Chapter 15 — Key Takeaways

Growth Hormone Secretagogues: CJC-1295, Ipamorelin, Tesamorelin, MK-677

The one-sentence version

These compounds really do raise growth hormone — the mechanism is not in dispute and one of them holds an approval that proves it — but "raises growth hormone" is a measurement, not an outcome, and in this entire class the outcome has been properly tested exactly twice.

The claims and where they landed

All ratings as of this writing (2026). Each attaches to a claim, never to a molecule.

Why four compounds acting on one axis land in three tiers:

• Tesamorelin ✅ — someone ran phase 3 trials with an objective endpoint in a defined population and a regulator agreed.
• MK-677 ⚠️ — real randomized human data showing a real compositional effect, undercut by an absent functional benefit, a documented insulin-resistance signal, and no approval.
• CJC-1295 + ipamorelin ⚠️→❌ — the surrogate is established and conceded; the outcome is untested. The split is the point.
• Sermorelin / GHRP-2 / GHRP-6 ❌ — mechanism real, outcome evidence absent, and absent for long enough that the absence is itself informative.

The nine sections in nine lines

15.1 The axis has an accelerator (GHRH), a brake (somatostatin), and a downstream messenger (IGF-1). GH is pulsatile, so a single random GH measurement is nearly uninterpretable; IGF-1 is the usable readout.

15.2 GHRH analogs act at the GHRH receptor. Sermorelin is unmodified GHRH(1-29); CJC-1295 adds peptidase-resistant substitutions and, in its DAC form, an albumin tether extending duration from minutes to days. "CJC-1295" names two different molecules in the consumer market.

15.3 Ghrelin mimetics act at GHS-R. GHRP-6 stimulates appetite and affects cortisol and prolactin; ipamorelin was designed to avoid those. Selectivity is a statement about receptors, not about safety.

15.4 MK-677 (ibutamoren) is not a peptide — an orally active, long-acting ghrelin receptor agonist. Reliably raises GH and IGF-1; documented signal for increased blood glucose and reduced insulin sensitivity. Not approved.

15.5 Tesamorelin is approved for one narrow indication. Its existence proves the mechanism is real; its narrowness proves a real mechanism does not license broad claims.

15.6 The pulsatility argument is real physiology, not marketing — and it faces three counter-arguments: feedback opposes you, extended duration is a different signal rather than a more natural one, and none of it establishes an outcome.

15.7 "It raises growth hormone" is a mechanism claim; "it will improve your recovery" is an outcome claim. Seven steps sit between them, and the evidence for most of this class stops at step three.

15.8 Compound by compound: nearly all raise GH/IGF-1; only two have human outcome trials; the compounds most used are the compounds least studied.

15.9 Four ratings, four different reasons — and none of them moved because of mechanism.

The seven steps, compressed

1  compound binds pituitary receptor            ESTABLISHED
2  GH released                                  ESTABLISHED
3  IGF-1 rises                                  ESTABLISHED
   ────────── surrogate above / outcome below ──────────
4  intended tissue change (not fluid)           PARTLY, COMPOUND-SPECIFIC
5  measurable body-composition change           MK-677, tesamorelin only
6  functional outcome a person would notice     NOT SHOWN, any compound here
7  benefit survives harms, over years           NOT STUDIED outside approved use

What you can now evaluate

• Whether a "low growth hormone" lab result means anything on its own — and what to ask for instead
• Which of two receptors a given secretagogue acts on, from its name and its family
• Whether a compound sold as "CJC-1295" is the DAC version or the short-acting fragment, and why the question is not pedantic
• Why "selective" and "safe" are different claims requiring different evidence
• Why an approval in one population is not a general endorsement of a molecule
• Whether a claim you are reading is at step 3 or step 6 of the diagram above
• Whether an increase in "lean mass" might be water
• Why the same rating system gives a ✅ and a ❌ to two compounds acting at the same receptor
• What a clinician adds that a forum structurally cannot: a glucose and insulin panel, a baseline, a longitudinal view, and a reason to look for the effects nobody feels

Key terms

GHRH · GHRH receptor · somatostatin · IGF-1 · pulsatile secretion · tonic stimulation · ghrelin · ghrelin receptor (GHS-R) · GHRP · selectivity · DAC · sermorelin · tesamorelin · ipamorelin · MK-677 / ibutamoren · visceral adipose tissue · HIV-associated lipodystrophy · negative feedback · downregulation · tachyphylaxis · surrogate endpoint

Three sentences to carry forward

1. The axis pushes back. Any successful elevation of GH raises IGF-1, which inhibits GH release and raises somatostatin — so "preserves your feedback loop" describes a loop that opposes you.
2. Continuous stimulation of a pulsatile axis can produce the opposite of the intended effect — not speculation, but the mechanism of an approved cancer drug class (Ch 3 §3.5).
3. The arrow from surrogate to outcome is a hypothesis, not an assumption (Ch 5 §5.6). When it was tested in this class over two years, the surrogate performed flawlessly and the outcome did not follow.

Next: Chapter 16 moves from growth to repair, where the evidence problem has a different shape — not a surrogate that moves without an outcome, but an animal literature so large and so consistent that it has been mistaken for a human one.