IGF-1: A Literature Course in Six Modules

How this course is organised

This course walks through six modules, each summarising what a verified set of published papers actually reported about IGF-1 (insulin-like growth factor 1). Every module closes with a short statement of what that evidence cannot support. No dosing schedule appears anywhere on this page, because the verified papers used here do not report human dosing protocols for exogenous IGF-1. This page is for educational purposes only and is not medical advice; consult a licensed physician about any medical or health decision.

Module 1 — What IGF-1 Is and How It Has Been Studied

Definition and class

IGF-1 is a single-chain polypeptide hormone that belongs to the insulin ligand family, and researchers routinely study insulin and IGF-1 together as one signalling system, as in a review titled Insulin, IGF-1 and longevity. The family relationship is close enough that a 2025 Cell Reports study reported virally encoded insulin/IGF-like peptides that bind and inhibit IGF-1 receptor signalling, and reported that this inhibition enhanced viral replication (PMID 40829596).

Origin and regulation

IGF-1 is classically described as the downstream mediator of growth hormone (GH). In a clinical series of patients treated for acromegaly, researchers examined the correlation between GH and IGF-1 measurements during treatment and reported that the two markers were related but did not track one another perfectly in every patient (PMID 27858572). Circulating IGF-1 is not set by the pituitary alone: a review in Calcified Tissue International described evidence that the gut microbiota influences IGF-1 levels and the skeletal outcomes linked to them (PMID 29362822).

Forms encountered in the literature

• Endogenous IGF-1 — measured as a serum biomarker, for example in acromegaly follow-up (PMID 27858572).
• Recombinant human IGF-1 — the basis of an approved prescription product discussed in Module 6.
• Genetically reduced IGF-1 signalling — worm and other model-organism systems where the pathway is dialled down rather than a peptide administered (PMID 40852035).
• IGF-1 as a doping agent — reviewed alongside GH, insulin and erythropoietin in sports endocrinology (PMID 36736729).

Limits of the evidence in Module 1

The verified set contains no head-to-head characterisation of modified IGF-1 analogues, no structural comparison studies, and no human trial of exogenous IGF-1 in healthy adults. Statements about analogue variants circulating outside clinical use are therefore not supported by these papers and are not made here.

Module 2 — Mechanism as Described in the Literature

Receptor-level signalling

The pathway is described in these papers as ligand engagement of the IGF-1 receptor, a cell-surface receptor tyrosine kinase. The clearest receptor-level demonstration in the verified set is the 2025 report that viral insulin/IGF-like peptides inhibited IGF-1 receptor signalling, which the study linked to enhanced viral replication (PMID 40829596). That design is informative because it shows what happens when receptor signalling is blocked rather than amplified.

The insulin/IGF-1 signalling (IIS) axis in ageing biology

Much of the mechanistic literature on IGF-1 comes from ageing research, where reduced signalling — not added peptide — is the intervention. A review of insulin, IGF-1 and longevity described the conserved relationship between lowered IIS activity and extended lifespan across model organisms (PMID 22396862). A 2025 microPublication Biology report in C. elegans found that reduced insulin/IGF-1 signalling, combined with loss of pals-22, promoted silencing of repetitive DNA (PMID 40852035), placing the pathway upstream of chromatin-level effects rather than growth alone.

The relationship is also conditional. Researchers reported that the longevity effects of reduced IGF-1 signalling depended on the stability of the mitochondrial genome, first in a 2025 bioRxiv preprint (PMID 40501628) and then in the peer-reviewed Science Advances version (PMID 41931604). In other words, the study reported that the same genetic reduction in signalling did not produce the same lifespan outcome when mitochondrial genome integrity differed.

Pharmacological modulation of the pathway

Small molecules are also used to probe the axis. A 2025 study in Free Radical Biology & Medicine reported that chrysophanol delayed ageing phenotypes through the insulin/IGF-1 signalling pathway (PMID 40086491), which is a pathway-targeting result rather than an IGF-1 administration result.

Tissue-specific mechanisms

Two verified papers describe IGF-1 in specific tissues. In the central nervous system, a 2026 Physiology review summarised GH and IGF-1 actions in the brain and their relevance to neuropsychiatric disease (PMID 40623083). In skin, researchers reported an androgen receptor/miR-221/IGF-1 pathway involved in the pathogenesis of androgenetic alopecia, positioning IGF-1 as a node downstream of androgen receptor signalling (PMID 37496996).

Limits of the evidence in Module 2

These mechanistic papers describe pathway architecture, not clinical effect size. Several key results come from C. elegans, where the receptor and downstream transcription factors are homologues rather than identical human proteins. None of these studies administered IGF-1 to humans, and none of them establish that modulating the pathway in a person reproduces the model-organism outcome.

Module 3 — Reported Outcomes by Study

The table below summarises the model, endpoint and reported result for each verified study. It is a summary of what researchers reported, not a list of expected outcomes.

