IGF-1: What the Number Tells You, and What It Doesn't

TL;DR

• IGF-1 is measured because GH is pulsatile - a single random GH draw cannot distinguish normal secretion from deficient.
• It is a liver output, not a pituitary one - anything that changes hepatic function moves it without the pituitary behaving differently.
• Nutrition, age, illness and assay all move it - energy restriction and low protein intake lower it, and different assays are not interchangeable.
• A moving marker is pharmacodynamic activity, not benefit - GH trials in healthy older adults engaged the axis, raised adverse effects, and established no functional gain.
• Higher is not a goal - UK Biobank cohorts link higher IGF-1 to modestly raised cancer risk, and mortality follows a U-shaped curve.
• Age-referencing is descriptive, not a target - a younger person's position on the reference range is not something to aim at.

Educational content, not medical advice. No doses or protocols appear.

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Why IGF-1 is measured at all: GH is pulsatile, IGF-1 is not

If you read that a growth-hormone-releasing peptide "raises IGF-1," the first useful question is not whether that is true. It is: why is IGF-1 the thing being reported, rather than growth hormone itself?

The answer is a practical measurement problem. Growth hormone is secreted from the pituitary in discrete pulses, with the largest bursts typically occurring during sleep and troughs between them in which circulating concentrations are very low. This is not noise around a stable value; it is the physiological pattern. Between pulses, a healthy person's GH concentration can be indistinguishable from that of someone with genuine deficiency.

IGF-1 behaves differently. It circulates bound to binding proteins, has a far longer effective presence in the bloodstream, and shows only minor fluctuation across a day. It is also not meaningfully shifted by whether you have eaten before the draw. That stability is what makes it usable.

This is why clinical endocrinology uses IGF-1 as the workhorse measure of GH status in most situations. It is not that IGF-1 is more interesting than GH. It is that IGF-1 can be measured once and mean something, and GH usually cannot.

What "pulsatile" means for a single blood draw

The consequence is specific and worth stating plainly: a single random GH measurement cannot distinguish normal from deficient, because a low value may simply mean the draw landed between pulses. Formal assessment of GH secretion in clinical practice therefore relies on dynamic testing - provoking a response and measuring what happens - not on a single resting sample.

IGF-1 sidesteps that problem by acting as an integrated signal: it reflects roughly the cumulative GH exposure over a preceding window rather than the instant at which the needle went in. That is a real analytical advantage, and it is the entire reason the marker occupies the place it does.

It is also the source of a persistent misreading. Because IGF-1 is stable and easy to measure, it gets treated as the outcome the whole system exists to produce. It is not. It is the most measurable point on a chain, which is a different thing. The chain itself is covered in more detail in our piece on the GH axis.

The GH → liver → IGF-1 axis in plain terms

The sequence, stripped of jargon:

1. The hypothalamus releases growth-hormone-releasing hormone (GHRH), which signals the pituitary. A separate signal, somatostatin, restrains it, and ghrelin-receptor signalling amplifies it. The interplay of these produces the pulsatile pattern.
2. The pituitary releases growth hormone in bursts.
3. Growth hormone acts on growth hormone receptors, most consequentially in the liver, which produces the majority of circulating IGF-1.
4. IGF-1 circulates bound to binding proteins - principally IGFBP-3 and an acid-labile subunit - and mediates many, though not all, of GH's downstream effects on tissue.
5. IGF-1 also feeds back on the hypothalamus and pituitary to restrain further GH release. The axis is self-limiting by design.

Two features of that description matter for how the marker should be read.

First, IGF-1 is downstream of the liver. It is not a direct pituitary output. Anything that changes hepatic function or hepatic responsiveness to GH will change IGF-1 without the pituitary having done anything differently.

Second, not all of GH's actions run through IGF-1. Growth hormone has direct effects on tissue - including on lipolysis and on insulin sensitivity - that are not mediated by circulating IGF-1. So IGF-1 is a partial readout even of GH's own biology, not a complete one.

The compounds discussed in this pillar act at different points on that chain. GHRH analogues such as sermorelin, CJC-1295 and tesamorelin act at step 1; ghrelin-receptor agonists such as ipamorelin and the orally active investigational compound MK-677 act on the amplifying arm. Recombinant human growth hormone bypasses the pituitary entirely and enters at step 3. Those are meaningfully different interventions with different regulatory status and different evidence, and we compare them directly in sermorelin, CJC-1295 and tesamorelin compared and in HGH versus GH-releasing peptides.

