What a Growth Hormone Secretagogue Is

Secretagogue is a clumsy word doing a simple job. It means a substance that causes something else to be secreted. A growth hormone secretagogue is therefore not growth hormone. It is a compound that asks your own pituitary gland to release more of the growth hormone it already makes. That single distinction is what separates this whole family from growth hormone itself, and it is why so many different-looking names keep landing in the same conversation: MK-677, ipamorelin, CJC-1295, sermorelin, tesamorelin, hexarelin and the GHRPs. They are different keys aimed at the same result, and they fit two different locks.

Two receptors, not one

The family splits at the receptor, and every argument you will read about these compounds sits on one side of that split or the other. The first lock is the growth hormone releasing hormone receptor, the one the body's own hypothalamic signal uses. Sermorelin, CJC-1295 and tesamorelin are analogues of that natural signal, which is why the literature usually calls them GHRH analogues rather than secretagogues in the strict sense. The second lock was found the other way round. In 1996 a team at Merck reported cloning a receptor in the pituitary and hypothalamus that turned out to be the target of a group of small synthetic molecules already known to stimulate and amplify pulsatile growth hormone release, and the authors noted that those compounds appeared to mimic a hormone nobody had identified yet. Three years later the missing hormone turned up in rat stomach, a 28-amino-acid peptide the discoverers named ghrelin. Everything commonly sold as a growth hormone secretagogue acts at that second receptor: the GHRPs including GHRP-2, GHRP-6 and hexarelin, the more selective pentapeptide ipamorelin, and MK-677, which is not a peptide at all but an orally active small molecule.^{[1, 2, 3]}

Why the two families get stacked together

Because they work through separate receptors, the two families add up rather than compete for the same site. A 1998 review of orally active growth hormone secretagogues in Annals of Medicine puts it plainly: these compounds have no structural homology with growth hormone releasing hormone, they act via their own receptor, and their effect on growth hormone release is synergistic with that of GHRH. That one sentence is the entire pharmacological rationale behind the stacks sold as a pair, a GHRH analogue alongside a ghrelin-receptor compound. The same review is worth reading for its ceiling as much as its promise. It reports that the effect of these compounds is partially desensitised, while prolonged intermittent oral use did raise insulin-like growth factor 1 levels, and it closes on the careful note that such treatment could be clinically useful rather than that it is.^[4]

Within each family the members are not interchangeable

The differences inside each lock are the reason all the head-to-head comparisons exist. Ipamorelin was introduced in 1998 as the first selective growth hormone secretagogue, and selectivity is the whole point of it. In swine, both GHRP-6 and GHRP-2 raised ACTH and cortisol, while ipamorelin did not raise either at levels significantly different from those seen after GHRH stimulation, and that held even at exposures far above what it took to release growth hormone. On the GHRH side, CJC-1295 was engineered for duration rather than selectivity. A 2006 study in healthy adults reported an estimated half-life of 5.8 to 8.1 days, with mean plasma growth hormone raised two to ten-fold for six days or more and IGF-1 raised for nine to eleven days after a single injection. Those are pharmacokinetics: measurements of how long a compound and its hormone signal hang around. They are not outcomes.^{[3, 5]}

One outcome, and what it does not automatically buy

All of this converges on one measurable result: more growth hormone released, and downstream of that, more IGF-1. The longest human test of whether that translates into something a person would notice is a two-year, double-blind, randomised, placebo-controlled trial of the oral ghrelin mimetic MK-677 in 65 healthy adults aged 60 to 81, published in Annals of Internal Medicine in 2008. At the hormone level it did exactly what it was meant to: growth hormone and IGF-1 rose into the range seen in healthy young adults. Fat-free mass rose too, while the placebo group's fell. Then comes the finding that gets quoted least often: the increased fat-free mass did not result in changes in strength or function. The investigators also record the rest of the picture. Fasting blood glucose rose and insulin sensitivity fell. Body weight rose by more than fat-free mass did, and the extra fat showed up in the limbs. Cortisol rose. The most frequent side effects were an increase in appetite that settled after a few months, transient mild swelling of the lower legs, and muscle pain. Changes in bone mineral density consistent with increased bone remodelling appeared as well. The authors flag that the trial was not powered to evaluate functional endpoints, which is the honest summary. The hormone reading moved and the body composition reading moved. Whether anything a person would actually feel moved with them was left open.^[6]

