin are both carved from GHRH. Ipamorelin is not. Keep that split in your head.
Sermorelin: the shortest working fragment
You do not need all 44 residues. The first 29, capped with an amide, keep the activity. That fragment, GRF(1-29)NH2, is sermorelin, and it serves as the native reference peptide in GHRH analogue work [2]. Everything past residue 29 can go, which is why the fragment, not the full peptide, became the yardstick.
Now the weakness. Native GHRH does not last in plasma. Frohman’s lab put human GHRH(1-44) into human plasma in vitro and watched it by HPLC. Half-life: 17 minutes. The main leftover fragment held under 0.1% of the original activity [3]. Sermorelin is an unmodified fragment, so it inherits that same short clock. If your assay runs longer than a few minutes, that instability is not a detail, it is the main thing standing between you and a clean reading.
What chews it up got a name in 1989. Dipeptidylpeptidase IV, DPP-IV, snips off the first two residues, and a D-amino acid at position 1 or 2 stops the snip cold [4]. Remember that, because the next compound was built around exactly this problem.
Tesamorelin: the same backbone, with a guard
Tesamorelin is GHRH with one tweak. Its development name was TH9507, and the change is a trans-3-hexenoyl group bolted onto the tyrosine at position 1. That single addition made it resistant to DPP-IV [5].
The kinetics show the payoff. In the early animal work, the modification slowed degradation in rat, dog and human plasma and stretched elimination in the live animal. In dogs the apparent elimination half-life ran 21 to 45 minutes [5]. Same lock, same key as sermorelin. Tesamorelin just posted a guard at the one spot the enzyme attacks, which is why the two make such a clean matched pair for a stability study: identical backbone, one deliberate difference.
Ipamorelin: a different receptor altogether
Ipamorelin never touches the GHRH receptor. It is a pentapeptide, Aib-His-D-2-Nal-D-Phe-Lys-NH2, and it binds GHS-R1a, the growth hormone secretagogue receptor most people now call the ghrelin receptor [6].
So the comparison is lopsided, and in a useful way. Set sermorelin or tesamorelin next to ipamorelin and you are running two receptor systems, not three flavors of one.
What makes ipamorelin interesting is its selectivity. In Raun’s study it released growth hormone from rat pituitary cells about as well as GHRP-6 (EC50 1.3 versus 2.2 nmol/L). Unlike the older GHRPs, it did not push ACTH or cortisol past what GHRH itself did, even at more than 200 times the level it needed for a half-maximal growth hormone response. “Very surprisingly,” the authors wrote in the abstract [6]. For study design that is gold, since a compound that leaves the stress-hormone axis quiet lets you read a growth hormone signal without cortisol sitting on top of it. The catch: that profile came from swine.
Side by side
| Sermorelin | Tesamorelin | Ipamorelin | |
|---|---|---|---|
| Based on | GHRH(1-29) | GHRH(1-44), modified | None (ghrelin-receptor ligand) |
| Receptor | GHRH receptor | GHRH receptor | GHS-R1a |
| Key design feature | Shortest active GHRH fragment | trans-3-hexenoyl on Tyr1, DPP-IV resistant | Pentapeptide, high GH selectivity |
| Plasma stability note | DPP-IV sensitive, like native GHRH | Half-life 21 to 45 min in dogs [5] | Selective, cortisol-sparing in swine [6] |
How to design the comparison
A few things fall straight out of the biology. Comparing sermorelin against tesamorelin? The real variable is DPP-IV resistance, so the difference lives in a plasma-stability assay, not a single-timepoint snapshot that papers over it. Adding ipamorelin? You have crossed to another receptor, so a GHS-R antagonist control earns its spot on the plate.
And running a GHRH-receptor compound alongside ipamorelin means two receptors fire at once. Build a control arm for each, or the data won’t tell you which one did the work.
For one of these on its own, see our tesamorelin GHRH analogue guide. Our sermorelin vs ipamorelin analysis digs into that two-way split.
References
- Guillemin R, et al. Science. 1982;218(4572):585-587. PubMed 6812220
- Dubreuil P, et al. Growth Horm IGF Res. 2001;11(3):173-186. PubMed 11735232
- Frohman LA, et al. J Clin Invest. 1986;78(4):906-913. PubMed 3093533
- Frohman LA, et al. J Clin Invest. 1989;83(5):1533-1540. PubMed 2565342
- Ferdinandi ES, et al. Basic Clin Pharmacol Toxicol. 2007;100(1):49-58. PubMed 17214611
- Raun K, et al. Eur J Endocrinol. 1998;139(5):552-561. PubMed 9849822
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