Regulatory status, stated inline as it should be: tesamorelin is FDA-approved - under the brand Egrifta, approved in 2010 - for the reduction of excess visceral abdominal fat in people with HIV-associated lipodystrophy, and for that indication only. Sermorelin was previously FDA-approved as Geref for a paediatric growth-hormone-deficiency indication and was withdrawn from the US market in 2008; it is not currently marketed as an FDA-approved product. CJC-1295, ipamorelin and MK-677 are investigational and not FDA-approved for any indication. Recombinant human growth hormone is FDA-approved for defined deficiency and specified clinical indications, and is not approved for age-related or performance use.

What moves IGF-1 besides GH: nutrition, liver function, age, illness, protein intake

This is the part that most often goes missing from the sentence "peptide X raises IGF-1." IGF-1 is not a dedicated GH meter. It responds to several inputs that have nothing to do with the pituitary.

Nutritional state. IGF-1 synthesis is suppressed by reduced nutrient intake. Energy restriction, fasting, and low protein intake are all associated with lower circulating IGF-1; restoring intake raises it. This is a well-characterised effect and it is not small. Someone in a substantial calorie deficit and someone eating at maintenance are not comparable on this marker.

Liver function. Because the liver is the dominant source of circulating IGF-1, hepatic disease lowers IGF-1 - sometimes markedly - while the pituitary continues to release GH normally or even excessively. In advanced liver disease the marker becomes an unreliable index of GH status entirely.

Age. IGF-1 rises through childhood, peaks around puberty, and declines progressively through adult life. This decline is a normal feature of human physiology, not in itself a pathology.

Acute and chronic illness. Critical illness, systemic inflammation, poorly controlled diabetes, hypothyroidism and renal disease all influence the axis or the binding proteins, and can move measured IGF-1 independently of GH secretion.

Assay and standardisation. IGF-1 results are method-dependent. Different assays and different laboratory reference populations are not interchangeable, and results from different platforms should not be compared as if they were the same measurement. This is a recognised, actively discussed problem in the clinical chemistry literature - not a technicality invented to be cautious.

The cumulative point: a change in IGF-1 between two draws has several candidate explanations before a compound is one of them. Attributing it to an intervention requires controlling for the others, which is what a trial does and a personal before-and-after does not. The general principles are covered in biomarker monitoring.

Why IGF-1 is age-referenced, and what that does and doesn't imply

Because IGF-1 declines predictably across adult life, laboratories report it against age-specific - and usually sex-specific - reference populations rather than a single adult band. A value is interpreted relative to what is typical for people of the same age and sex on that assay.

What this does imply: comparing a value to a general adult reference, or to a value from a different decade of life, is not meaningful. Age-referencing exists because the underlying physiology genuinely changes.

What this does not imply - and this is where the marker is most often misused - is that a younger person's reference position is a target. The observation that IGF-1 falls with age is descriptive. It does not establish that the decline causes the features of ageing, and it does not establish that reversing the number reverses anything else. That inference is an extrapolation, and it is exactly the extrapolation the next two sections address.

There is a further reason age-referencing should not be read as a scoreboard: the biology does not run in one direction. Sitting higher relative to an age-matched reference is not established to be better, and the trade-off literature discussed below suggests it is not a neutral position either.

What a change in IGF-1 is evidence of - and what it is not evidence of

A compound that reliably raises IGF-1 has demonstrated something real and non-trivial: it engages the axis. In drug development, that is called pharmacodynamic activity - evidence that the molecule reaches its target and produces a measurable biological response. It is a necessary early finding. Without it, there is nothing to test further.

It is also, on its own, one of the weakest forms of clinical evidence.

A marker moving is not an outcome

The distinction is between a surrogate marker and a clinical endpoint. A surrogate is something measurable that is presumed to track what you actually care about. A clinical endpoint is the thing you actually care about - strength, function, body composition, injury recurrence, quality of life, survival.

Surrogates fail regularly. The history of clinical medicine contains a long list of interventions that moved a marker convincingly and then failed, or harmed, when tested against outcomes. The relevant example in this field is close at hand: a systematic review of randomised trials of growth hormone in healthy older adults (Liu et al., Annals of Internal Medicine, 2007) found small changes in body composition, no established functional benefit, and increased rates of adverse effects including joint swelling, joint pain, carpal tunnel syndrome and a trend toward new diagnoses of diabetes or pre-diabetes. The axis was engaged. The outcomes did not follow. The review concluded GH could not be recommended as an anti-ageing therapy.

That is the cleanest available illustration of the principle, and it is drawn from the intervention that moves the axis hardest. Compounds that move it less directly do not get a stronger inference for free.

Read the table as a single argument: the further right you move, the less the marker carries you.

