MK-677

MK-677 (ibutamoren mesylate) is a non-peptide molecule that imitates the stomach hormone ghrelin. It activates the ghrelin receptor (GHSR-1a) on cells that control growth hormone release, so it turns up the body's own pulsatile GH output rather than supplying injected GH ¹¹. Structural studies have resolved ibutamoren inside the receptor's binding pocket ¹¹.

It was developed as an oral growth hormone secretagogue and has been studied in older adults, obese men, sleep trials, hip-fracture recovery, and pediatric growth hormone deficiency ¹⁰. In elderly adults, 2-9 weeks of daily oral dosing raised IGF-1 by 55-94% ¹⁷. The most-studied adult dose is 25 mg/day ²⁰.

No pharmaceutical approval exists in any jurisdiction. Development continues as LUM-201 in pediatric GH deficiency ⁷. Outside trials, MK-677 is sold online as a research chemical or mislabeled supplement. A multi-country European survey identified ibutamoren as the most frequently detected growth hormone secretagogue in seized products, many at active or overdosed levels ⁶. Mislabeled products have contained other drugs, including the anabolic steroid metandienone and undisclosed hormones ².

MK-677's primary action is activation of the ghrelin receptor (GHSR-1a). Ghrelin is a stomach hormone that normally signals hunger and triggers growth hormone release; MK-677 occupies the same receptor and keeps this pathway active ¹¹. Receptor-mapping work shows the GH-releasing effect depends on specific receptor sites and routes through a single receptor ¹¹.

Activation amplifies the pituitary's natural GH pulses instead of producing continuous GH exposure. That raises insulin-like growth factor 1 (IGF-1), the main growth signal that circulates in blood ²¹. A single 25 mg dose produced a peak GH of 55.9 µg/L in calorie-restricted volunteers, roughly six times the placebo level, and IGF-1 rose after 7 days of daily dosing ²¹. In older adults, daily oral treatment for 2-9 weeks raised IGF-1 by 55-94% ¹⁷.

Secondary effects appear through the same receptor and its brain circuits:

• Appetite: ghrelin-receptor signaling in the hypothalamus drives hunger; MK-677's orexigenic effect is strongest early in use ¹¹.
• Sleep: bedtime 25 mg increased slow-wave sleep about 50% and REM sleep more than 20% in young adults ¹⁶.
• Feedback braking: in rats, six weeks of daily dosing eliminated the acute GH response and increased hypothalamic somatostatin, a natural brake on the pathway ¹³.

Controlled human trials document effects primarily through GH/IGF-1 and metabolic readouts. The evidence for direct muscle or recovery benefits in healthy adults is much thinner ¹.

Human trial evidence

• GH and IGF-1: a single 25 mg dose raised peak GH to 55.9 µg/L versus about 9 µg/L for placebo, and IGF-1 increased from 186 to 264 ng/mL during a calorie-restriction trial ²¹. In elderly cohorts, IGF-1 rose 55-94% over 2-9 weeks ¹⁷.
• Nitrogen retention: a 7-day crossover trial shifted nitrogen balance to +0.31 g/day with MK-677 versus -1.48 g/day on placebo ²¹.
• Body composition: 25 mg/day for 8 weeks in obese men increased fat-free mass and energy expenditure ²⁰. Equivalent trials in lean, trained adults do not exist ¹.
• Sleep: 25 mg at bedtime increased stage IV sleep by about 50% and REM sleep by more than 20% in young adults; older adults had a roughly 50% REM increase ¹⁶.
• Bone turnover: formation and resorption markers rose in elderly adults across 2-9 weeks ¹⁷.
• Alzheimer's disease: a randomized trial found no clinical benefit on disease progression ¹⁵.

Case and market observations

• A 5-week use case with LGD-4033 added to MK-677 found lean mass gains but also a 15.4% fat mass gain, ALT up 205%, LDL up 40%, HDL down 36.4%, and free testosterone down 85.7% ⁹.
• Transaminitis after 2 months resolved after stopping ⁵.
• A spontaneous splenic rupture case involved MK-677 plus RAD-140; the link is speculative ³.
• Contaminated products have contained metandienone and undisclosed steroid hormones ².

Every published human protocol for MK-677 is oral, once daily. Studies used fixed doses of 5-50 mg/day without body-weight adjustment; 25 mg/day is the most-studied adult dose ¹⁷.

Published research schedules

Population	Dose and duration
Diet-induced catabolism	25 mg/day for 7 days 21
Obese men	25 mg/day for 8 weeks 20
Healthy elderly	10-25 mg/day for 2 weeks 17
Functionally impaired elderly	5/10/25 mg/day titrated to 25 mg/day for 9 weeks 17
Sleep quality	5 or 25 mg at bedtime for 7-14 days 16
Pediatric GH deficiency	single oral LUM-201 dose for GH-response testing 10

Community research pattern

Practitioner consensus commonly uses 10-12.5 mg/day for the first 1-2 weeks, then 20-25 mg/day for a total of 12-16 weeks, with 4-8 weeks off between cycles. Bedtime dosing aligns with the sleep-entrained GH rhythm and was used in sleep RCTs ¹⁶. Some community protocols use 5 days on and 2 days off, but this pattern has weaker support.

Trial durations were short: 7-14 days for sleep/catabolism studies, 8-9 weeks for body composition and bone-marker studies ¹⁶. No controlled trial has tested on/off cycling.

Formal drug-drug interaction studies for MK-677 are largely absent. The available evidence comes from RCT biomarker data and case reports.

