GHRH analogs and GHRPs are stacked together for a reason grounded in a real human study: giving both at once produced a GH pulse larger than the two added together. GH area under the curve was 686 for GHRH alone, 1787 for GHRP-6 alone, and 4111 for the pair.
GHRH analogs and GHRPs are the two families of growth hormone peptides, and they differ at the receptor. GHRH analogs, sermorelin, CJC-1295, and tesamorelin, bind the GHRH receptor and increase how much GH the pituitary makes. GHRPs, also called growth hormone secretagogues, bind the ghrelin receptor and increase how much GH the pituitary releases. Both raise GH and IGF-1. They do it through different doors, which is why they are combined rather than swapped.
- GHRH analogs (sermorelin, CJC-1295, tesamorelin) bind the GHRH receptor [1][2]
- GHRPs / secretagogues (ipamorelin, GHRP-6, GHRP-2) bind the ghrelin receptor [3]
- Combined, they are supra-additive: a human study showed a GH response greater than the sum of each alone [4]
- GHRPs can stimulate appetite and, except for ipamorelin, cortisol; GHRH analogs do neither [3]
- Neither class has an FDA-approved anti-aging product; all such use is compounded and off-label [5]
GHRH Analogs: The Production Side
GHRH analogs copy growth hormone-releasing hormone, the hypothalamic signal that tells the pituitary to produce and release GH. Sermorelin is a 29-amino acid analog of GHRH, the shortest fragment with full biological activity [1]. It binds the GHRH receptor and increases GH production while the somatostatin feedback loop stays intact, so the pituitary self-limits and physiologic overshoot is difficult to reach.
The class differs mainly by duration. Sermorelin is short-acting, with a half-life measured in minutes, and adding a D-Ala substitution to the GHRH fragment increases the half-life and decreases metabolic clearance [6]. CJC-1295 extends this much further: it is a long-acting GHRH analog that raised mean GH and IGF-1 for days after a single dose [2]. A study designed to test whether that continuous stimulation flattens the natural rhythm found that GH pulse frequency and magnitude stayed intact while basal GH rose 7.5-fold and IGF-1 rose 45% one week after dosing [7]. Tesamorelin is the GHRH analog with the strongest trial data, studied for visceral fat reduction.
GHRPs: The Release Side
GHRPs, growth hormone-releasing peptides, are growth hormone secretagogues that act on the ghrelin receptor rather than the GHRH receptor. Ipamorelin was introduced as the first selective growth hormone secretagogue [3]. The class also includes GHRP-6 and GHRP-2, the older members.
Selectivity is what separates them inside the class. In the foundational study, ipamorelin released GH without raising cortisol or ACTH even at more than 200 times its GH ED50, while GHRP-6 and GHRP-2 raised both [3]. Because the ghrelin receptor also drives hunger, GHRPs can increase appetite, most noticeably GHRP-6. That is a property GHRH analogs do not share.
Why They Are Stacked
Combining a GHRH analog with a GHRP is the standard peptide stack because the two receptors converge on the same pituitary cells through different pathways, so stimulating both yields more GH than either alone. This is not theory. In normal subjects given GHRH and GHRP-6 separately and together, GH area under the curve was 686 for GHRH alone, 1787 for GHRP-6 alone, and 4111 for the combination, significantly greater than the arithmetic sum [4].
That study used GHRH and GHRP-6, not sermorelin and ipamorelin specifically. The principle that a GHRH analog plus a secretagogue is supra-additive is established in humans. That any particular branded blend reproduces that exact magnitude is an extrapolation, and no trial has tested sermorelin plus ipamorelin directly.
GHRH Analogs vs GHRPs at a Glance
| GHRH analogs | GHRPs / secretagogues | |
|---|---|---|
| Examples | Sermorelin, CJC-1295, tesamorelin | Ipamorelin, GHRP-6, GHRP-2 |
| Receptor | GHRH receptor [1] | Ghrelin receptor (GHS-R1a) [3] |
| Primary effect | Increases GH production | Triggers GH release |
| Appetite | Not stimulated | Can be stimulated, strongest with GHRP-6 |
| Cortisol / ACTH | Not raised | Raised by GHRP-6/GHRP-2; not by ipamorelin [3] |
| Feedback loop | Somatostatin intact | Somatostatin intact |
| FDA-approved anti-aging product | None [5] | None [5] |
| WADA status | Prohibited, S2.2.4 [8] | Prohibited, S2.2.4 [8] |
Which One We Route To
For age-related GH decline with an intact pituitary, a GHRH analog is the first-line choice, and sermorelin is the most established of them for that use. It restores the axis toward normal, keeps the feedback loop in play, and does not add appetite. A selective GHRP, ipamorelin, is the sensible second agent when a stack is warranted, because it adds a release signal without the cortisol rise of the older secretagogues [3].
