MK-677 (Ibutamoren) is a non-peptide agonist of the ghrelin receptor that stimulates the secretion of growth hormone (GH) and insulin-like growth factor 1 (IGF-1). Scientific interest in MK-677 for osteoporosis arises from the anabolic effects of GH and IGF-1 on bone metabolism. Several small-scale, randomized controlled trials have evaluated MK-677 in elderly adults, including those with low bone mineral density (BMD). For example, a pivotal study by Nass et al. (2008, J Clin Endocrinol Metab) showed that daily use of MK-677 for 12 months increased serum IGF-1 to youthful levels and attenuated the age-related decline in fat-free mass. Other studies observed that MK-677 led to modest increases in markers of bone formation (such as osteocalcin) and a reduction in bone resorption markers (like N-telopeptide), suggesting a potential benefit for bone health.

However, increases in actual bone mineral density were not consistently significant, and the studies generally had short durations and small sample sizes. There is currently no large, long-term clinical trial demonstrating a reduction in fracture risk or substantial improvements in BMD in osteoporotic populations. MK-677 is not approved by regulatory bodies for osteoporosis treatment, and its use remains investigational. Thus, while there is a plausible scientific rationale and some early evidence, the overall strength of evidence supporting MK-677 for osteoporosis is weak to moderate (rated 2/5).