MK-677 has the largest human safety dataset of any growth hormone secretagogue on this page, a 2-year randomized trial in 65 older adults. Ipamorelin has one published human efficacy trial, and it missed its primary endpoint.
Ipamorelin and MK-677 both work through the same target, the ghrelin receptor, but almost nothing else about them matches. Ipamorelin is an injectable peptide, usually formulated through a compounding pharmacy alongside a GHRH analog. MK-677 is an oral, non-peptide small molecule most often sourced outside any licensed pharmacy. This guide compares the mechanism, the human evidence each one actually has, and where each stands with FDA and anti-doping authorities.
- Both bind the ghrelin receptor, but ipamorelin was designed for selectivity while MK-677 is the original, non-selective ghrelin mimetic tested in a real long-term human trial [1][2]
- MK-677's 2-year RCT in 65 older adults found increased fat-free mass but also raised fasting glucose, lowered insulin sensitivity, and raised cortisol by 47 nmol/L [2]
- Ipamorelin's cortisol-sparing claim comes from swine and rat data; MK-677 is the one of the two actually shown, in people, to raise cortisol [1][2]
- Neither is FDA-approved. Both sit in FDA's Category 2 for compounding safety risk, and both were voted against by the same October 29, 2024 advisory committee meeting [4]
- MK-677 is typically sold outside any prescription or compounding-pharmacy channel; ipamorelin, while also flagged, is at least dispensed through licensed 503A pharmacies inside legitimate telehealth programs
- Both are prohibited in sport at all times under the 2026 WADA Prohibited List [6]
| Term | What It Means |
|---|---|
| Ghrelin receptor (GHS-R1a) | The receptor both compounds bind. Its natural activator is ghrelin, the hormone that signals hunger and also triggers a GH pulse. |
| Peptide vs non-peptide secretagogue | Ipamorelin is a short amino-acid chain that must be injected. MK-677 is a small organic molecule stable enough to survive digestion, which is why it is taken orally. |
| 503A Category 2 | The FDA designation for a bulk substance flagged as presenting a safety risk in compounding. It does not mean banned outright, but it means a 503A pharmacy is not supposed to compound it. |
Same Receptor, Different Selectivity Claims
Ipamorelin was introduced as the first selective growth hormone secretagogue, triggering a GH pulse without raising ACTH or cortisol even at more than 200 times its GH dose in the foundational study [1]. That selectivity was measured in swine and rats. MK-677 makes no selectivity claim. It is the compound the field has actually tested in people for years, and its own 2-year randomized trial in older adults found cortisol rose 47 nmol/L in the treatment group [2], the opposite of the cortisol-sparing profile ipamorelin is marketed on. Judged purely on what has been measured in humans, MK-677 is the one shown to raise cortisol. The same selective-vs-nonselective question comes up against GHRP-6, the older peptide ipamorelin was designed to replace.
The "Same Receptor, Different Selectivity Claims" section above is background. A prescriber is what turns it into a protocol. SystemLabs is the provider we found doing that, at $179 a month, checking baseline IGF-1 levels before it prescribes, then formulates dose on clinical indication.
The Human Evidence, Read Honestly
Ipamorelin's only published human efficacy trial tested it for postoperative ileus and missed its primary endpoint, with adverse events close to placebo [3]. That is a short surgical-population trial, not months of data on body composition. MK-677's record is longer and more detailed: a 2-year, double-blind, randomized trial in 65 healthy adults aged 60 to 81 found fat-free mass rose 1.1 kg versus a 0.5 kg loss on placebo, with no significant change in abdominal visceral fat or total fat mass [2].
- Fasting glucose rose 0.3 mmol/L and insulin sensitivity decreased in the MK-677 group [2]
- The most frequent side effects were increased appetite that subsided within a few months, mild lower-extremity edema, and muscle pain [2]
- Increased fat-free mass did not translate into measured strength or function gains [2]
- LDL cholesterol improved modestly, one of the few clearly favorable findings [2]
MK-677 has more real human outcome data than ipamorelin, and that data is itself the reason for caution: a real glucose and cortisol signal over 2 years, with no matching strength benefit despite the fat-free mass gain.