What neither class is: FDA-approved for anti-aging or body composition. There are no approved products for these uses, so every protocol is compounded and off-label, and ipamorelin specifically appears on FDA’s list of bulk substances that may present significant safety risks [5]. A legitimate program starts with a baseline IGF-1 and monitors it, whichever class it prescribes.
The right peptide depends on your goal and your baseline IGF-1, not on which class a program happens to sell. SystemLabs tests IGF-1 before prescribing and works across GHRH analogs and selective secretagogues, so the choice follows your numbers.
Bottom Line
Frequently Asked Questions
What is the difference between GHRH and GHRP?
They act on different receptors. GHRH analogs bind the GHRH receptor and increase how much growth hormone the pituitary produces [1]. GHRPs, the growth hormone secretagogues, bind the ghrelin receptor and trigger the pituitary to release GH [3]. Both raise GH and IGF-1, but through separate pathways, which is why they are often combined rather than used as substitutes for each other.
Is sermorelin a GHRH or a GHRP?
Sermorelin is a GHRH analog. It is a 29-amino acid analog of growth hormone-releasing hormone and binds the GHRH receptor on the pituitary [1]. It is not a GHRP, so it does not act on the ghrelin receptor and does not carry the appetite-stimulating property of the secretagogue class.
Is ipamorelin a GHRH or a GHRP?
Ipamorelin is a GHRP, a growth hormone-releasing peptide, also called a secretagogue. It binds the ghrelin receptor and was introduced as the first selective secretagogue, meaning it releases GH without the cortisol and ACTH rise of GHRP-6 and GHRP-2 [3]. It is commonly paired with a GHRH analog rather than used alone.
Why are GHRH and GHRP peptides combined?
Because they are supra-additive. The two receptors sit on the same pituitary cells but work through different pathways, so stimulating both releases more GH than either alone. In normal subjects, GH area under the curve was 686 for GHRH alone, 1787 for GHRP-6 alone, and 4111 for the combination, greater than the arithmetic sum [4]. That is the mechanistic basis for the sermorelin-plus-ipamorelin style stack.
Which is better, GHRH or GHRP?
Neither is universally better; they do different jobs. For age-related GH decline with an intact pituitary, a GHRH analog such as sermorelin is the usual first-line choice because it restores the axis toward normal without adding appetite. A selective GHRP such as ipamorelin is the logical second agent when a stack is warranted [3]. The strongest response comes from combining them, not choosing one.
Do GHRH or GHRP peptides raise cortisol?
GHRH analogs do not raise cortisol. Among GHRPs, the older ones, GHRP-6 and GHRP-2, do raise cortisol and ACTH, while ipamorelin does not at levels significantly different from GHRH stimulation even at high multiples of its GH dose [3]. That cortisol selectivity is the main reason ipamorelin is preferred over the older secretagogues.
References
- Sermorelin: a review of its use in the diagnosis and treatment of children with idiopathic growth hormone deficiency BioDrugs, 1999. PMID: 18031173. https://pubmed.ncbi.nlm.nih.gov/18031173/
- Prolonged stimulation of growth hormone (GH) 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 & Metabolism, 2006. PMID: 16352683. https://pubmed.ncbi.nlm.nih.gov/16352683/
- Ipamorelin, the first selective growth hormone secretagogue European Journal of Endocrinology, 1998. PMID: 9849822. https://pubmed.ncbi.nlm.nih.gov/9849822/
- Growth hormone (GH) secretion in active acromegaly after the combined administration of GH-releasing hormone and GH-releasing peptide-6 Journal of Clinical Endocrinology & Metabolism, 1994. PMID: 8045963. https://pubmed.ncbi.nlm.nih.gov/8045963/
- Certain bulk drug substances for use in compounding that may present significant safety risks FDA.gov, Human Drug Compounding, 2026. Content current as of 04/22/2026. https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
- Incorporation of D-Ala2 in growth hormone-releasing hormone-(1-29)-NH2 increases the half-life and decreases metabolic clearance in normal men Journal of Clinical Endocrinology & Metabolism, 1994. PMID: 7962295. https://pubmed.ncbi.nlm.nih.gov/7962295/
- Pulsatile secretion of growth hormone (GH) persists during continuous stimulation by CJC-1295, a long-acting GH-releasing hormone analog Journal of Clinical Endocrinology & Metabolism, 2006. PMID: 17018654. https://pubmed.ncbi.nlm.nih.gov/17018654/
- The 2026 Prohibited List: International Standard, section S2.2.4 growth hormone releasing factors World Anti-Doping Agency, 2026. WADA 2026 Prohibited List. https://www.wada-ama.org/en/resources/2026-prohibited-list
