GH / IGF-1 axis
One of 6 mechanistic pathways to 💪 Build muscle & strength · 16 options
Growth hormone drives IGF-1, and IGF-1 activates PI3K/Akt/mTOR — the central hypertrophy signal. The honest read: GH is excellent for connective tissue, recovery and body composition, and a weaker direct hypertrophic agent than its reputation. Most of what people attribute to it is fluid and glycogen.
IGF-1 is the only honest read on whether a GH protocol is doing anything — GH itself is pulsatile and a single draw is close to meaningless. Track fasting glucose and insulin alongside, because the most predictable cost of this pathway is insulin resistance and it arrives quietly.
IGF-1 (Insulin-like Growth Factor 1)Growth Hormone, SerumFasting InsulinHbA1c (Hemoglobin A1c)🌙 Running GH Peptides or MK-677 covers these in one panel →
What engages this pathway
Ordered by how directly each one acts on the mechanism above — never by how much trial evidence exists. Each links to its full breakdown with dosing, half-life and vendor.
💉 HGH
Exogenous GH. Raises IGF-1 and lean mass reliably, improves recovery and connective-tissue quality — and much of the early scale change is water. Insulin resistance and carpal tunnel are dose-dependent and predictable.
💉 CJC-1295 W/ Dac
The DAC binds albumin and extends half-life to about a week, producing a sustained GH elevation rather than pulses. Sustained is not physiological, which is the trade — better IGF-1 area under the curve, more desensitization risk.
💉 CJC-1295 No Dac
Same GHRH backbone without albumin binding, so you get a clean pulse that respects somatostatin feedback. The more physiological choice.
💉 Ipamorelin
Ghrelin-receptor agonist that triggers GH release with unusually little cortisol or prolactin. The selectivity is the entire reason it displaced GHRP-6 in practice.
💉 CJC No Dac/Ipamorelin
GHRH plus secretagogue hit two different receptors on the somatotroph simultaneously. The combined pulse is larger than the sum, which is real synergy and the standard stack for a reason.
💉 GHRP-2
A potent secretagogue with a moderate prolactin and cortisol rise attached. More GH than ipamorelin, less clean.
💉 GHRP-6
The strongest appetite stimulus of the secretagogues — useful in a bulk, disqualifying in a cut.
💉 Hexarelin
The most potent GH release of the group, with the fastest desensitization. Short cycles only, and it has cardioprotective effects independent of GH that are interesting on their own.
💉 Sermorelin
GHRH 1-29, the shortest active fragment. Gentle, physiological, and the safest entry point into this pathway.
💉 MK-677
Oral, non-peptide, 24-hour GH and IGF-1 elevation. Lean mass rises consistently in trials — as does appetite, fasting glucose and fluid retention. A bulking tool that is honest about being one.
💉 MK-777
Described as an orally active non-peptide agonist at the same ghrelin receptor MK-677 hits, which would put it in the same GH-pulse-then-IGF-1 chain. Read that as a class assignment rather than a measured profile — there is no published human characterization of this molecule, so what is in a vial labeled MK-777 is an open question before the mechanism is.
💉 IGF-LR3
Long-arg-3 IGF-1 resists binding proteins, so far more free IGF-1 reaches the receptor. Systemically active, which is both why it works and why the hypoglycemia and unrestricted-growth concerns are legitimate.
💉 IGF-1 DES
A truncated IGF-1 with very short local action — the argument is site-specific hypertrophy at the trained muscle without systemic IGF-1 elevation.
💉 Increlex
Recombinant IGF-1 itself, so the entire secretagogue ladder above it is skipped along with the liver's regulatory step and the negative feedback that comes with it. The trial data sits in severe primary IGF-1 deficiency, which is what it is approved for; used for body composition it carries the hypoglycemia that the feedback loop normally prevents.
💉 MGF
Mechano-growth factor, the splice variant expressed by muscle after mechanical damage. It activates satellite cells; the native peptide's half-life is measured in minutes, which is the practical problem.
💉 PEG-MGF
PEGylation extends MGF's half-life from minutes to hours, which is the only way the mechanism gets a chance to matter systemically.
