Ibutamoren / MK-677

What it is

Despite where it appears online, ibutamoren is not a peptide. It is the active small molecule; ibutamoren mesylate is its salt. FDA’s record connects it to MK-677, MK-0677, MK0677, and LUM-201.

It is not a peptide and not a selective androgen receptor modulator. The free active moiety and mesylate salt should not be silently collapsed, and a development code or ingredient name does not authenticate an online, compounded, mislabeled, or hidden-ingredient product.

Why people care

MK-677 is often discussed alongside peptides, SARMs, growth hormone, and recovery products. That grouping can obscure what it is and what its trials measured. Higher growth hormone, IGF-1, fat-free mass, or bone-turnover markers are not automatically strength, recovery, cognition, or anti-aging outcomes.

What humans actually show

• Healthy older adults: A two-year randomized placebo-controlled modified-crossover trial enrolled 65 healthy adults aged 60 to 81. MK-677 increased growth hormone, IGF-1, fat-free mass, body weight, and limb fat but did not improve strength or function; the authors reported that the study was underpowered to evaluate functional endpoints, so this is an unmet endpoint rather than a demonstrated absence of effect. Fasting glucose increased and insulin sensitivity decreased; common effects included increased appetite, transient lower-extremity edema, and muscle pain.
• Hip-fracture recovery: A randomized phase 2b trial enrolled 123 older adults recovering from hip fracture. IGF-1 increased, and one gait-speed analysis favored MK-0677, but stair-climbing power and most other functional measures did not improve. The trial stopped early after a congestive-heart-failure signal. FDA’s briefing reports four heart-failure events with ibutamoren and one with placebo; the paper describes an unfavorable safety profile in this population.
• Alzheimer disease: A 12-month randomized trial enrolled 563 people with mild to moderate Alzheimer disease. MK-677 increased serum IGF-1 but did not slow clinical progression.
• Ibutamoren with alendronate: A randomized study enrolled 292 postmenopausal women with low femoral-neck bone mineral density. The combination improved femoral-neck bone density more than alendronate alone but did not produce the same enhancement at the lumbar spine, total hip, or total body. It measured markers and bone density, not fracture reduction.

Mechanistic and nonhuman evidence

A seven-to-eight-day study in children with growth hormone deficiency documented short-term growth-hormone and IGF-1 responses. This is target-engagement evidence, not annualized height, final height, or long-term safety evidence, and it cannot substitute for the current phase 3 trial.

Structural and cell experiments resolved ibutamoren bound to the human ghrelin receptor and described nonpeptide agonist signaling. That work explains mechanism; it does not establish patient-important benefit, safety, or product identity.

FDA and U.S. status

FDA stated in September 2025 that ibutamoren is not approved and that its safety and efficacy have not been established. An exact-active-ingredient Drugs@FDA search returned no match in the dated source pass; the FDA statement—not the database non-match alone—supports the status boundary.

ClinicalTrials.gov lists a recruiting phase 3 LUM-201 study in pediatric growth hormone deficiency without posted results. A recruiting trial is not an approval or positive result.

FDA’s current compounding-risk page places ibutamoren mesylate in category 2 because of significant safety concerns, including possible congestive heart failure. In October 2024, the Pharmacy Compounding Advisory Committee voted 1 yes, 13 no, and 0 abstentions on placing it on the 503A Bulks List. The advisory vote and category placement are not a final rule, prescribing conclusion, or universal legal conclusion.

Risks and warning limits

FDA’s category-2 record identifies potential congestive heart failure as a significant safety risk. FDA’s September 2025 alert lists increased appetite, water retention, fatigue, muscle pain, altered glucose metabolism and insulin sensitivity, and possible increased heart-failure risk; it says long-term effects are unknown.

The healthy-older-adult trial recorded increased fasting glucose, reduced insulin sensitivity, increased appetite, edema, and muscle pain. The hip-fracture trial stopped early after the heart-failure signal. There is no FDA-approved prescribing information for ibutamoren, so these sources do not define a complete contraindication, adverse-event, or interaction profile.

What remains unknown

• The efficacy and benefit-to-risk balance of LUM-201 in the current phase 3 pediatric program.
• Long-term cardiovascular, metabolic, neoplastic, and other safety effects.
• A patient-important recovery, strength, sleep, cognition, or anti-aging benefit.
• Direct interaction safety outside the narrow alendronate trial.
• The identity, purity, concentration, and stability of an unspecified ibutamoren product.
• Any future final FDA compounding-list action.

Product identity and quality limits

Ibutamoren and ibutamoren mesylate are related active-moiety and salt terms, not automatically interchangeable product descriptions. MK-677, MK-0677, and LUM-201 are development names, not proof of formulation or approval.

FDA found undeclared ibutamoren in one specific product in 2025. That illustrates a product-identity problem; it does not establish the contents of every product using an MK-677 name. A ClinicalTrials.gov record for LUM-201 cannot authenticate an unrelated material.

What has been studied together

The alendronate trial is direct coadministration evidence in postmenopausal women. It measured bone markers and bone density, did not establish fracture reduction, and does not support other combinations.

FDA warns that ibutamoren may interact with medicines and products such as SARMs in potentially harmful ways. The focused search did not identify an adequate direct interaction program for SARMs, growth hormone, testosterone, peptides, glucose-lowering medicines, or multi-ingredient performance products. Missing evidence does not establish compatibility or safety.

What people are hearing

• “MK-677 is a peptide or SARM.” FDA describes ibutamoren mesylate as the salt of a nonpeptide small molecule; it is a ghrelin-receptor agonist and growth hormone secretagogue.
• “Higher GH or IGF-1 proves recovery or muscle benefit.” Trials show target engagement without consistent functional or disease outcomes.
• “A phase 3 trial means LUM-201 is approved.” The current recruiting trial has no posted results, and FDA states ibutamoren is not approved.
• “No prescription label means there are no known risks.” FDA and human trials record heart-failure, fluid-retention, and metabolic concerns.

Questions readers raise

Readers ask whether MK-677 is a peptide or SARM, whether higher IGF-1 proves recovery, and whether LUM-201’s phase 3 program changes current approval status. These are questions to investigate, not evidence of benefit or safety. PepCurrent has not published anecdotal theme counts or public user reviews for this profile.

What would change this answer

• Posted, independently interpretable phase 3 results with patient-important outcomes and a defined LUM-201 product.
• Replicated functional or disease benefits rather than endocrine target engagement alone.
• Longer-term cardiovascular and metabolic safety evidence.
• A new FDA approval, final compounding-list action, or other material official status change.
• Direct interaction evidence for defined products and combinations.

Sources and records

• FDA September 2025 ibutamoren hidden-ingredient alert
• FDA category-2 compounding-risk page
• FDA October 2024 PCAC briefing document
• FDA October 2024 PCAC transcript
• Drugs@FDA exact active-ingredient search
• Current LUM-201 phase 3 registry, NCT06948214
• Healthy older adults trial — PMID 18981485
• Hip-fracture trial — PMID 21067829
• Alzheimer trial — PMID 19015485
• Alendronate combination trial — PMID 11238495
• Short pediatric endocrine study — PMID 11452249
• Ghrelin-receptor structure study — PMID 34737341