Compound comparison
MK-677 (ibutamoren) and ipamorelin are both growth hormone secretagogues that stimulate GH and IGF-1 release via ghrelin receptor agonism, but they differ fundamentally in chemical class, route of administration, and evidence level. MK-677 is a non-peptide, orally active GHSR agonist developed by Merck that completed multiple Phase 2 clinical trials with published peer-reviewed data; it was never submitted for FDA approval and Merck discontinued development. Ipamorelin is a synthetic pentapeptide GHRP (growth hormone releasing peptide) requiring injection, with limited published human clinical data — primarily an original pharmacology study (Raun et al., 1998). Neither compound is FDA-approved for any indication. Both are sold as research-use-only products and are subject to FDA enforcement.
| Attribute | MK-677 (Ibutamoren) | Ipamorelin |
|---|---|---|
| Chemical class | Non-peptide, orally active growth hormone secretagogue (GHS) — ghrelin mimetic | Synthetic pentapeptide growth hormone releasing peptide (GHRP) — ghrelin mimetic |
| Route of administration | Oral (bioavailable as a non-peptide small molecule) | Injectable (subcutaneous); peptide structure is not orally bioavailable |
| Mechanism | Agonist of the growth hormone secretagogue receptor (GHSR); mimics ghrelin to stimulate pulsatile GH release and sustained IGF-1 elevation | Agonist of the growth hormone secretagogue receptor (GHSR); stimulates GH release via ghrelin receptor agonism with preclinical selectivity for GH over cortisol and prolactin |
| Evidence level | Multiple published Phase 2 clinical trials in peer-reviewed journals (Svensson et al., 2000; Bach et al., 2002); sustained IGF-1 elevation and functional outcomes demonstrated; no Phase 3 or FDA approval | One original pharmacology publication (Raun et al., 1998) primarily in animal models; extremely limited published human clinical trial data; no Phase 2/3 trial program comparable to MK-677 |
| Regulatory status | Not FDA-approved for any indication; Merck discontinued clinical development after Phase 2; never submitted for approval; subject to FDA enforcement when marketed outside research-use-only channels | Not FDA-approved for any indication; no clinical development program advanced to regulatory submission; listed on FDA bulk drug substances risk list; subject to FDA enforcement when marketed outside research-use-only channels |
| Supplier availability | Sold by research-use-only vendors; widely marketed online sometimes mislabeled as a SARM; FDA warning letters have addressed such marketing | Sold by research-use-only vendors; commonly marketed alongside CJC-1295 in peptide stacks; subject to FDA warning letters and enforcement actions |
| Community positioning | Widely discussed in fitness and anti-aging communities; presence of Phase 2 data creates a perceived legitimacy gap relative to its unapproved status | Frequently described as the 'safest GHS' in online communities based on preclinical selectivity data; community interpretation, not regulatory or clinical consensus |
MK-677 (ibutamoren) is a non-peptide, orally active growth hormone secretagogue developed by Merck. It acts as an agonist of the growth hormone secretagogue receptor (GHSR), mimicking ghrelin to stimulate GH and IGF-1 release. Unlike peptide-based secretagogues, MK-677 is bioavailable as an oral formulation — a defining characteristic that distinguishes it from injectable GHRPs like ipamorelin.
MK-677 has the strongest published clinical evidence base among non-approved growth hormone secretagogues. Multiple Phase 2 trials demonstrated sustained IGF-1 elevation in humans, including a 12-month study in hip fracture recovery (Bach et al., 2002; PMID 12004295) and a study showing oral MK-677 replicated pulsatile GH profiles seen with IV secretagogues in healthy older adults (Svensson et al., 2000; PMID 10674575). Despite this, Merck discontinued clinical development and never submitted MK-677 for FDA approval for any indication.
MK-677 is widely sold online as a 'research chemical' and is sometimes mislabeled as a SARM despite not being a selective androgen receptor modulator. FDA warning letters have addressed such marketing. The presence of genuine Phase 2 data alongside unapproved research-chemical marketing creates a misleading impression of legitimacy that should be explicitly flagged.
Ipamorelin is a synthetic pentapeptide growth hormone releasing peptide (GHRP) identified in the late 1990s. Like MK-677, it acts as a ghrelin receptor agonist to stimulate GH release, but ipamorelin is a peptide compound administered via injection rather than an orally bioavailable non-peptide. Its original pharmacology was published in the European Journal of Endocrinology (Raun et al., 1998; PMID 9860070), which described selectivity for GH release over cortisol and prolactin in animal models.
Published human clinical trial data for ipamorelin is extremely limited compared to MK-677. The 1998 Raun et al. study is primarily a pharmacology characterization, not a clinical outcomes trial program. No Phase 2 or Phase 3 trials comparable to MK-677's published body of work exist for ipamorelin in the peer-reviewed literature. This creates a significant evidence gap relative to MK-677.
Ipamorelin is widely discussed in online fitness and anti-aging communities, frequently marketed as the 'safest' growth hormone secretagogue based on preclinical selectivity data showing minimal cortisol and prolactin release. This 'safest GHS' framing reflects community interpretation of animal pharmacology data, not a regulatory or clinical consensus. It is commonly stacked with CJC-1295 in telehealth and research-chemical protocols; neither compound is FDA-approved individually or in combination.
MK-677 and ipamorelin are both unapproved growth hormone secretagogues that stimulate GH release via ghrelin receptor agonism, but they differ in three key dimensions. First, route: MK-677 is an orally bioavailable non-peptide, while ipamorelin is an injectable pentapeptide. Second, evidence: MK-677 has multiple published Phase 2 clinical trials with peer-reviewed human data, while ipamorelin's published evidence is primarily a 1998 pharmacology study with limited human clinical data. Third, regulatory history: MK-677 was actively developed by Merck through Phase 2 before discontinuation, while ipamorelin never entered a comparable clinical development program. Neither compound is FDA-approved for any indication. Both are sold as research-use-only products and are subject to FDA enforcement. This comparison documents mechanistic, evidence-level, and regulatory differences; it does not recommend either compound or provide treatment guidance.
Related compounds: MK-677 (Ibutamoren) · Ipamorelin
Source records are stored in the repo and linked from this comparison.
Svensson et al. (2000) study (PMID 10674575) demonstrating that oral MK-677 replicated the pulsatile GH profile seen with IV secretagogues in healthy older adults, with sustained IGF-1 increases over 4 weeks.
Bach et al. (2002) 12-month Phase 2 trial (PMID 12004295) showing MK-677 improved functional status in elderly patients with hip fracture. Despite positive pharmacodynamic data, Merck did not advance MK-677 to FDA approval.
ClinicalTrials.gov registry entry (NCT01016781) for the MK-677 hip fracture recovery trial sponsored by Merck. MK-677 is not FDA-approved for any indication.
Raun et al. (1998) original pharmacology publication (PMID 9860070) describing ipamorelin as a pentapeptide growth hormone secretagogue with selectivity for GH release over cortisol and prolactin in animal models.
FDA page summarizing bulk drug substances that may present significant safety risks in compounding contexts.
FDA warning letter discussing peptide products marketed online and the limits of research-use-only positioning.