THE 30-SECOND OVERVIEW
At a glance
Most writing about MK-677 side effects is either a list with no sources or a forum consensus. The compound deserves better, because it has something almost no research compound has: placebo-controlled trials that measured adverse outcomes in hundreds of people over months and years, and reported them. This article goes through what those trials recorded, in the order the findings appeared. It describes study results. It is not guidance for use.
The compound and the mechanism behind the findings
MK-677, ibutamoren, is an orally active small molecule that mimics ghrelin at the receptor GHS-R1a. Ghrelin does two things that matter here: it drives growth hormone release, and it drives appetite. Growth hormone in turn raises IGF-1 and opposes insulin. Nearly every adverse finding in the trials traces to one of those three facts. We stock the compound as an oral liquid and as tablets, for research use only.
Glucose and insulin
This is the most consistent finding in the record.
Chapman and colleagues (1996), in the first dose-ranging study, saw fasting glucose rise from 5.4 to 6.8 millimoles per litre after four weeks of 25mg daily in healthy adults aged 64 to 81.
Svensson and colleagues (1998) found fasting glucose and insulin unchanged after eight weeks of 25mg in obese men, but an oral glucose tolerance test showed impaired glucose handling at both two and eight weeks.
Nass and colleagues (2008), over two years in 65 healthy older adults, reported fasting glucose up by an average of 0.3 millimoles per litre, about 5 milligrams per decilitre, and a decrease in insulin sensitivity.
Codner and colleagues (2001) saw no change in glucose or insulin in children over seven to eight days, which is short exposure and a different population.
The pattern is a modest but repeatable shift toward higher glucose and lower insulin sensitivity with sustained dosing, consistent with what elevated growth hormone does. Notably, the hip-fracture trials excluded patients with diabetes at entry (Bach et al., 2004), which is a signal of how the investigators read this risk.
Appetite and weight
The ghrelin receptor is the hunger receptor, and the trials saw it. Nass listed an increase in appetite as the most frequent side effect, adding that it subsided after a few months. Body weight in that study rose 2.7kg on MK-677 against 0.8kg on placebo, and while fat-free mass accounted for part of the difference, limb fat also rose more on the drug, 1.1kg against 0.24kg. Svensson recorded a transient rise in leptin in obese men (1999) alongside an unchanged total fat mass.
Fluid retention and muscle pain
Nass reported transient, mild lower-extremity oedema and muscle pain among the most frequent side effects over two years. Both are recognised effects of raised growth hormone and IGF-1, and both were described as transient in that study.
Cortisol and prolactin
The picture here is mixed across studies, which is itself the finding.
Chapman (1996) saw no change in cortisol and a 23 percent rise in prolactin that stayed within the normal range. Copinschi (1996), measuring 24-hour cortisol profiles and urinary free cortisol in young men over seven days, found no effect apart from a shift in the timing of the nocturnal nadir and morning rise. Svensson (1998) saw prolactin rise after the first dose and the peak not persist by two and eight weeks, with cortisol not increased at those points. Murphy (1998) found neither cortisol nor prolactin significantly higher after seven days.
Over two years, though, Nass recorded a cortisol increase of 47 nanomoles per litre, about 1.7 micrograms per decilitre. Short studies and long studies disagree, and the long study is the one that matters for sustained exposure.
The cardiac signal
Adunsky and colleagues (2010) stopped their 123-patient hip-fracture trial early because of a congestive heart failure signal in a limited number of patients receiving 25mg daily, and concluded that the compound had an unfavourable safety profile in that population. Those patients were elderly, recovering from major surgery, and the earlier hip-fracture study by Bach had already excluded anyone with heart failure at entry. The signal has not been reported in the younger or healthier cohorts, and the two-year Nass study described the drug as generally well tolerated. It remains the most serious adverse finding in the record, and it belongs in any honest account.
What the trials did not find
The 563-patient Alzheimer's trial (Sevigny et al., 2008) and the haemodialysis crossover (Campbell et al., 2018) reported no serious adverse effects attributable to the drug in their populations, and the dialysis authors described adverse effects as minimal. Lipid findings ran, if anything, the other way: Nass reported a fall in LDL cholesterol, and Svensson's lipoprotein paper (1999) found changes in several lipoproteins with no change in lipoprotein(a).
Bone marker studies (Murphy et al., 1999) recorded increased markers of both formation and resorption, and Nass recorded bone density changes consistent with increased remodelling. Whether that nets out as gain or loss over longer exposure is not established.
