Which is better, ipamorelin or MK-677 (ibutamoren)?
On evidence, MK-677 is far better characterized (human_rct, including a 2 year trial in 65 older adults) than ipamorelin (animal_only for marketed uses). But that evidence shows modest lean mass gain with no functional benefit and real harms, and FDA keeps MK-677 in both 503A and 503B Category 2 over the heart failure signal, while ipamorelin's nomination was withdrawn after its own Category 2 listing. Neither has a lawful US access path, so there is no scenario where one is a recommended choice over the other. [1] [2] [4] [8] [9] [10] [12]
How do ipamorelin and MK-677 (ibutamoren) compare?
| Dimension | Ipamorelin | MK-677 (ibutamoren) |
|---|---|---|
| Molecule and route [1] [6] | Synthetic pentapeptide, given by injection (subcutaneous as sold; intravenous in the only human trial). | Non peptide small molecule taken orally once daily; its half life supports daily dosing. |
| Evidence grade [2] [3] [4] [5] [7] | Animal only for GH related uses: selective GH release in rats and pigs, bone growth in rats. | Human RCT: several randomized placebo controlled trials from 4 weeks to 2 years in older adults, obese men, and people with Alzheimer disease. |
| Human body composition data [1] [4] [5] | None published; the only human RCT measured recovery of bowel function after surgery and found no significant benefit. | Two years of 25 mg daily in 65 adults aged 60 to 81: fat free mass up about 1.1 kg versus placebo, no gain in strength or function. Eight weeks in 24 obese men: fat free mass up about 3 kg, no fat loss. |
| Hormonal selectivity [2] [6] | In animals it did not raise ACTH, cortisol, or prolactin even at 200 times the GH ED50. | Transient rises in cortisol and prolactin reported; raises 24 hour GH and IGF-1 into the young adult range in older people. |
| Safety signals [1] [4] [8] [10] | No signal versus placebo over 7 days of intravenous dosing; long term effects untested. FDA cited immunogenicity from aggregation and impurities. | Increased appetite, edema, muscle pain, higher fasting glucose and reduced insulin sensitivity over 2 years; a hip fracture trial was terminated early for a possible congestive heart failure signal. |
| Literature dosing [1] [4] [6] | Not established for GH use; the human trial used 0.03 mg/kg intravenously twice daily for up to 7 days. | Trials used 25 mg orally once daily, with 2 mg and 50 mg arms in early studies. Research doses only. |
| FDA compounding status [9] [10] [11] | 503A Category 2 in September 2023; nominations withdrawn in 2024, now listed as a withdrawn nomination. Ipamorelin acetate remains in 503B Category 2. | 503B Category 2 since December 2022 and 503A Category 2 since September 2023, citing the heart failure risk; still in both as of April 2026. It also may not be sold as a dietary supplement. |
| Note: Both are prohibited at all times under WADA section S2. | ||
Evidence grade and regulatory status
Pulled from each peptide’s own record, so it stays in step with the peptide pages.
| Attribute | Ipamorelin | MK-677 (ibutamoren) |
|---|---|---|
| Class | Synthetic pentapeptide growth hormone secretagogue; selective agonist at the ghrelin receptor (GHS-R1a) | Oral non peptide growth hormone secretagogue (small molecule ghrelin receptor agonist) |
| What it is | Growth hormone releaser acting on the hunger hormone (ghrelin) receptor; raised GH in animals and one small study in men; its only randomized trial failed. | Oral ghrelin mimetic with real RCTs: raises IGF-1 and lean mass modestly, raises glucose and appetite, a heart failure signal stopped development. Not approved. |
| Evidence | Evidence: Animal-only evidence | Evidence: Human RCT evidence |
| FDA status | Regulatory: Removed from Category 2 (Apr 2026) | Regulatory: Not eligible for compounding |
| Compounding | Not FDA approved for any use and never approved anywhere. FDA placed ipamorelin (free base and acetate) on the 503A Category 2 list on September 29, 2023, citing immunogenicity risk, peptide related impurities, and lack of safety data for the compounded routes. The nominators withdrew the 503A nominations in September 2024 and FDA's April 2026 update moved it to the list of nominated but withdrawn substances rather than Category 1 or the bulks list. Ipamorelin acetate also remains in 503B Category 2 (added September 29, 2023) on the FDA page current as of April 22, 2026. It was not among the peptides the Pharmacy Compounding Advisory Committee reviewed in July 2026. Because it has no active nomination, is not on the 503A bulks list, and is not a component of an approved drug, licensed 503A pharmacies and 503B outsourcing facilities have no lawful basis to compound it. | Not FDA approved for any use. FDA placed ibutamoren mesylate in 503B Category 2 on December 29, 2022 and in 503A Category 2 on September 29, 2023, citing the potential for congestive heart failure based on the terminated hip fracture trial. As of the FDA page current to April 22, 2026, it remains in both categories, so no licensed pharmacy or outsourcing facility can lawfully compound it. It was not among the substances withdrawn from Category 2 in April 2026. It is widely sold online as a research chemical or mislabeled supplement. |
| WADA | WADA: WADA prohibited | WADA: WADA prohibited |
| Routes | Subcutaneous injection (as sold, no human pharmacokinetic publication), Intravenous infusion (human ileus trial), Intranasal (anti-doping metabolite study only) | Oral capsule or tablet, once daily (all trials and as sold) |
| Typical cost | Not available through licensed channels. Products sold as research chemicals are not lawful for human use and are not verified for identity or purity. | Not available through licensed US channels. Products sold as research chemicals are not lawful for human use and are not verified for identity or purity. |
| Last verified |
Has ipamorelin been tested directly against MK-677 (ibutamoren)?
