MK-677 (Ibutamoren) + MOTS-c Stack: When to Pick One Over the Combination

What MK-677 (Ibutamoren) Actually Does

MK-677 is an oral, non-peptide small molecule, not a peptide and not a SARM. It stimulates growth hormone release by acting on the ghrelin receptor, which raises IGF-1 [4]. Merck first synthesized it in 1995 and discontinued development in 1999 [4]. It is not FDA-approved and is not a component of any approved drug [4].

Ibutamoren is also under study as LUM-201 in children with growth hormone deficiency. In a 6-month randomized placebo-controlled trial of 68 prepubertal children, FDA's review describes it as generally well tolerated, with increased appetite the most common drug-related event at 2.5 to 3 times the rate on placebo [4][10].

Adult trials used 2 mg to 50 mg a day, most often 25 mg once daily, for up to 2 years [4]. The benefits measured were narrow. In 65 healthy adults aged 60 to 81, 25 mg daily for a year added 1.1 kg of fat-free mass against a 0.5 kg loss on placebo, with no improvement in strength or function, a 2.7 kg versus 0.8 kg rise in body weight, and about a 5 mg/dL rise in fasting glucose [6]. In 563 people with mild to moderate Alzheimer's disease, IGF-1 rose 72.9% at 12 months and no progression measure changed; drug-related adverse events were 35.5% versus 23.9% on placebo, and glucose increases occurred in 15.4% versus 4.6% [7]. In 24 obese men, IGF-1 rose about 40% over 8 weeks and fat-free mass rose, while total and visceral fat did not change and an oral glucose tolerance test showed impaired glucose handling at 2 and 8 weeks [11].

The safety record is the other half of the picture. In FDA's summary of the 123-patient hip-fracture trial, congestive heart failure occurred in 4 patients (6.5%) taking MK-677 versus 1 (1.7%) taking placebo, systolic blood pressure rose 11.9 to 16.4 mmHg against 2.3 to -2.3 mmHg on placebo, serious adverse events occurred in 24% versus 13%, and glucose and HbA1c rose more; the trial was stopped early for that heart-failure signal [4][5]. The trial authors called the profile unfavorable in that population [5]. FDA's review adds that by raising GH and IGF-1, MK-677 may carry the risks listed on approved growth hormone labels: neoplasm, glucose intolerance and diabetes, intracranial hypertension, fluid retention, hypoadrenalism, hypothyroidism and pancreatitis, plus slipped capital femoral epiphysis and scoliosis progression in children [4].

What MOTS-c Is

MOTS-c is a 16-amino-acid peptide, molecular weight about 2174.6 g/mol, encoded in mitochondrial DNA and first reported in 2015 [1][2]. Its effects have been shown in cells and rodents. In mice, injected MOTS-c prevented age-dependent and high-fat-diet-induced insulin resistance and diet-induced obesity, with skeletal muscle as the main target and AMPK activation in the pathway [2]. At 0.5 mg/kg/day intraperitoneally it produced about 20% lower body weight than controls after 8 weeks on a high-fat diet, and a late-life schedule of 15 mg/kg three times weekly from 23.5 months of age lengthened median lifespan from 912 to 970 days [1][3].

Human MOTS-c research has measured the body's own peptide, not an injected product. Exercise raises endogenous MOTS-c expression in skeletal muscle and in circulation [3], though in 30 adults randomized to endurance exercise, resistance exercise or control, MOTS-c showed only a trend to increase after endurance exercise, and plasma levels did not track fitness, leg strength or muscle mitochondrial DNA copy number [12].

FDA's review raises two practical questions about an injected version: MOTS-c breaks down quickly in human blood in vitro, so it is unclear whether an injection could reach active levels, and injectable peptides carry an immunogenicity risk from aggregation and peptide-related impurities [1]. FDA also found no animal toxicity studies [1].

Could MOTS-c Offset MK-677's Glucose Effects?