The trade-off literature: why "higher" is not the goal it is often assumed to be

The assumption embedded in most consumer discussion of this axis is that IGF-1 is a good thing and more of it is better. The literature does not support that shape.

At the high end. Acromegaly - chronic pathological GH and IGF-1 excess - is associated with increased morbidity and reduced life expectancy, with cardiovascular and neoplastic complications prominent among the causes. This is a disease state rather than a model of modest elevation, but it establishes the direction of the risk at the top of the range.

Large prospective cohorts point the same way at non-pathological concentrations. UK Biobank analyses of several hundred thousand participants found higher circulating IGF-1 associated with modestly increased risk of overall cancer and of several site-specific cancers, including breast, prostate and colorectal, with associations also reported for thyroid cancer, melanoma and multiple myeloma. These are observational cohort findings - associations, with the usual limits on causal interpretation - but they are large, consistent, and not easily dismissed.

At the low end. The picture is not simply "lower is safer." UK Biobank and EPIC-Heidelberg analyses describe a U-shaped relationship between IGF-1 and all-cause mortality: both the lowest and the highest concentrations are associated with worse outcomes than intermediate ones. Again, observational.

The genetic natural experiment. People with Laron syndrome - congenital growth hormone receptor deficiency, and therefore lifelong very low IGF-1 signalling - have been reported to have markedly reduced incidence of cancer and diabetes, alongside other health consequences including obesity. This is a small, well-studied cohort rather than a trial, and it should not be read as a recommendation about anything. It is cited here only because it is the strongest available evidence that IGF-1 signalling has costs as well as benefits, in the direction opposite to the popular assumption.

Put together: this is a trade-off axis, not a dial with a good end. Any framing that presents a rising IGF-1 as an unambiguous win is arguing against a substantial and internally consistent body of epidemiology. That is the honest state of the evidence, and it is why we do not publish target values or describe a marker moving as a result.

For the parallel question of how a different endocrine axis is reasoned about, and why the comparison is less symmetrical than it looks, see how the GH and testosterone axes differ.

Where Vivre Labs fits

Vivre Labs offers several of the GH-axis compounds discussed above, and the logic of this article is the logic we apply to them: a rising IGF-1 shows the axis is engaged, not that anything has improved, and higher is not the goal.

Start with a baseline. Before any GH-axis compound is discussed, a clinician will typically want a baseline IGF-1 on a known assay, read against an age- and sex-matched reference, alongside glucose markers and your cancer history and screening status. Our baseline biomarker panel sets out what is typically measured, and peptide therapy monitoring panels explains what follow-up monitoring involves. A baseline that shows nothing to address is a legitimate result, not a failed consult.

• CJC-1295: a GHRH analogue. Investigational and not FDA-approved; small, short human pharmacology studies show raised GH and IGF-1, which is pharmacodynamic activity rather than demonstrated benefit.
• Ipamorelin: a selective ghrelin-receptor agonist. Investigational and not FDA-approved; small human pharmacology studies show GH release.
• Sermorelin: a shorter-acting GHRH analogue. Its previously approved US product was discontinued in 2008 for reasons other than safety; it is not currently marketed as an FDA-approved product.
• Tesamorelin: FDA-approved for reducing excess abdominal fat in adults with HIV-associated lipodystrophy, and for that indication only; any other use is off-label. Its label calls for IGF-1 monitoring during therapy.
• Lean mass and sleep quality protocol: pairs CJC-1295 and ipamorelin, both investigational. The name describes what people are seeking, not an established outcome.

Each compound page sets out its evidence tier and regulatory status, and the GHRH options are compared in sermorelin vs CJC-1295 vs tesamorelin.

Frequently asked questions

Why is IGF-1 measured instead of growth hormone? Because growth hormone is secreted in pulses, so a single random GH sample cannot distinguish normal secretion from deficient secretion - a low value may simply mean the draw landed between bursts. IGF-1 circulates bound to binding proteins, varies only minimally across a day, and is not meaningfully affected by recent food intake, so a single measurement carries interpretable information about cumulative GH exposure. Formal assessment of GH secretion itself relies on dynamic testing rather than a resting sample.

If a peptide raises my IGF-1, does that mean it is working? It means it engaged the axis - pharmacodynamic activity, which is a real finding and an early one. It does not establish that anything you care about improved. The distinction between a surrogate marker moving and a clinical endpoint improving is the central point of this article, and the systematic review of growth hormone in healthy older adults is the clearest illustration: the axis moved, adverse effects increased, and functional benefit was not established.

