Ibutamoren / Nutrobal, Oral GH Secretagogue
A potent oral ghrelin mimetic that stimulates growth hormone and IGF-1 release from the pituitary. Unique among GH-axis compounds for its oral bioavailability, no injection required. Backed by a 2-year randomised controlled trial showing sustained GH and IGF-1 elevation, improved lean mass, and bone density. Technically a small molecule rather than a peptide, but universally grouped with GH peptides in research and clinical contexts.
01, Research Summary
MK-677 has a more substantial human clinical dataset than most compounds in the GH secretagogue category, anchored by a landmark 2-year randomised controlled trial that provides unusually long-duration safety and efficacy data.
Sustained GH and IGF-1 elevation with improved body composition. The landmark 2-year trial in adults over 60 showed MK-677 maintained elevated GH and IGF-1 throughout the full treatment period, with significant improvements in lean body mass and bone mineral density versus placebo, one of the longest GH secretagogue trials ever conducted.
Improved lean mass and GH levels in post-menopausal women. A 12-month RCT in post-menopausal women confirmed MK-677 raised GH and IGF-1 to levels comparable to younger adults, with improvements in lean mass and functional strength measures, expanding the evidence base beyond older men.
Significant improvement in REM sleep architecture. A controlled trial documented MK-677 significantly improved REM sleep duration and quality, an effect attributed to GH's role in sleep architecture regulation. This sleep benefit is frequently cited as one of the most consistently reported subjective effects.
Reduced muscle wasting and improved rehabilitation outcomes. In hip fracture patients at high risk for muscle wasting, MK-677 significantly reduced nitrogen wasting and improved functional recovery measures, validating the anti-catabolic mechanism in a clinical population.
02, Mechanism of Action
MK-677 mimics ghrelin, the hunger hormone, at the pituitary gland, stimulating pulsatile GH release through a different pathway than GHRH analogues like tesamorelin or CJC-1295.
MK-677 binds the growth hormone secretagogue receptor (GHSR-1a), the same receptor activated by endogenous ghrelin. This drives GH release from the pituitary through a pathway independent of GHRH, meaning it can be combined with GHRH analogues for synergistic GH pulse amplification.
Like tesamorelin, MK-677 preserves pulsatile GH release rather than producing continuous elevation. The 24-hour half-life means once-daily dosing produces a sustained elevation of GH pulse amplitude rather than a single large spike.
GH stimulated by MK-677 drives hepatic IGF-1 production, the primary anabolic mediator responsible for muscle protein synthesis, bone formation, and tissue maintenance. IGF-1 typically rises 40–80% above baseline at therapeutic doses.
Because MK-677 works through the ghrelin receptor, it activates ghrelin's appetite-stimulating effects alongside GH release. Increased appetite is a consistent and well-documented side effect that users should anticipate and manage through dietary discipline.
MK-677 works through the pituitary's ghrelin receptor rather than bypassing GH regulation entirely. The normal somatostatin feedback still functions, preventing runaway GH elevation and maintaining physiological regulation, unlike direct GH administration.
The oral route is MK-677's defining advantage, no reconstitution, no injections, no cold chain. The trade-off is appetite stimulation (from the ghrelin mechanism) and water retention, which injectable GHRH + GHRP combinations produce less of. For users who want GH axis support without injections, MK-677 is the only meaningful option. For users comfortable with injection and wanting body composition optimisation, Ipamorelin + CJC-1295 gives more precise control.
03, Dosing Protocols
MK-677 has a well-established oral dosing protocol. The appetite side effect is dose-dependent and manageable at lower doses.
| Protocol | Dose | Frequency | Duration | Notes |
|---|---|---|---|---|
| Standard dose | 25 mg | Once daily, evening | 8–12 weeks | Most studied dose. Evening dosing aligns GH pulse with sleep, maximising sleep quality benefit. |
| Lower / tolerance dose | 10–15 mg | Once daily | 4 weeks then reassess | Reduces appetite stimulation and water retention while maintaining meaningful IGF-1 elevation. |
| Higher dose | 50 mg | Once daily | Not recommended long-term | Diminishing returns above 25mg with increased side effects. Used in some clinical trials. |
| Longevity maintenance | 10–25 mg | 5 days on / 2 off | Ongoing | Cycling to allow GH axis variability. Common in longevity protocols alongside other compounds. |
Appetite stimulation is significant, users without dietary discipline may gain fat alongside lean mass. Water retention is common in the first 2–4 weeks and typically resolves. Blood glucose monitoring recommended in pre-diabetic individuals as GH elevation can cause transient insulin resistance. Not recommended in active malignancy. IGF-1 monitoring every 8–12 weeks in long-term use.
04, Community Experiences
MK-677 has one of the largest communities of any compound in the GH space, driven by its oral convenience and the bodybuilding/fitness crossover audience. Discussion spans r/PEDs, r/bodybuilding, r/longevity, and r/Peptides. Key themes: sleep quality improvement is the most universally reported benefit and often surprises users who came for body composition; the appetite increase requires active management; and the longevity community increasingly uses it at lower doses as a maintenance compound rather than the higher doses used in bodybuilding contexts.
These are user-reported experiences from public forums. Not endorsed by Whats That Peptide and should not be interpreted as clinical evidence. Individual results vary. Always consult a healthcare professional.
"Lean mass up 4kg. IGF-1 from 140 to 230. Sleep is dramatically better, this surprised me most. The appetite is real and you have to manage it actively. If you don't track food you will gain fat alongside the muscle..."
"Using 10mg instead of 25mg. IGF-1 elevated to optimal range without the aggressive appetite. Sleep benefit is the same. No water retention at this dose. This is a maintenance compound for me, not a bulking tool..."
"The hunger is relentless. Eating at a deficit while on MK-677 requires serious discipline. Some people time the dose to coincide with their eating window if doing intermittent fasting, this helped me somewhat..."
"Different tools. MK-677: convenient, oral, more water retention, appetite increase, proven 2-year safety data. Ipamorelin/CJC: injectable, cleaner GH pulse, less water retention, better for body composition. I've run both. Both work. MK-677 if you hate needles..."