What the record does not cover
The trials are almost entirely adults over 60, obese men, patients, and children. Healthy young adults appear only in seven-day crossovers. The longest exposure is two years in 65 people. Anything about longer use, higher amounts than 25mg, or populations the trials did not enrol is not in the published record, and forum reports are not a substitute for it. Our MK-677 clinical trials article lists every study and what it measured; the dosage research article covers the amounts and durations behind these findings.
The takeaway
The MK-677 trials recorded a consistent metabolic cost, higher fasting glucose and lower insulin sensitivity; an appetite increase that faded; transient oedema and muscle pain; a cortisol rise that appeared only with long exposure; and one early trial termination over heart failure in elderly surgical patients. They also recorded no serious drug-attributed events in several other populations. That is a real safety record, with real limits, and it is more than most compounds in this catalogue can offer.
All products are intended for research use only. Not for human consumption. Must be 21 years of age or older to purchase.
References
1. Chapman, I. M., Bach, M. A., Van Cauter, E., et al. (1996). Stimulation of the growth hormone (GH)-insulin-like growth factor I axis by daily oral administration of a GH secretogogue (MK-677) in healthy elderly subjects. Journal of Clinical Endocrinology and Metabolism, 81(12), 4249-4257.
2. Copinschi, G., Van Onderbergen, A., L'Hermite-Balériaux, M., et al. (1996). Effects of a 7-day treatment with a novel, orally active, growth hormone (GH) secretagogue, MK-677, on 24-hour GH profiles, insulin-like growth factor I, and adrenocortical function in normal young men. Journal of Clinical Endocrinology and Metabolism, 81(8), 2776-2782.
3. Murphy, M. G., Plunkett, L. M., Gertz, B. J., et al. (1998). MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism. Journal of Clinical Endocrinology and Metabolism, 83(2), 320-325.
4. Svensson, J., Lönn, L., Jansson, J. O., et al. (1998). Two-month treatment of obese subjects with the oral growth hormone (GH) secretagogue MK-677 increases GH secretion, fat-free mass, and energy expenditure. Journal of Clinical Endocrinology and Metabolism, 83(2), 362-369.
5. Svensson, J., Ohlsson, C., Jansson, J. O., et al. (1998). Treatment with the oral growth hormone secretagogue MK-677 increases markers of bone formation and bone resorption in obese young males. Journal of Bone and Mineral Research, 13(7), 1158-1166.
6. Svensson, J., Jansson, J. O., Ottosson, M., et al. (1999). Treatment of obese subjects with the oral growth hormone secretagogue MK-677 affects serum concentrations of several lipoproteins, but not lipoprotein(a). Journal of Clinical Endocrinology and Metabolism, 84(6), 2028-2033.
7. Svensson, J., Lönn, L., Jansson, J. O., et al. (1999). Discrepancy between serum leptin values and total body fat in response to the oral growth hormone secretagogue MK-677. Clinical Endocrinology, 50(4), 451-456.
8. Murphy, M. G., Bach, M. A., Plotkin, D., et al. (1999). Oral administration of the growth hormone secretagogue MK-677 increases markers of bone turnover in healthy and functionally impaired elderly adults. Journal of Bone and Mineral Research, 14(7), 1182-1188.
9. Codner, E., Cassorla, F., Tiulpakov, A. N., et al. (2001). Effects of oral administration of ibutamoren mesylate, a nonpeptide growth hormone secretagogue, on the growth hormone-insulin-like growth factor I axis in growth hormone-deficient children. Clinical Pharmacology and Therapeutics, 70(1), 91-98.
10. Bach, M. A., Rockwood, K., Zetterberg, C., et al. (2004). The effects of MK-0677, an oral growth hormone secretagogue, in patients with hip fracture. Journal of the American Geriatrics Society, 52(4), 516-523.
11. Nass, R., Pezzoli, S. S., Oliveri, M. C., et al. (2008). Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Annals of Internal Medicine, 149(9), 601-611.
12. Sevigny, J. J., Ryan, J. M., van Dyck, C. H., et al. (2008). Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial. Neurology, 71(21), 1702-1708.
13. Adunsky, A., Chandler, J., Heyden, N., et al. (2011). MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study. Archives of Gerontology and Geriatrics, 53(2), 183-189.
14. Campbell, G. A., Patrie, J. T., Gaylinn, B. D., Thorner, M. O., & Bolton, W. K. (2018). Oral ghrelin receptor agonist MK-0677 increases serum insulin-like growth factor 1 in hemodialysis patients: a randomized blinded study. Nephrology Dialysis Transplantation, 33(3), 523-530.