What is a good IGF-1 number? We do not publish target values, reference ranges or "optimal" bands, and the reason is evidential rather than cautious. IGF-1 is age- and sex-referenced, assay-dependent, and shifted by nutrition, liver function and illness - so a number without that context does not mean much. More fundamentally, the cohort literature describes a U-shaped relationship with mortality and positive associations between higher IGF-1 and several cancers, which means "higher" is not a defensible goal. Interpretation belongs with a clinician who has your history and knows which assay produced the result.

Are GH-releasing peptides approved? It depends entirely on which compound and which indication. Tesamorelin is FDA-approved for reduction of excess visceral abdominal fat in HIV-associated lipodystrophy, and for that indication only. Sermorelin was previously FDA-approved for a paediatric indication and was withdrawn from the US market in 2008. CJC-1295, ipamorelin and MK-677 are investigational and not FDA-approved for any indication. "Reviewed," "compounded" and "widely used" are not synonyms for approved, and any use is physician-directed and subject to local regulatory requirements.

Related reading

• Growth hormone and cancer risk: what the observational data shows - why IGF-1 is the marker the safety question is asked about, and what monitoring it does and does not tell you

• The GH axis: GHRH, the pituitary and IGF-1
• HGH versus GH-releasing peptides
• Sermorelin, CJC-1295 and tesamorelin compared
• Biomarker monitoring: what is measured and why

Part of The Complete Guide to Growth Hormone Peptides

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This article is educational and does not constitute medical advice. It deliberately contains no reference ranges, target values, thresholds, doses or protocols. CJC-1295, ipamorelin and MK-677 are investigational and not FDA-approved; tesamorelin is FDA-approved only for reduction of excess visceral abdominal fat in HIV-associated lipodystrophy; sermorelin's prior US approval was withdrawn in 2008. Regulatory status varies by country and any use should be physician-directed. Laboratory results should be interpreted by a qualified clinician with access to your history and to the assay used. Claims for the Malaysian market are subject to MAB requirements.

References

• Mayo Clinic Laboratories, "Insulin-Like Growth Factor 1, Serum" test overview; and Medscape, "Growth Hormone: Reference Range, Interpretation, Collection and Panels." (GH pulsatility; IGF-1 stability across the day; age- and sex-specific referencing; suppression of IGF-1 by reduced nutrient intake and liver disease.)
• "Challenges of insulin-like growth factor-1 testing." Critical Reviews in Clinical Laboratory Sciences, 2024. (Assay method-dependence and standardisation.)
• "Interpreting growth hormone and IGF-I results using modern assays and reference ranges for the monitoring of treatment effectiveness in acromegaly." Frontiers in Endocrinology, 2023.
• Liu H, Bravata DM, Olkin I, et al. "Systematic Review: The Safety and Efficacy of Growth Hormone in the Healthy Elderly." Annals of Internal Medicine, 2007;146(2):104–115. Systematic review of randomised controlled trials; small body-composition changes, increased adverse effects, not recommended as anti-ageing therapy.
• Knuppel A, Fensom GK, Watts EL, et al. "Circulating Insulin-like Growth Factor-I Concentrations and Risk of 30 Cancers: Prospective Analyses in UK Biobank." Cancer Research, 2020;80(18):4014–4021. Observational cohort.
• Murphy N, et al. "Circulating Insulin-Like Growth Factor-1 and Risk of Total and 19 Site-Specific Cancers: Cohort Study Analyses from the UK Biobank." Cancer Epidemiology, Biomarkers & Prevention, 2020;29(11):2332–2342. Observational cohort.
• "Association between circulating insulin-like growth factor 1 and risk of all-cause and cause-specific mortality." European Journal of Endocrinology, 2021;185(5):681. U-shaped association, observational cohort.
• "IGF-1 and Risk of Morbidity and Mortality From Cancer, Cardiovascular Diseases, and All Causes in EPIC-Heidelberg." Journal of Clinical Endocrinology & Metabolism, 2023;108(10):e1092. Observational cohort.
• Laron Z. "Growth hormone insensitivity syndrome (Laron syndrome): main characteristics and effects of IGF1 treatment." (Congenital GH receptor deficiency; reported reductions in cancer and diabetes incidence alongside other health consequences.) Small observational cohort.
• US Food and Drug Administration, EGRIFTA (tesamorelin for injection) prescribing information; FDA approval of tesamorelin, November 2010, for reduction of excess visceral abdominal fat in HIV-infected patients with lipodystrophy.
• US Food and Drug Administration, withdrawal of approval of Geref (sermorelin acetate) applications, 2008–2009; FDA subsequently determined the products were not withdrawn for reasons of safety or effectiveness.