No published trial has compared ipamorelin and MK-677 (ibutamoren) directly. The dimensions above come from separate studies and labels, and cross-trial comparisons are less reliable than a direct trial.
What do ipamorelin and MK-677 (ibutamoren) cost?
| Dimension | Ipamorelin | MK-677 (ibutamoren) |
|---|---|---|
| Typical cost | Not available through licensed channels. Products sold as research chemicals are not lawful for human use and are not verified for identity or purity. | Not available through licensed US channels. Products sold as research chemicals are not lawful for human use and are not verified for identity or purity. |
| Price detail | Ipamorelin price by channel | Price index in progress |
Where a price index exists, the range is the cash price per month across branded, compounded, and telehealth channels, without insurance. The cost pages give each channel separately with its sources. Otherwise the typical cost from the peptide record is shown. Legal access depends on your state: see peptide legality by state.
Frequently asked questions
Do ipamorelin and MK-677 work the same way?
Yes, both activate the ghrelin receptor (GHS-R1a) to release growth hormone. The difference is form: ipamorelin is an injected peptide, MK-677 is an oral small molecule taken once daily. [2] [6]
Which has better human evidence?
MK-677, by a wide margin. It has randomized trials up to 2 years long, including one where 25 mg daily raised fat free mass by about 1.1 kg versus placebo in older adults. Ipamorelin has no human trial measuring IGF-1 or body composition; its human growth hormone data are one small IV pharmacology study showing growth hormone release in healthy men. [1] [4] [12]
Does MK-677 build muscle strength?
Not in the best trial. The 2 year study found a lean mass gain without any improvement in strength or physical function, along with higher fasting glucose and reduced insulin sensitivity. [4]
Why does FDA consider MK-677 a safety risk?
A phase 2b trial in hip fracture patients was stopped early because of a possible congestive heart failure signal, and FDA cited that when it placed ibutamoren in both the 503A and 503B Category 2 lists. [8] [9]
Can I get either one legally?
No. Neither is FDA approved, MK-677 is in Category 2 for both pharmacy types, and ipamorelin has no active nomination or bulks list entry, so licensed pharmacies cannot compound either. Products sold as research chemicals or supplements are not lawful for human use. [9] [10]
Conditions studied
From the blog
- Peptide stacks: what each common component has shown alone
No trial has tested a multi-peptide stack for muscle growth or fat loss. Nine common stack components ranked by their own human evidence, legal status, and WADA status. No protocols.
- Peptides for muscle growth, ranked by human evidence
MK-677, sermorelin, tesamorelin, CJC-1295, IGF-1 LR3, and more ranked by human evidence. None is approved for muscle growth, and all ten are banned in tested sport.
Sources
Numbered citations above point to these primary sources. PubMed entries link to the indexed abstract.
- [1]Beck DE, Sweeney WB, McCarter MD; Ipamorelin 201 Study Group. Prospective, randomized, controlled, proof-of-concept study of the ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patients. Int J Colorectal Dis 2014PubMed 25331030, 2014
- [2]Raun K et al. Ipamorelin, the first selective growth hormone secretagogue. Eur J Endocrinol 1998PubMed 9849822, 1998
- [3]Johansen PB et al. Ipamorelin, a new growth-hormone-releasing peptide, induces longitudinal bone growth in rats. Growth Horm IGF Res 1999PubMed 10373343, 1999
- [4]Nass R et al. Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Ann Intern Med 2008PubMed 18981485, 2008
- [5]Svensson J et al. Two-month treatment of obese subjects with the oral GH secretagogue MK-677 increases GH secretion, fat-free mass, and energy expenditure. J Clin Endocrinol Metab 1998PubMed 9467542, 1998
- [6]Chapman IM et al. Stimulation of the GH-IGF-I axis by daily oral administration of a GH secretogogue (MK-677) in healthy elderly subjects. J Clin Endocrinol Metab 1996PubMed 8954023, 1996
- [7]Sevigny JJ et al. Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial. Neurology 2008PubMed 19015485, 2008
- [8]Adunsky A et al. MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study. Arch Gerontol Geriatr 2011PubMed 21067829, 2011
- [9]FDA: Certain bulk drug substances for use in compounding may present significant safety risks (Category 2 list, content current as of April 22, 2026)FDA
- [10]FDA: Bulk drug substances used in compounding under section 503A of the FD&C Act (503A bulks list, Category 1, 2, and 3 lists, and withdrawn nominations)FDA
- [11]WADA Prohibited List, section S2 (growth hormone secretagogues, including ipamorelin and ibutamoren)WADA
- [12]Gobburu JV et al. Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers. Pharm Res 1999PubMed 10496658, 1999
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