Source comparison
Secretagogue vs Exogenous HGH: Why the Distinction Matters
A recurring source of confusion is the assumption that MK-677 “is” growth hormone or a growth-hormone injection. It is neither. MK-677 is a secretagogue — a compound that stimulates a gland to secrete its own hormone. The GH that appears in the bloodstream aft
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- A recurring source of confusion is the assumption that MK-677 “is” growth hormone or a growth-hormone injection. It is neither. MK-677 is a secretagogue — a compound that stimulates a gland to secrete its own hormone. The GH that appears in the bloodstream after MK-677 is the person’s (or research subject’s) own pituitary GH, released in amplified pulses. Recombinant HGH, by contrast, is the finished hormone administered directly, bypassing the pituitary and its feedback controls entirely.
- The distinction carries several practical consequences that the literature illustrates:
- Source of circulating GH
- The subject’s own pituitary
- Externally manufactured hormone
- Secretion pattern
- Amplified natural pulses[5]
- Non-pulsatile, dose imposed externally
- Feedback loop
- Partially preserved (IGF-1/somatostatin still act)
- Largely bypassed
- Route
- Oral
- Subcutaneous injection
- Regulatory status
- Investigational; never approved
- FDA-approved for specific deficiency indications
- One important corollary: because MK-677 depends on a functioning pituitary, its effect is fundamentally capped by the somatotroph’s capacity to respond. A person with an intact GH axis has a ceiling on how much GH the receptor amplification can produce. This is a mechanistic reason secretagogues are conceptually distinct from simply adding more hormone, and it is central to why they were studied as potentially “gentler” tools — a hypothesis that, as later sections show, did not automatically translate into a favorable clinical benefit-risk balance.