What actually decides this outcome, in order of size
Every agent on this page raises the same number, and the number is not the thing anybody wants. Ranked by how much of the outcome each one owns:
- What growth hormone is actually good at, which is connective tissue, body composition and recovery rather than force production. The secretagogue and releasing-hormone literature in normal aging was summarized with a title that is also its conclusion Hersch 2008, and the clinical picture has been updated since Fernandez-Garza 2025. The umbrella review of performance-enhancing drugs in healthy athletes is the calibration document for what this class does to performance rather than to appearance Warrier 2023.
- How much of an early change is water and glycogen. Growth hormone causes sodium and water retention, and glycogen carries water with it. A scale that moves in the first fortnight of any agent here has measured a compartment shift. That is not a criticism of the class; it is the reason the read-out below is not a scale.
- Pulse versus plateau, because the receptor cares. A releasing-hormone analog produces a pulse that respects somatostatin feedback; an albumin-bound version produces a sustained elevation that does not. Growth hormone releasing peptide-6 requires endogenous releasing hormone to work fully Pandya 1998, oral administration of a releasing peptide stimulates secretion in normal subjects Hartman 1992, and the pharmacokinetics of the peptide itself have been characterized in healthy volunteers Cabrales 2013. Sustained is not more physiological; it is less.
- Selectivity, because the ghrelin receptor does more than one thing. GHRP-2 and hexarelin raise prolactin, ACTH and cortisol alongside growth hormone, and that has been measured against releasing hormone directly in man Arvat 1997. Ipamorelin displaced GHRP-6 in practice for exactly this reason, and the structural basis of ghrelin receptor signaling by ibutamoren is now described Liu 2021.
- Whether IGF-1 means what you think it means, which is the surrogate question in its clearest form. IGF-1 testing has documented challenges Huang 2024, growth hormone deficiency diagnosis has accuracy caveats and cut-off problems across the ages Yuen 2023, and the axis interacts with intra-portal insulin in a way that complicates the simple reading Yuen 2024. Serum IGF-1 is also lowered by protein restriction independently of growth hormone Fontana 2008, which means a diet change can move it more than a peptide does.
- Whether the indication resembles yours at all. The strongest modern data for a releasing-hormone analog in body composition is a meta-analysis of randomized trials in HIV-associated lipodystrophy Badran 2026. That is a specific population with a specific fat distribution problem, and a trained thirty-year-old is not in it.
The order to run these in, and what has to be true first
Establish the baseline, know what you are actually buying, and start at the physiological end. The order is set by feedback: an agent that respects the axis can be stopped cleanly, and one that overrides it cannot.
- Baseline bloods before any of it. IGF-1 (Insulin-like Growth Factor 1), HbA1c (Hemoglobin A1c) with Fasting Insulin, Comprehensive Metabolic Panel (CMP), Lipid Panel (Cholesterol, HDL, LDL, Triglycerides), TSH (Thyroid-Stimulating Hormone) with Free T4 (Thyroxine) and, in men over forty, PSA (Total + Free + % Free). IGF-1 is here as a baseline rather than a target, and its interpretation caveats are published Huang 2024.
- Sleep and training first, because the largest natural pulse of this axis is in slow-wave sleep. Recovery, sleep & the anabolic window between sessions and Sleep depth, slow-wave & recovery quality are where that is argued properly, and it costs nothing.
- Sermorelin as the entry point, because it is the shortest active releasing-hormone fragment and keeps feedback intact. Gentle and physiological is a real property here, not a marketing word: the pituitary can still refuse.
- CJC-1295 No Dac with Ipamorelin next, because two receptors on the same cell produce a larger pulse than either alone. That synergy is the reason this combination became standard, and the selectivity of the secretagogue half is what keeps prolactin and cortisol out of it Arvat 1997.
- GHRP-2, GHRP-6 and Hexarelin are more potent and less clean, in that order. The cortisol and prolactin rise is measured Arvat 1997, GHRP-6 drives appetite hardest, and hexarelin desensitizes fastest. Pharmacokinetic characterization exists for the class Cabrales 2013.
- CJC-1295 W/ Dac and MK-677 trade pulse for area under the curve. A week-long albumin-bound elevation and a twenty-four-hour oral one are the same trade: better integrated exposure, more desensitization risk, and in the oral case appetite, fasting glucose and fluid retention all move together Liu 2021.
- HGH itself is a prescription and a different conversation. It bypasses the entire ladder above and the diagnostic question is whether there is deficiency at all, which has its own accuracy and cut-off literature Yuen 2023 Fernandez-Garza 2025.
