GHRP-6 activates the same receptor as ghrelin, the hunger hormone, which is why it drives strong appetite. That off-target effect is one reason it was replaced by the selective GHRP, ipamorelin.
Growth hormone releasing peptides (GHRPs) are synthetic secretagogues that trigger a GH pulse by acting on the ghrelin receptor, not the GHRH receptor. The family includes GHRP-6, GHRP-2, hexarelin, and ipamorelin. The first three are first- and second-generation compounds. Legitimate telehealth prescribes ipamorelin because it produces the GH release without the off-target hormone effects that limited its predecessors [1].
- GHRPs release GH through the ghrelin receptor, a separate pathway from GHRH analogs
- GHRP-6 drives hunger; GHRP-2 and hexarelin raise cortisol and prolactin
- Ipamorelin is the selective GHRP that superseded all three [1]
- A GHRP is usually paired with a GHRH analog for a larger GH response [2]
- No GHRP is FDA-approved; ipamorelin is the only one prescribed through legitimate telehealth [5]
What a GHRP Actually Does
A GHRP binds the growth hormone secretagogue receptor (GHSR), the same receptor the hunger hormone ghrelin uses. Activation triggers a pulse of GH from the pituitary and also blunts somatostatin, the brake on GH release. This is a different mechanism from GHRH analogs such as sermorelin, which is why combining a GHRP with a GHRH analog produces a larger GH response than either alone [2].
One letter apart, two different receptors. GHRPs act on the ghrelin receptor (GHSR). GHRH analogs like sermorelin act on the GHRH receptor. The distinction is why the two classes stack instead of overlapping.
Because the GHSR is the ghrelin receptor, the earliest GHRPs carried ghrelin-like side effects: hunger, and in some cases a rise in cortisol and prolactin. The history of the class is essentially a search for a compound that keeps the GH release while shedding those off-target effects. Ipamorelin is where that search landed [1].
GHRP-6: The First Generation
GHRP-6 was among the first peptides shown to release GH through the ghrelin pathway. It works, but it drives strong hunger because it activates the ghrelin receptor that governs appetite. In humans, GHRP-6 combined with GHRH produces a much larger GH response than either agent alone, which established the two-pathway principle [2]. The appetite stimulation and dated profile are why it is not a current telehealth product.
GHRP-2: More Potent, Still Off-Target
GHRP-2 is more potent than GHRP-6 at releasing GH and provokes less hunger, but it raises cortisol and prolactin more than the selective options. Those off-target hormone rises are the trade-off that kept it from becoming a mainstream prescribed peptide. It remains a research and grey-market compound rather than a standard telehealth prescription.
Hexarelin: Potent but Self-Limiting
Hexarelin is the most potent of the early GHRPs but causes the fastest receptor desensitization, so its GH effect fades with continued use. It also raises cortisol and prolactin. It is not used in standard telehealth protocols.
Ipamorelin: The Selective GHRP
Ipamorelin is the fourth-generation GHRP and the one used in current practice. In the study that introduced it, it released GH with a potency similar to GHRP-6 but without the rise in ACTH, cortisol, or prolactin [1]. That selectivity is the entire reason it replaced the earlier compounds. Its human efficacy data is thin: the one published controlled trial, in postoperative ileus, missed its primary endpoint [3]. See the full ipamorelin guide for detail.
The GHRPs Compared
| GHRP | Generation | Main drawback | Prescribed today |
|---|---|---|---|
| GHRP-6 | First | Strong hunger (ghrelin effect) | No |
| GHRP-2 | Second | Raises cortisol and prolactin | No |
| Hexarelin | Third | Desensitizes quickly; raises cortisol | No |
| Ipamorelin | Fourth | Thin human efficacy data | Yes |
Why a GHRP Is Paired With a GHRH Analog
A GHRP alone is rarely the whole protocol. The larger, more reproducible GH response comes from combining a GHRP with a GHRH analog, since the two hit separate receptors and the somatostatin brake is lifted at the same time [2]. In current practice that means ipamorelin paired with sermorelin [4] or CJC-1295.
