MK-677 (Ibutamoren)
An orally active, non-peptide ghrelin-receptor agonist that raises GH and IGF-1 levels. Human trials were conducted, but development was discontinued and it was never approved.
HGH 191AA (Somatropin)
Recombinant human growth hormone identical to the 191-amino-acid endogenous protein, approved by prescription for GH deficiency, pediatric growth disorders, and several other indications.
What each one is
Somatropin is recombinant 191-amino-acid human growth hormone — an approved biologic medicine with decades of clinical use in growth disorders, wasting conditions, and replacement therapy. MK-677 (ibutamoren) is a small non-peptide molecule that mimics ghrelin, stimulating the pituitary to release more of the body’s own GH.
Evidence
Somatropin’s evidence base includes thousands of patients across approved indications with defined benefit-risk profiles. MK-677 has real human trials — including long-term studies in elderly and sarcopenic populations — but no approved indication: its development program never demonstrated a benefit that outweighed its side-effect profile.
The oral advantage is real but insufficient
MK-677’s main appeal is that it is oral. That is a genuine formulation advantage over injectable peptides. It does not rescue the compound from its tolerability issues — appetite stimulation, water retention, fasting glucose deterioration — or from the absence of any approved use.
Safety
Somatropin’s risks are well characterized and clinically managed. MK-677’s human data show consistent metabolic downsides, and its long-term safety in unsupervised use is unknown. Gray-market versions of both add identity and sterility risk.
Regulatory status
Somatropin is a prescription biologic with approved products worldwide. MK-677 is unapproved everywhere, prohibited in sport, and has been the subject of regulatory warnings — including for its appearance in supplements.
Frequently Asked Questions
Is MK-677 "just oral HGH"?
No. It is an indirect stimulant of endogenous GH with a different pharmacodynamic fingerprint, different side effects, and no approved indication.
Did MK-677 fail its trials?
It completed multiple trials but never won approval — efficacy signals did not outweigh side effects for any studied population. That history is the product’s actual record.
Why do people compare them at all?
Because both end in "more GH signaling," and because the oral-versus-injected framing sells. The pharmacological realities are far apart.
Evidence tier: Clinical-stage · Last reviewed: 2026-09-05 · Sources cited below.