- IGF-LR3, Increlex and MK-777 are last for three different reasons. The first two skip the liver's regulatory step and the negative feedback that comes with it, which is where the hypoglycemia risk comes from; the third has no published human characterization at all, so what is in a vial labeled that way is an open question before the mechanism is.
What gets bought for this that cannot move it
The category that fails structurally is anything sold on raising IGF-1. Every agent here raises it, which is why the number is quoted. What it predicts is the problem: testing has documented challenges Huang 2024, deficiency diagnosis has cut-off and accuracy caveats Yuen 2023, and the axis is modulated by portal insulin in ways that complicate the simple reading Yuen 2024. Meanwhile protein restriction alone lowers serum IGF-1 in humans Fontana 2008, so the same number is being moved by dinner. A rising IGF-1 proves exposure. It does not prove hypertrophy, and the athletic performance literature is where that distinction gets settled Warrier 2023.
The second failure is expecting force production. The honest summary of the secretagogue field in normal aging was written as a question about fountains and Tantalus Hersch 2008, and the modern clinical review does not overturn it Fernandez-Garza 2025. Lean mass and connective tissue respond; strength largely does not. Reading the body-composition data as strength data is the commonest disappointment on this page.
Two specific product misses. Bovine colostrum does not raise circulating IGF-1 in healthy adults, which was tested in short- and long-term administration studies Davison 2020, so an oral product claiming this axis has a published negative to answer. And a vial labeled MK-777 has no published human characterization at all: the class assignment is an inference from a related molecule, not a measured profile.
If the goal underneath is different, so is the page. If the target is androgenic signal, Androgen & anabolic-receptor signaling. If it is local repair after damage, Satellite cells & local repair. If it is visceral fat specifically, the releasing-hormone analog evidence sits in a defined clinical population Badran 2026 rather than in a general one. And if there is genuine growth hormone deficiency, that is an endocrinology diagnosis with a testing protocol Yuen 2023 rather than a peptide purchase.
How you would know it was working, on a real read-out and a real timescale
This page makes two predictions. IGF-1 (Insulin-like Growth Factor 1) rises on anything here that is genuinely being absorbed, and it rises whether or not anything you care about is changing Huang 2024; and HbA1c (Hemoglobin A1c) with Fasting Insulin drifts upward on sustained elevation, because growth hormone is diabetogenic and that is a dose-dependent, predictable consequence rather than a rare adverse event.
- IGF-1 (Insulin-like Growth Factor 1) at baseline and 6 weeks, same laboratory, and read as an exposure marker. Six weeks because hepatic IGF-1 output equilibrates to a changed growth hormone signal within a few weeks. Keep protein intake stable across the two draws, because restriction alone moves this number Fontana 2008.
- HbA1c (Hemoglobin A1c) with Fasting Insulin at baseline, 12 weeks and 6 months. Twelve weeks because glycated hemoglobin integrates over the red cell population, and this is the read-out on which the class trades its benefit.
- Comprehensive Metabolic Panel (CMP) at baseline and 3 months. Renal and hepatic function as context, and fasting glucose as the earlier version of the item above.
- Growth Hormone, Serum only in a diagnostic setting, never as a response marker. A random growth hormone level is close to uninterpretable because secretion is pulsatile, which is precisely why the diagnostic literature is about provocation tests and cut-offs Yuen 2023.
- A fixed strength test and a girth measurement monthly. This is where the class either delivers or does not, and it is the comparison the performance literature actually makes Warrier 2023.
What will fool you. Fluid retention and glycogen make the first three weeks look like hypertrophy on any scale and most impedance devices. Carpal tunnel symptoms and joint puffiness are dose signals rather than side effects to push through. Appetite from a ghrelin receptor agonist changes intake, which changes everything downstream Liu 2021. IGF-1 assays differ between laboratories enough to produce an apparent change that never happened Huang 2024. A secretagogue taken with food produces a smaller pulse, so a null result may be a timing result Hartman 1992. And an unlicensed vial has no assay behind the dose on its label.