- Ipamorelin supplies the ghrelin-receptor pulse
- The GHRH analog supplies the GHRH-receptor signal
- Together they lift somatostatin and raise pulse amplitude
- Ipamorelin's selectivity avoids the cortisol and prolactin rise of older GHRPs [1]
GHRP-6 and GHRP-2 have no legitimate prescription pathway. SystemLabs prescribes ipamorelin, the selective modern GHRP, alongside a baseline IGF-1 so the protocol is measured from the start.
Why the Off-Target Effects Matter
The reason first-generation GHRPs fell out of clinical use is not that they failed to release GH. It is what else they released. Activating the ghrelin receptor broadly, as GHRP-6 does, drives hunger through the same pathway that governs appetite. Raising cortisol and prolactin, as GHRP-2 and hexarelin do, is the more clinically relevant problem.
- Cortisol elevation works against the body composition and recovery goals people take a GHRP for
- Prolactin elevation can blunt libido and, over time, affect the reproductive axis
- GHRP-6 appetite stimulation is counterproductive for anyone targeting fat loss
- Ipamorelin avoids all three by acting selectively at the secretagogue receptor [1]
This is the practical case for selectivity. A peptide that raises GH cleanly, without pulling cortisol and prolactin up with it, is a better tool for the outcomes patients actually want. It is also why the safety argument for ipamorelin rests on receptor selectivity rather than on long-term human trials, which do not exist for any GHRP.
Regulatory Status
No GHRP is FDA-approved. Ipamorelin is compounded and appears on FDA's list of bulk substances that may present significant safety risks [5]. GHRP-6, GHRP-2, and hexarelin have no legitimate prescription pathway in the US. All GHRPs are banned in competition by the World Anti-Doping Agency as growth hormone secretagogues [6].
Bottom Line
Frequently Asked Questions
What is the difference between GHRP-6 and GHRP-2?
Both release GH through the ghrelin receptor. GHRP-6 drives strong hunger and is less potent. GHRP-2 is more potent and stimulates less appetite, but raises cortisol and prolactin more than the selective options. Neither is prescribed through legitimate telehealth today; ipamorelin replaced both.
Is ipamorelin a GHRP?
Yes. Ipamorelin is a growth hormone releasing peptide, the fourth-generation and most selective member of the class. In the study that introduced it, it released GH without the rise in ACTH, cortisol, or prolactin seen with GHRP-6 and GHRP-2 [1]. That selectivity is why it is the GHRP used in current practice.
Are GHRP-6 and GHRP-2 still used?
Not in legitimate telehealth. GHRP-6 and GHRP-2 are older compounds with off-target effects: GHRP-6 causes strong hunger, and GHRP-2 raises cortisol and prolactin. Neither has an FDA-approved or standard prescription pathway. They persist mainly as research chemicals and grey-market products, which carry no quality assurance.
Do GHRPs build muscle?
GHRPs raise GH and downstream IGF-1, which support lean mass, but no GHRP has controlled human trial data showing muscle growth on its own. Ipamorelin's only published efficacy trial, in postoperative ileus, missed its endpoint [3]. Any lean mass benefit depends on resistance training and is not established from GHRP monotherapy.
Which GHRP is best?
Ipamorelin, by the standard of selectivity and safety. It produces a comparable GH pulse to GHRP-6 without the cortisol and prolactin rise of GHRP-2 or the appetite spike of GHRP-6 [1]. It is also the only GHRP with a legitimate prescription pathway. It is typically paired with a GHRH analog rather than run alone [2].
References
- 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/
- Prospective, randomized, controlled, proof-of-concept study of the ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patients International Journal of Colorectal Disease, 2014. PMID: 25331030. https://pubmed.ncbi.nlm.nih.gov/25331030/
- 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/
- Certain bulk drug substances for use in compounding that may present significant safety risks FDA.gov, Human Drug Compounding, 2026. FDA Category 2 bulk substances list. https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
- 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