MK-677's glucose effect has been measured repeatedly in people: fasting glucose up about 5 mg/dL over 12 months in healthy older adults [6], higher HbA1c increases (11.1% versus 1.4%) in the Alzheimer's trial [7], and impaired glucose handling on tolerance testing in obese men [11]. The insulin-sensitizing effect of MOTS-c comes from mice [2]. Because no human study of administered MOTS-c exists, there is no human evidence that adding it would offset MK-677's glucose effects [1].

When MK-677 Alone Might Be Chosen

MK-677 has human trials behind it, so it has something measurable to compare against, but what it measures is narrow. IGF-1 rose in each of these trials [13][6][14][7][11], and the functional results did not follow. In healthy older adults, fat-free mass rose about 1.1 kg over a year while strength and function did not improve [6]. In hip-fracture recovery, gait speed improved while most other functional measures did not [5], and in a separate 161-patient hip-fracture trial function did not improve significantly despite an 84% IGF-1 rise [14]. In mild to moderate Alzheimer's disease, a 72.9% IGF-1 rise produced no change on any progression measure [7]. The congestive heart failure signal and the blood pressure, glucose and HbA1c rises came from the hip-fracture trials [4][5][14].

MK-677 has been tested in combination with alendronate, not with MOTS-c. In 292 postmenopausal women with osteoporosis, adding MK-677 25 mg to alendronate 10 mg partly offset alendronate's fall in bone-turnover markers (osteocalcin -40% versus -54% with alendronate alone) and raised femoral neck bone density 4.2% versus 2.5%, with no extra gain at the spine, total hip or total body [13]. FDA's review reports no formal drug-interaction studies [4].

When MOTS-c Alone Gets Chosen Instead

Two considerations apply, and neither is an efficacy result.

The first is MK-677's glucose and fluid effects. MOTS-c has no human safety data, so avoiding those effects does not make it a safer option; its safety in humans is unknown [1].

The second is regulatory, and here the two compounds genuinely differ. MK-677 sits in FDA's category of bulk substances that may present significant safety risks when compounded, added December 29, 2022 for outsourcing facilities and September 29, 2023 for state-licensed pharmacies and physicians, with FDA citing the potential for congestive heart failure in certain patients [8][15][16]. In October 2024 FDA's Pharmacy Compounding Advisory Committee voted 1 yes to 13 no against adding ibutamoren to the list of bulk substances that can be used in compounding [17]. MOTS-c is listed in the withdrawn-nomination table, which is not a finding that it is safe [8]. FDA staff recommended against listing it in July 2026; the committee voted in favor the same month, a non-binding recommendation that does not put it on the list [1][18]. HHS's draft enforcement-discretion policy of October 2026 names MOTS-c acetate (subcutaneous or intramuscular injection) among six peptides for which HHS says it does not intend to take enforcement action against certain state-licensed pharmacies, federal facilities and licensed physicians when its conditions are met; it does not name MK-677, and the draft is not an approval and is not binding on HHS or the public [19][20].

Doses That Were Studied

For MK-677: 2 mg to 50 mg a day in trials, 25 mg once daily in most adult studies, for up to 2 years. There is no approved dose, and none of these figures is a recommendation [4]. For MOTS-c: the products nominated to FDA were 5 mg and 10 mg subcutaneous injections, and the rodent doses of 0.5 to 15 mg/kg cannot be converted into a human dose [1].

Status and Sport

FDA's December 12, 2025 warning letter states that ibutamoren is excluded from the dietary supplement definition and that products marketed with drug claims are unapproved new drugs [21]. In September 2025 FDA warned that a children's growth product contained ibutamoren not listed on the label, citing risks including increased appetite, water retention, fatigue, muscle pain, changes in glucose metabolism and insulin sensitivity, and a possible increase in congestive heart failure in certain individuals [22].

Both compounds are on WADA's Prohibited List at all times, in and out of competition: ibutamoren in S2.2.4 for growth hormone secretagogues and mimetics, and MOTS-c in S4.4.1 for AMPK activators [9]. Both appear on the 2026 List and in the 2027 tracked-changes version [9][23]. For competitive athletes, both are off-limits.