Sources read for these sections
- Hersch EC. Growth hormone (GH)-releasing hormone and GH secretagogues in normal aging: Fountain of Youth or Pool of Tantalus?. Clinical Interventions in Aging 2008 · PMID 18488883
- Fernandez-Garza LE. Growth hormone and aging: a clinical review. Frontiers in Aging 2025 · PMID 40260058
- Warrier AA. Performance-Enhancing Drugs in Healthy Athletes: An Umbrella Review of Systematic Reviews and Meta-analyses. Sports Health 2023 · PMID 37688400
- Huang R, et al. Challenges of insulin-like growth factor-1 testing. Critical Reviews in Clinical Laboratory Sciences 2024 · PMID 38323343
- Yuen KCJ, et al. Diagnosis and testing for growth hormone deficiency (GHD) across the ages: a global view of the accuracy, caveats and cut-offs for diagnosis. Endocrine Connections 2023 · PMID 37052176
- Fontana L, et al. Long-term effects of calorie or protein restriction on serum IGF-1 and IGFBP-3 concentration in humans. Aging Cell 2008 · PMID 18843793
- Arvat E. Effects of GHRP-2 and hexarelin, two synthetic GH-releasing peptides, on GH, prolactin, ACTH and cortisol levels in man. Comparison with the effects of GHRH, TRH and hCRH.. Peptides 1997 · PMID 9285939
- Hartman ML. Oral administration of growth hormone (GH)-releasing peptide stimulates GH secretion in normal men.. J Clin Endocrinol Metab 1992 · PMID 1592884
- Cabrales A, Gil J, Fernandez E, Valenzuela C, Hernandez F, Garcia I, Hernandez A, Besada V, Reyes O, Padron G, et al. Pharmacokinetic study of Growth Hormone-Releasing Peptide 6 (GHRP-6) in nine male healthy volunteers. European Journal of Pharmaceutical Sciences 2013 · PMID 23099431
- Pandya N, et al. Growth hormone (GH)-releasing peptide-6 requires endogenous hypothalamic GH-releasing hormone for maximal GH stimulation. Journal of Clinical Endocrinology and Metabolism 1998 · PMID 9543138
- Liu H, et al. Structural basis of human ghrelin receptor signaling by ghrelin and the synthetic agonist ibutamoren. Nature Communications 2021 · PMID 34737341
- Yuen KCJ, et al. Growth hormone/insulin-like growth factor I axis in health and disease states: an update on the role of intra-portal insulin. Frontiers in Endocrinology 2024 · PMID 39665021
- Badran AS. Body composition, hepatic fat, metabolic, and safety outcomes of Tesamorelin, a GHRH analogue, in HIV-associated lipodystrophy: A meta-analysis of randomized controlled trials. Obesity Research and Clinical Practice 2026 · PMID 41545261
- Davison G. Oral bovine colostrum supplementation does not increase circulating insulin-like growth factor-1 concentration in healthy adults: results from short- and long-term administration studies. Eur J Nutr 2020 · PMID 31123862
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Frequently asked questions
Growth hormone drives IGF-1, and IGF-1 activates PI3K/Akt/mTOR — the central hypertrophy signal. The honest read: GH is excellent for connective tissue, recovery and body composition, and a weaker direct hypertrophic agent than its reputation. Most of what people attribute to it is fluid and glycogen.
16 options are mapped to this pathway in the Vault, including HGH, CJC-1295 W/ Dac, CJC-1295 No Dac, Ipamorelin. They are grouped by the mechanism they act through rather than ranked by how much trial evidence exists — 4 carry clinical validation and 12 are mechanistic predictions.
IGF-1 is the only honest read on whether a GH protocol is doing anything — GH itself is pulsatile and a single draw is close to meaningless. Track fasting glucose and insulin alongside, because the most predictable cost of this pathway is insulin resistance and it arrives quietly. The markers worth checking are IGF-1 (Insulin-like Growth Factor 1), Growth Hormone, Serum, Fasting Insulin, HbA1c (Hemoglobin A1c).
Unproven is not the same as ineffective. Of the 16 options on this pathway, 4 have clinical validation and 12 are graded theoretical — meaning the mechanism is sound but the specific human trial has not been run, which is true of a great deal of what works in this space. Nothing on this page is ordered by evidence tier, because sorting by trial count would bury the compounds you came looking for.
Where this goes next
Everything above is the free case for GH / IGF-1 axis. The protocol — the dosing, the order to correct things in, the week-by-week schedule and what to retest — is a lesson inside Skool.