• Alendronate: a postmenopausal osteoporosis trial combined the bisphosphonate alendronate with MK-677 and reported additive bone-turnover marker changes without an adverse interaction signal ¹⁷.
• Somatostatin analogs: these oppose GH release; in rats, MK-677 tachyphylaxis involved increased hypothalamic somatostatin tone ¹³, so this combination would be expected to blunt the GH response.
• Insulin or sulfonylureas: MK-677 biases toward reduced insulin sensitivity across trials ¹, so glycemic monitoring is the central consideration in the published assessments.
• SARMs: the only detailed human case combined LGD-4033 10 mg/day with MK-677 15 mg/day for 5 weeks. Lean mass and strength increased, but ALT rose 205%, LDL rose 40%, HDL fell 36.4%, and free testosterone fell 85.7% ⁹.
• GLP-1 receptor agonists: GHSR-driven appetite signaling would be expected to oppose GLP-1-mediated appetite suppression, but no human trial of this combination has been published.
• Mislabeled products: 'MK-677' capsules have contained metandienone, and other products carried undisclosed hormones that caused reversible gynecomastia and hypogonadism ².

GH-response attenuation with repeated dosing is measured, not just theoretical. A single 25 mg dose produced a 55.9 µg/L GH peak, but after 7 days of daily dosing the peak fell to 22.6 µg/L, while IGF-1 remained elevated ²¹. In rats, 6 weeks of daily dosing abolished the acute GH response and raised hypothalamic somatostatin, indicating increased inhibitory tone rather than receptor loss ¹³.

Published trials did not cycle MK-677; they administered it continuously once daily for days to months ¹⁵. Community research protocols instead use 12-16 weeks on with 4-8 weeks off, or an 8-12 week block. Off-periods are intended to allow metabolic and hormonal measures to normalize. In the combined LGD-4033/MK-677 case, liver enzymes, testosterone, triglycerides, and HDL returned toward pre-cycle values after stopping, though total cholesterol and LDL remained elevated ⁹.

No human study has tested whether intermittent schedules, such as 5 days on and 2 days off, prevent the attenuation seen in chronic rodent dosing.

Combination data are limited, but several pairings appear in the literature.

• With SARMs: the documented LGD-4033 + MK-677 case showed strength and lean mass gains alongside large metabolic and hormonal changes ⁹. A RAD-140/MK-677 case involved spontaneous splenic rupture, with a speculative link ³. Adulterated RAD-140/MK-677/cardarine products have caused gynecomastia and hypogonadism ⁸.
• With GHRH analogs such as CJC-1295: GH-releasing hormone receptor activation is a different receptor from GHSR-1a, so the two mechanisms are theoretically complementary. No clinical outcome trial of this stack exists.
• With GHRP-2, GHRP-6, or ipamorelin: these target the same ghrelin receptor as MK-677. Expected benefit is redundant, and chronic receptor-driven signaling is tied to the somatostatin brake seen in animal data ¹³.
• With BPC-157 or TB-500: no shared pathway or reported interaction appears in the available literature.
• With GLP-1 agonists: the appetite-increasing action of MK-677 would work against GLP-1 appetite suppression, with no trial evidence to quantify the net effect.

Multi-compound stacks also carry product-contamination risk. Several 'supplement' products have contained undisclosed anabolic or hormonal drugs ².

MK-677 has no FDA or EMA approval for any indication and is not a lawful dietary ingredient. It remains an investigational oral GH secretagogue, with development continuing as LUM-201 for pediatric growth hormone deficiency ⁷. The literature describes open online sale as unapproved distribution ¹.

Anti-doping: under WADA rules, growth hormone secretagogues are prohibited at all times, in and out of competition. Analytical methods detect ibutamoren in urine, dried blood spots, and hair ⁴. A single 10 mg dose produced a hair concentration of 1.3 pg/mg four weeks later; a 90-day regimen produced 224 pg/mg, so detection liability can persist after stopping ⁴.

Supply risk is substantial. A 5-year European survey found ibutamoren in seized products, frequently at active or overdosed doses ⁶. Finished products have contained metandienone as an undisclosed ingredient ², and other products carried undisclosed testosterone, estradiol, and GH associated with reversible gynecomastia and hypogonadism ⁸.

The side-effect profile comes mainly from short human trials, case reports, and market surveillance. No multi-year safety database exists for the community dose range ¹.

Common and metabolic effects

• Appetite increase: the most consistent effect, consistent with ghrelin-receptor activation ¹¹.
• Fluid retention and edema: recognized in case reporting and listed as a known side effect ⁵.
• Glucose and insulin: trials show a consistent bias toward reduced insulin sensitivity ¹. In obese men, triglycerides and HDL changed transiently in week 2 before the LDL/HDL ratio improved by week 8 ¹⁸.
• Testosterone: an 8-week trial in obese men found lower total testosterone versus placebo while the free androgen index remained stable ²⁰. In the combined LGD-4033 case, free testosterone fell 85.7% ⁹.
• Sleep changes: slow-wave and REM increases are usually described as improvements ¹⁶.

Serious and less common

• Hepatotoxicity: a man in his early 30s developed transaminitis after 2 months; liver tests normalized after stopping ⁵.
• Cardiovascular: MK-677 showed an unfavorable safety profile in patients with congestive heart failure ¹.
• Splenic rupture: one case with MK-677 plus RAD-140, with a speculative role for MK-677 ³.
• GH-response desensitization: in rats, 6 weeks of daily dosing eliminated the GH response ¹³.
• Contamination: products labeled as MK-677 have contained metandienone or undisclosed hormones, causing gynecomastia and hypogonadism ².

Long-term cancer, cardiovascular, and pediatric safety data remain open questions ¹.