MK-677 (Ibutamoren) Compounding Pharmacy: 503A vs 503B, What Patients Need to Know

What is MK-677, and why does its status decide the pharmacy question?

MK-677 (ibutamoren mesylate) is an oral, non-peptide small molecule that stimulates growth hormone release by acting on the ghrelin receptor. It is not a peptide and not a SARM, though it is often sold alongside SARMs [6]. Merck first synthesized it in 1995 and development was discontinued in 1999. It is not an FDA-approved drug, it has no USP or National Formulary monograph, and it is not a component of any FDA-approved drug [6].

That shapes the compounding question: before the choice between a state-licensed pharmacy and an outsourcing facility matters, ibutamoren has to be a substance FDA allows either type of compounder to use, and FDA has placed it in the group it flags for significant safety risks [1][2][3].

How does a state-licensed pharmacy differ from an outsourcing facility?

FDA's page on pharmacy compounding says state-licensed pharmacies and physicians may use only bulk substances that meet one of three conditions: they comply with a USP or National Formulary monograph, they are components of an FDA-approved drug, or they appear on FDA's list of bulk substances that can be used in compounding. The substance must also come with a valid certificate of analysis and be made by an establishment registered with FDA [5].

An outsourcing facility is a large, registered compounder. FDA maintains a separate safety-risk listing of bulk substances for outsourcing facilities, and ibutamoren mesylate appears on it [1][2][3].

Whichever type of compounder is involved, the first question is whether the bulk substance is allowed at all [1][5].

Where does ibutamoren sit in FDA's compounding framework?

FDA added ibutamoren mesylate to the group of bulk substances that may present significant safety risks (category 2) on December 29, 2022 for outsourcing facilities and on September 29, 2023 for state-licensed pharmacies and physicians. It remains on both lists [1][2][3].

FDA's stated reason is cardiac: ibutamoren 'poses significant safety risks due to the potential for congestive heart failure in certain patients', and the agency cites a hip-fracture trial that was terminated early over a potential safety signal of congestive heart failure [1][2][3][4].

That placement matters. Under FDA's category 1 policy, the agency generally does not intend to act against state-licensed compounders that meet stated conditions. Ibutamoren is in category 2, which is outside that policy. FDA's page says it would consider taking action against a compounder using a category 2 substance under its general enforcement policies [5].

What did FDA's pharmacy advisers conclude?

On October 29, 2024 the Pharmacy Compounding Advisory Committee voted 1 yes, 13 no, 0 abstain against adding ibutamoren mesylate to the pharmacy bulks list, in line with FDA's own proposal; members cited fluid retention, congestive heart failure and hyperglycemia [7][6][5]. FDA's review of the nomination noted that one outsourcing facility had reported compounding a 25 mg ibutamoren capsule in 2019 and 2020, and none since [6].

Does the 2026 HHS peptide compounding policy cover MK-677?

No. The draft enforcement-discretion policy for compounded peptides, filed October 28, 2026 as Federal Register document 2026-22192 with publication scheduled for October 30, 2026, names six peptides: BPC-157, epitalon, KPV, MOTS-c, Semax and TB-500 [8][9]. MK-677 is not one of them, and it is not a peptide in the first place [6][8].

Compounded drugs are not FDA-approved, and FDA does not review their safety, effectiveness or quality before they are marketed [9].

What safety concerns put it in that category?

In the hip-fracture trial FDA cites, 123 patients aged 60 or older received MK-677 25 mg daily (62 patients) or placebo (61) for 24 weeks. The trial was stopped early: per FDA's summary, 4 patients (6.5%) on MK-677 developed congestive heart failure versus 1 (1.7%) on placebo. Systolic blood pressure rose 11.9 to 16.4 mmHg versus 2.3 to -2.3 mmHg on placebo, serious adverse events occurred in 24% versus 13%, and the authors concluded MK-0677 'has an unfavorable safety profile' in this population [4][6].

A second hip-fracture trial of 161 patients aged 65 and older ran for 6 months. Serious adverse events were 24% (20/84) versus 18% (14/77), thrombosis occurred in 4 versus 0 patients, blood glucose rose 8.0 mg/dL versus a fall of 1.6 mg/dL, HbA1c rose 0.7% versus 0.3%, and edema or fluid overload was reported in 16 versus 10 patients [10][6].

FDA's wider concern is class-wide: by raising growth hormone and IGF-1, the drug may carry the risks listed on FDA-approved growth hormone labels, including increased risk of neoplasm, glucose intolerance and diabetes, intracranial hypertension, fluid retention, hypoadrenalism, hypothyroidism, pancreatitis, and in children slipped capital femoral epiphysis and scoliosis progression [6].

Is there an approved dose or product standard to compound against?

There is no approved dose and no USP or National Formulary monograph for ibutamoren [6]. Trials used fixed oral doses from 2 mg to 50 mg a day, with 25 mg once daily in most adult trials, or 0.2 to 0.8 mg/kg a day in children, for up to two years. None of these is a recommended dose [6]. FDA's review found no human pharmacokinetic data beyond a statement that the drug has high oral bioavailability and that a single dose stays active for about 24 hours [6].

What if a product is sold anyway?

FDA's December 12, 2025 warning letter to a seller of products marketed as SARMs stated that ibutamoren is excluded from the dietary supplement definition: it was authorized for investigation as a new drug, substantial clinical investigations were instituted, and it was not marketed as a supplement or food before that. The letter also states that products marketed with drug claims are unapproved new drugs [11]. On September 23, 2025 FDA warned that a children's product, Agebox iKids Growth Day Formula, contained ibutamoren not listed on the label, and listed risks including increased appetite, water retention, fatigue, muscle pain, changes in glucose metabolism and insulin sensitivity, and a possible increased potential for congestive heart failure in certain individuals [12].

FDA had received three adverse-event reports for ibutamoren through October 1, 2023, including a 68-year-old man with a prior pulmonary embolism and cardiac stent who had a large intracranial infarct while taking it, with other medicines confounding the picture [6][13]. The clinical trial record is separate from that count: trials reported congestive heart failure, higher blood glucose and fluid retention [6][4]. Published case reports also describe liver enzyme elevation, hyperglycemia and abnormal lipids in men who were using SARMs at the same time, where the role of MK-677 cannot be separated from the other drugs [6][13].