What thirty years of this class actually produced

Three decades of work on these receptors has produced a small number of real medicines, and none of them is what the online market is selling. Tesamorelin, a GHRH analogue, is the clearest case. A 2007 trial in the New England Journal of Medicine randomly assigned 412 people with HIV and abdominal fat accumulation to a daily injection of tesamorelin or placebo for 26 weeks, and reported visceral adipose tissue down 15.2 percent against a 5.0 percent rise on placebo, with IGF-1 up 81.0 percent. It reached the market as the prescription medicine Egrifta, made by Theratechnologies and first listed in 2010, for that specific population. Macimorelin, a compound acting at the ghrelin receptor, went a narrower route still. A 2018 multicentre study in the Journal of Clinical Endocrinology and Metabolism tested it as an oral diagnostic against the insulin tolerance test in adults being assessed for growth hormone deficiency, and reported 87 percent sensitivity and 96 percent specificity at the prespecified thresholds. That is a diagnostic test, not a therapy. MK-677 has been studied in people for decades and is still not a medicine anywhere. These compounds are not approved by the FDA for raising growth hormone in an otherwise healthy adult, and what is sold online for that purpose is research chemical stock.^{[7, 8, 10]}

Prohibited in sport, named individually

If you are tested in any sport under the World Anti-Doping Code, this entire family is out, and the Prohibited List does not leave it to interpretation. On the 2026 list, in force from 1 January 2026, section S2.2.4 covers growth hormone releasing factors and names three groups. Growth hormone releasing hormone and its analogues, with CJC-1293, CJC-1295, sermorelin and tesamorelin given as examples. Growth hormone secretagogues and their mimetics, with anamorelin, capromorelin, ibutamoren (which is MK-677), ipamorelin, lenomorelin (which is ghrelin), macimorelin and tabimorelin. And GH-releasing peptides, with alexamorelin, examorelin (better known as hexarelin), and GHRP-1 through GHRP-6. Section S2 is prohibited at all times, in and out of competition. That is a year-round prohibition, with no threshold below which the rule stops applying.^[9]

Where the individual arguments get settled

This page is the shared foundation. The choices between individual compounds get decided one pairing at a time, and we keep each of those separate rather than blurring them into a single verdict. The two most-searched pairings are CJC-1295 vs ipamorelin, which is a GHRH analogue against a ghrelin-receptor compound, and ipamorelin vs sermorelin, which is the same split seen from the other side. MK-677 vs ipamorelin is the oral small molecule against the injectable peptide. GHRP-2 vs GHRP-6 vs ipamorelin is the within-family comparison, which is where the cortisol and appetite differences matter most, and CJC-1295 and ipamorelin covers the stack itself. The individual compound sheets are MK-677, ipamorelin, CJC-1295, sermorelin, tesamorelin, hexarelin, GHRP-2 and GHRP-6, and our longest evidence write-up in the family is the MK-677 verdict. If the question underneath yours is really about growth hormone itself rather than the compounds that release it, that comparison lives at peptides vs HGH injections.

References & sources

1. Howard AD, Feighner SD, Cully DF, et al. A receptor in pituitary and hypothalamus that functions in growth hormone release. Science 1996;273(5277):974-977.
2. Kojima M, Hosoda H, Date Y, Nakazato M, Matsuo H, Kangawa K. Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature 1999;402(6762):656-660.
3. Raun K, Hansen BS, Johansen NL, et al. Ipamorelin, the first selective growth hormone secretagogue. European Journal of Endocrinology 1998;139(5):552-561.
4. Ghigo E, Arvat E, Camanni F. Orally active growth hormone secretagogues: state of the art and clinical perspectives. Annals of Medicine 1998;30(2):159-168.
5. Teichman SL, Neale A, Lawrence B, Gagnon C, Castaigne JP, Frohman LA. Prolonged stimulation of growth hormone and insulin-like growth factor I secretion by CJC-1295, a long-acting analog of GH-releasing hormone, in healthy adults. Journal of Clinical Endocrinology and Metabolism 2006;91(3):799-805.
6. Nass R, Pezzoli SS, Oliveri MC, et al. Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Annals of Internal Medicine 2008;149(9):601-611.
7. Falutz J, Allas S, Blot K, et al. Metabolic effects of a growth hormone-releasing factor in patients with HIV. New England Journal of Medicine 2007;357(23):2359-2370.
8. Garcia JM, Biller BMK, Korbonits M, et al. Macimorelin as a Diagnostic Test for Adult GH Deficiency. Journal of Clinical Endocrinology and Metabolism 2018;103(8):3083-3093.
9. World Anti-Doping Agency, The 2026 Prohibited List, in force 1 January 2026 (section S2.2.4, growth hormone releasing factors).
10. U.S. Food and Drug Administration, Drugs@FDA record for EGRIFTA (tesamorelin acetate), BLA 022505, Theratechnologies, marketing status Prescription, original action date 10 November 2010.