Short answer: HGH (somatropin) is growth hormone itself, FDA approved for diagnosed GH deficiency and some childhood growth disorders.1 MK-677 (ibutamoren) is an unapproved pill that makes the pituitary release more of its own GH.2 In older adults it raised GH and IGF-1 into the young-adult range but also raised fasting glucose,3 and one trial stopped early over heart failure.4
| HGH (somatropin, e.g. Genotropin) | MK-677 (ibutamoren) | |
|---|---|---|
| What it is | Recombinant human growth hormone1 | Oral ghrelin mimetic that boosts the body's own GH pulses2 |
| Approval status | FDA approved (Genotropin since 1987)1 | Not approved; FDA compounding Category 25 |
| Approved uses | Adults with GH deficiency; children with GH deficiency, Prader-Willi, Turner syndrome, small for gestational age or idiopathic short stature1 | None |
| Dose | Label, adult GH deficiency: about 0.2 mg/day to start (0.15 to 0.30), adjusted by IGF-1; or up to 0.04 then 0.08 mg/kg/week1 | Studied: 25 mg by mouth once daily3 |
| Route | Injection under the skin1 | By mouth |
| Half-life | 3.0 hours under the skin in adults with GH deficiency1 | Not stated in the trial abstracts cited here |
| Time to peak (Tmax) | About 5.9 hours under the skin (Genotropin study)1 | Not stated in the trial abstracts cited here |
| Glucose | Label warns it may unmask glucose intolerance or diabetes1 | Fasting glucose up in older adults;3 5.4 to 6.8 mmol/L at 4 weeks in a 1996 trial2 |
| Other key warnings | Fluid retention, raised pressure in the skull; do not use with active cancer or acute critical illness1 | Hip fracture trial stopped early for a heart failure signal4 |
| Sport | WADA S2.2.3 (growth hormone)6 | WADA S2.2.4 (named)6 |
Somatropin is the hormone itself, so it works whether or not the pituitary can make GH, which is why it is approved for diagnosed deficiency.1 MK-677 works upstream: in older adults it increased the height of the body's own GH pulses without changing how many there were.2
HGH: in six placebo-controlled Genotropin trials in 172 adults with GH deficiency, body composition improved over 6 months.1 The label ties dosing to IGF-1 and to side effects, and the weekly dose is split into 6 or 7 injections.1
MK-677: in a 2-year trial of 65 healthy adults aged 60 to 81, 25 mg daily raised GH and IGF-1 to young-adult levels and lean mass by 1.1 kg, but strength and function did not change, weight rose 2.7 kg, and insulin sensitivity fell.3 In 123 hip fracture patients the trial stopped early for a heart failure signal,4 and in 563 people with Alzheimer disease it did not slow progression.7
These are different populations and no trial compared the two directly. These are study protocols, not personalized advice; confirm any dosing with your prescriber.