Route and Regulatory Status
Neither compound is FDA-approved, and both sit in FDA's Category 2 for bulk substances presenting a compounding safety risk [4]. The same October 29, 2024 Pharmacy Compounding Advisory Committee meeting that voted 0 to 12 against adding ipamorelin to the 503A list also considered and voted against ibutamoren mesylate, the chemical name for MK-677, with committee members citing insufficient efficacy and safety data and raising concerns about fluid retention, cardiac effects, and hyperglycemia [4][5]. The practical difference is where each one actually gets sold. Ipamorelin is dispensed through licensed 503A or 503B pharmacies inside prescription-based telehealth programs. MK-677 is overwhelmingly sold as a raw research chemical with no prescriber, no compounding pharmacy, and no Certificate of Analysis requirement behind it.
| Factor | Ipamorelin | MK-677 (ibutamoren) |
|---|---|---|
| Route | Subcutaneous injection | Oral capsule or powder |
| Dosing frequency | Nightly, typically stacked with a GHRH analog | Once daily |
| Human trial evidence | One trial, missed its endpoint [3] | 2-year RCT, real outcome data [2] |
| Cortisol effect measured in people | Not measured in humans | Raised 47 nmol/L [2] |
| Typical source | Licensed compounding pharmacy, by prescription | Unregulated research-chemical sellers |
| Sport status | Prohibited at all times [6] | Prohibited at all times [6] |
What the Trial Population Does and Does Not Tell You
The MK-677 evidence base has a boundary worth naming directly. The 2-year trial enrolled adults aged 60 to 81 [2], a population already losing fat-free mass to age-related decline. Its fat-free mass and glucose findings describe that group, not a younger adult using the compound for recomposition or performance, where no comparable controlled data exists for either compound. Dosing frequency is a separate practical difference: MK-677's oral, once-daily dose does not require reconstitution or a needle, while ipamorelin is a nightly injection almost always paired with a GHRH analog on its own separate schedule.
The Bottom Line
MK-677 gives up the injection but brings the only real long-term human data on this receptor pathway, and that data shows a glucose and cortisol cost alongside the fat-free mass gain, with no measured strength benefit. Ipamorelin brings the cleaner selectivity story, but it is animal data, and its thin human trial record does not settle the question either way. The variable that matters most in practice is not the peptide, it is the channel: ipamorelin reaches most patients through a prescriber and a licensed pharmacy with lab monitoring available, while MK-677 usually does not. Neither belongs in a self-sourced routine without a baseline IGF-1 and glucose panel.
The MK-677 trial data makes the case for monitoring, not against secretagogues generally. SystemLabs tests IGF-1 before prescribing and stacks ipamorelin with a GHRH analog on clinical indication, so the dose is set against your labs and checked at 90 days.
Frequently Asked Questions
Is MK-677 the same as ipamorelin?
No. Both bind the ghrelin receptor, but ipamorelin is an injectable peptide with an animal-data selectivity claim, while MK-677 (ibutamoren) is an oral, non-peptide compound with a real 2-year human trial showing it raises cortisol and fasting glucose [1][2]. They are different molecules with different evidence bases.
Which is safer, ipamorelin or MK-677?
Neither has an established safety record, but the risks differ. MK-677's own trial documented a fasting glucose increase, reduced insulin sensitivity, and a 47 nmol/L cortisol rise over 2 years [2]. Ipamorelin's selectivity claim would predict a milder metabolic profile, but that claim has not been tested in a comparable human trial [1][3].
Does MK-677 raise cortisol?
Yes, in its 2-year randomized trial in older adults, cortisol rose by an average of 47 nmol/L in the MK-677 group [2]. That is the opposite of the cortisol-sparing profile claimed for ipamorelin, and it is measured in people rather than inferred from animal data.
Can you take ipamorelin and MK-677 together?
This has not been studied, and combining two ghrelin-receptor agonists has no established rationale over using either one on a monitored dose. A prescriber working from a baseline IGF-1 is the person to make that call, not a self-directed stack.
References
- Ipamorelin, the first selective growth hormone secretagogue European Journal of Endocrinology, 1998. PMID: 9849822. https://pubmed.ncbi.nlm.nih.gov/9849822/
- Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial Annals of Internal Medicine, 2008. PMID: 18981485. https://pubmed.ncbi.nlm.nih.gov/18981485/
- 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/
- Summary minutes of the Pharmacy Compounding Advisory Committee meeting, October 29, 2024 FDA Advisory Committee, 2024. PCAC summary minutes, ibutamoren mesylate and ipamorelin both considered. https://www.fda.gov/media/185412/download
- FDA Briefing Document, Pharmacy Compounding Advisory Committee meeting FDA Advisory Committee, 2024. PCAC briefing document. https://www.fda.gov/media/182085/download
- 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
