Source comparison
Ibutamoren vs MK-677: Why Both Names Persist in Research Literature
The dual naming convention isn't arbitrary. It reflects the compound's development timeline and regulatory classification. MK-677 was the internal Merck designation during Phase II clinical trials in the mid-1990s. When the compound advanced to Phase III studi
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- The dual naming convention isn't arbitrary. It reflects the compound's development timeline and regulatory classification. MK-677 was the internal Merck designation during Phase II clinical trials in the mid-1990s. When the compound advanced to Phase III studies for indications including growth hormone deficiency and frailty in elderly populations, the World Health Organization assigned the International Nonproprietary Name 'ibutamoren' under the INN system that standardizes drug nomenclature globally. Regulatory submissions to the FDA and EMA used 'ibutamoren mesylate' as the formal drug name, while the research community continued using MK-677 as shorthand.
- Neither name is more 'correct' than the other. They reference the same molecular entity at different stages of development. Research suppliers typically list both names to avoid confusion, but the CAS Registry Number (159752-10-0) is the definitive identifier. If you're cross-referencing studies or verifying compound identity through analytical methods like HPLC-MS, the CAS number eliminates ambiguity entirely.
- One practical distinction: when ibutamoren appears in supplier catalogues without the MK-677 designation, verify the molecular weight (528.662 g/mol for the mesylate salt form) and request a certificate of analysis showing purity >98%. The mesylate salt is the stable, bioavailable form used in clinical research. Free-base ibutamoren exists but is rarely supplied due to poor solubility. At Real Peptides, we provide both names on product labels and COAs to match whichever term researchers are more familiar with, but the underlying compound remains identical across all batches.