Short answer: they hit the same receptor, but MK-677 has much more evidence, good and bad. MK-677 (ibutamoren) and ipamorelin both activate the ghrelin receptor and raise growth hormone. MK-677 is a pill that keeps GH and IGF-1 raised all day and has 17 human trials, some lasting a year; it raised fat-free mass but also appetite, water retention and blood sugar. Ipamorelin is an injected peptide that triggers a short GH pulse and has only two published human studies, neither on muscle or fat. Neither is approved, and both are banned in sport.
MK-677 vs ipamorelin at a glance
| MK-677 | Ipamorelin | |
|---|---|---|
| What it is | GH secretagogue (ghrelin receptor agonist) | GH secretagogue (ghrelin receptor agonist pentapeptide) |
| Approval | Not approved; furthest stage: Phase 3 | Not approved; furthest stage: Phase 2 |
| Human studies (counted in our records) | 17 | 2 |
| Half-life | Not established in humans | ~2 h |
| Testosterone suppression score | 1/3 | Not established |
| Liver risk score | 1/3 | Not established |
| Evidence score | 3/3 | 1/3 |
| WADA | Prohibited at all times (S2.2.4 Growth hormone releasing factors) | Prohibited at all times (S2.2.4 Growth hormone releasing factors) |
| How it is taken | By mouth, once a day in trials | Injection (IV in the human studies) |
| GH pattern | Sustained rise; IGF-1 up 1.5-fold over 12 months | Single short pulse, peak about 40 min |
| SwissChems product | MK-677 (Ibutamoren), (10mg/capsule) 60 Capsules | Ipamorelin 2mg |
Scores run from 0 (none) to 3 (high); see our methodology. Data from the SARMs database.
Source: Sarmguide compound database; MK-677: ClinicalTrials.gov NCT06948214: Phase 3 Study of LUM-201 in Children With Growth Hormone Deficiency (2026).
How they work
Both copy ghrelin, the hunger hormone, at its receptor in the pituitary and hypothalamus. MK-677 is a non-peptide small molecule that works by mouth and keeps the signal on: in older adults, 25 mg/day for 12 months raised 24-hour GH 1.8-fold and IGF-1 1.5-fold. Ipamorelin is a peptide that must be injected; in healthy men a single IV dose produced one GH pulse that peaked at about 40 minutes and faded. Ghrelin also drives appetite, which is why hunger is MK-677’s most common side effect.
What the trials show
| Outcome | MK-677 | Ipamorelin |
|---|---|---|
| Fat-free mass | +1.1 kg vs −0.5 kg on placebo over 12 months (older adults); strength unchanged | Not studied in humans |
| Sleep | About 50% more deep sleep in a small 14-person study | Not studied |
| Bone | With alendronate, femoral-neck density rose more (4.2% vs 2.5%) | Animal data only |
| Clinical outcomes | No effect on Alzheimer’s progression; hip-fracture trial stopped over heart failure | No benefit for gut recovery after surgery |
| Children with GH deficiency | Growth rate rose (less than injected GH); Phase 3 as LUM-201 | Not studied |
Side effects
MK-677’s side effects are well documented: more appetite (67% vs 36% on placebo in a 12-month trial), leg swelling, muscle and joint pain, higher fasting glucose and lower insulin sensitivity, a small rise in prolactin and cortisol, and in frail older adults after hip fracture, more heart failure (4 of 62 vs 1 of 61) with higher blood pressure. Ipamorelin has much less data: in the surgery trial adverse events were as common as with placebo, but the FDA cites serious adverse events, including death, with IV use, lists it as a significant safety risk for outsourcing facilities, and warns about immune reactions from impurities. See MK-677 side effects.
Half-life
No human plasma half-life has been published for MK-677; its GH effect is described as long-acting (about 24 hours). Ipamorelin’s half-life is about 2 hours after IV infusion.
Legal status and sport
Neither is approved. In the US, MK-677 (ibutamoren mesylate) is in FDA Category 2 for compounding because of the heart-failure signal, and FDA warning letters in December 2025 named products sold as MK-677. Ipamorelin is in Category 2 for outsourcing facilities. Both are named under WADA S2.2.4 (growth hormone secretagogues), prohibited at all times.
Verdict
MK-677 is the better-studied of the two by a wide margin: it raises GH and IGF-1 for a full day, added about 1 kg of fat-free mass in older adults, and comes with documented costs in appetite, fluid, blood sugar and, in frail patients, heart failure. Ipamorelin gives a short GH pulse with little human data on either benefit or harm. Related: MK-677 vs HGH · tesamorelin vs ipamorelin · best growth hormone peptides
Frequently asked questions
Is MK-677 better than ipamorelin?
MK-677 has far more evidenceEvidence: Trial
MK-677 has far more human data, including 12-month trials in which fat-free mass rose 1.1 kg, but also documented hunger, water retention and higher blood sugar. Ipamorelin has little human data either way.
What is the difference between MK-677 and ipamorelin?
Same receptor, different drugsEvidence: Human data
Both act on the ghrelin receptor. MK-677 is an oral small molecule with a sustained effect; ipamorelin is an injected peptide that produces a short GH pulse.
Does ipamorelin increase appetite like MK-677?
Unknown for ipamorelinEvidence: Trial
MK-677 clearly does (67% vs 36% on placebo). Ipamorelin's effect on appetite has not been measured in a published human study.
Can you take MK-677 and ipamorelin together?
Never studiedEvidence: Limited
No study has tested the combination. They act on the same receptor, so combining them adds risk without a clear rationale.
Which raises IGF-1 more, MK-677 or ipamorelin?
MK-677, as far as knownEvidence: Trial
MK-677 raised IGF-1 about 1.5-fold over 12 months in older adults. Ipamorelin's effect on IGF-1 with repeated use has not been reported in a published human study.
Are MK-677 and ipamorelin legal?
Not approved; banned in sportEvidence: Law
Neither is approved; both are on FDA Category 2 safety lists for compounding. Both are banned in sport under WADA S2.2.4.
Sources
- Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial
- Prolonged oral treatment with MK-677, a novel growth hormone secretagogue, improves sleep quality in man
- Effect of alendronate and MK-677 (a growth hormone secretagogue), individually and in combination, on markers of bone turnover and bone mineral density in postmenopausal osteoporotic women
- Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial
- MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study
- Pharmacokinetic-pharmacodynamic modeling of ipamorelin, a growth hormone releasing peptide, in human volunteers
- Prospective, randomized, controlled, proof-of-concept study of the Ghrelin mimetic ipamorelin for the management of postoperative ileus in bowel resection patients
- Ipamorelin, the first selective growth hormone secretagogue
- FDA Briefing Document, Pharmacy Compounding Advisory Committee, 29 October 2024: Ibutamoren Mesylate
- FDA: Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (Category 2 list; content current as of 22 Apr 2026)
- FDA Warning Letter to an online seller of products marketed as SARMs (MARCS-CMS 719257), 12 December 2025
- World Anti-Doping Code International Standard: Prohibited List 2026
