Ipamorelin vs MK-677 (Ibutamoren)
Injectable selective secretagogue versus the oral one with a heart failure signal.
The distinction that mattersSame receptor, but MK-677 is an oral non-peptide with sustained rather than pulsatile action — and the only one of the two with a long-term human trial, which found a heart failure signal.
These are not equivalent in evidence MK-677 (Ibutamoren) is rated 3/5 and Ipamorelin is rated 2/5 — a gap of 1 level on our scale. Similar marketing does not mean similar proof.
| Ipamorelin Research Use Only | MK-677 (Ibutamoren) Not a Peptide | |
|---|---|---|
| Evidence rating |
2/5 Limited
Evidence rating 2 out of 5: Limited
|
3/5 Moderate
Evidence rating 3 out of 5: Moderate
|
| Regulatory status | Investigational; phase 2 trials in postoperative ileus were discontinued. Not approved. Common in compounded wellness protocols. | Not a peptide. Investigational drug; development discontinued. Not approved. Prohibited in sport. |
| Category | Growth Hormone Axis | Growth Hormone Axis |
| Drug class | Selective ghrelin receptor (GHS-R1a) agonist — pentapeptide | Non-peptide, orally active ghrelin receptor agonist — listed here because it is universally marketed alongside peptides |
| Route | Subcutaneous (research) | Oral, once daily |
| Half-life | ~2 hours | ~4–6 hours (effects persist ~24h) |
| Studied in | Phase 2 trials for postoperative ileus (development stopped); animal studies on bone and GH secretion. | Multiple phase 2 trials including elderly hip-fracture recovery, sarcopenia, GH deficiency, and a 2-year trial in healthy older adults. |
| Who should avoid it |
|
|
| Legal status | Not FDA-approved. FDA placed several GH-secretagogue peptides under increased compounding scrutiny. | Unapproved investigational drug. Not lawful as a dietary supplement in the US. WADA-prohibited. |
Benefits — Ipamorelin
- Selective GH release
Clean pharmacology: GH rises without the cortisol and prolactin spikes seen with hexarelin or GHRP-6.
- Minimal appetite stimulation
Unlike GHRP-6, it does not produce the intense hunger that makes those peptides impractical.
- Good short-term tolerability
Trial safety data in the ileus program were reassuring over short exposures.
- Synergy with GHRH analogs
The two mechanisms combine to produce a larger pulse than either alone.
Benefits — MK-677 (Ibutamoren)
- Reliable IGF-1 elevation, orally
Trials consistently show IGF-1 increases into the young-adult range in older subjects — no injection required.
- Increases fat-free mass
A 2-year randomized trial in healthy older adults showed a roughly 1.6 kg increase in fat-free mass versus placebo.
- Improved sleep architecture
Studies show increased slow-wave and REM sleep duration.
- Appetite stimulation
Substantial, and potentially useful in cachexia or during recovery from illness.
- Increased bone turnover markers
Suggests bone remodelling activity, though fracture-reduction benefit was not demonstrated.
Risks & cons — Ipamorelin
- No proven clinical benefit
The trials that were run targeted gut motility and were discontinued. Body-composition and recovery claims are untested.
- Unapproved and unregulated
Available only through compounding or grey-market suppliers, with corresponding quality uncertainty.
- Glucose and insulin effects
Raising the GH axis can worsen insulin sensitivity over time.
- Receptor desensitisation
Continuous ghrelin-receptor stimulation blunts the response; effects diminish with sustained use.
- Head/injection-site reactions
Headache, flushing and local reactions are reported.
Risks & cons — MK-677 (Ibutamoren)
- Failed its key clinical trial
The hip-fracture recovery program did not meet endpoints, and development was stopped. Fat-free mass gains did not translate into functional benefit.
- Congestive heart failure signal
A trial in frail elderly patients was halted after an increase in congestive heart failure cases in the treatment arm. This is the most serious concern with the compound.
- Insulin resistance and hyperglycemia
Consistent and dose-dependent; fasting glucose rises and insulin sensitivity falls.
- Fluid retention and oedema
Common, sometimes marked, especially early in use.
- Increased appetite and weight gain
Often unwanted; a substantial fraction of gained weight is not lean tissue.
A comparison is not a recommendation. Neither column is being suggested for you. Which — if either — is appropriate depends on your diagnosis, history and medications, and that is a conversation for a qualified clinician.