Limits of the evidence in Module 3

None of these endpoints was a controlled efficacy outcome of exogenous IGF-1 in healthy humans. Behavioural, dermatological and lifespan endpoints come from different species and different experimental logics, and the ageing studies mostly reduced signalling rather than increasing it — a direction opposite to the assumption that more IGF-1 is better. No verified study reported body-composition, strength or recovery outcomes in trained adults.

Module 4 — IGF-1 Side Effects: What Studies Report

Risk framing in the doping literature

The most direct adverse-event discussion in the verified set is a 2023 sports-endocrinology review, in which researchers described the use of growth hormone, IGF-1, insulin and erythropoietin as doping agents and discussed the health risks and detection challenges associated with that misuse (PMID 36736729). The review treats these hormones as a risk category rather than as performance tools with a defined safety profile.

Chronic excess as a clinical state

Acromegaly is the clinical model of sustained GH/IGF-1 excess, and the treatment literature is built around lowering both markers; a surgical follow-up study reported the correlation between GH and IGF-1 concentrations during treatment and used both as measures of disease control (PMID 27858572). That framing — high IGF-1 as something clinicians work to normalise — is itself a safety-relevant observation.

The longevity trade-off

Ageing research points in the same direction. A review of insulin, IGF-1 and longevity described reduced signalling as the condition associated with extended lifespan in model systems (PMID 22396862), and researchers later reported that this longevity effect was contingent on mitochondrial genome stability (PMID 41931604). Neither paper reported a safety benefit of raising IGF-1 signalling.

Neuropsychiatric context

A 2026 review of GH and IGF-1 actions in the brain summarised associations between this axis and neuropsychiatric disease states (PMID 40623083), meaning the CNS literature describes both signalling roles and disease associations rather than a clean effect profile.

Limits of the evidence in Module 4

The verified set contains no randomised placebo-controlled trial reporting a tabulated adverse-event list for administered IGF-1, no incidence rates, and no dose-toxicity relationship. Commonly discussed concerns such as hypoglycaemia or tissue overgrowth are not quantified in any paper cited here, so no frequency figures are given.

Module 5 — Pharmacokinetics Where Data Exist

The verified literature used for this course does not report pharmacokinetic parameters for exogenous IGF-1: there are no half-life, clearance, bioavailability, C_max or T_max values in these papers. What the set does contain is information about the determinants of endogenous IGF-1 concentration.

• GH dependence. Researchers reported a correlation between GH and IGF-1 during acromegaly treatment, indicating that IGF-1 concentrations move with upstream GH secretion, though not identically in all patients (PMID 27858572).
• Microbiome dependence. A review described the gut microbiota as an influence on circulating IGF-1 and on bone outcomes linked to it (PMID 29362822).
• Receptor-level interference. A 2025 study reported that virally encoded insulin/IGF-like peptides inhibited IGF-1 receptor signalling, illustrating that competitor ligands can alter pathway activity independent of circulating IGF-1 concentration (PMID 40829596).

Limits of the evidence in Module 5

Determinants of endogenous levels are not a substitute for pharmacokinetic data on an administered peptide. Nothing in this set supports statements about how long an injected form persists, how it distributes, or how binding proteins alter exposure in humans.

Module 6 — Regulatory Status, Stated Factually

Approved products

Recombinant human IGF-1 exists as an approved prescription medicine (mecasermin) with a narrow labelled indication in severe primary IGF-1 deficiency, prescribed and monitored by physicians. Approval of a recombinant hormone for a specific deficiency state does not extend to other uses, and none of the verified papers evaluated the approved product outside a clinical context.

Research-use-only material

Peptides and peptide analogues labelled "for research use only" (RUO) are not approved medicines. RUO labelling indicates material intended for laboratory investigation, without the identity, purity, sterility and manufacturing oversight that applies to approved drug products, and without human-use authorisation.

Compounding

In the United States, compounded preparations fall under sections 503A (traditional pharmacy compounding) and 503B (outsourcing facilities) of the Federal Food, Drug, and Cosmetic Act. A bulk drug substance must meet defined eligibility criteria to be compounded, and the FDA maintains lists that determine which substances may be used; several peptide substances have been placed in categories that restrict compounding. Compounded preparations are not FDA-approved products.

Sport and anti-doping

IGF-1 is treated as a doping agent in competitive sport, and a 2023 review discussed growth hormone, IGF-1, insulin and erythropoietin together in that context, including detection difficulties (PMID 36736729).

Limits of the evidence in Module 6

Regulatory frameworks differ by country and change over time, and the verified scientific papers were not written to describe regulation. This section is general information, not legal advice.

What the studies did not test

Across the verified literature, several questions remain untested:

1. Exogenous IGF-1 in healthy adults. No verified study administered IGF-1 to healthy people and measured performance, body composition or recovery.
2. Dose–response. No verified paper reported a human dosing schedule, so none is described on this page.
3. Long-term safety. The ageing literature reported that reduced signalling extended lifespan in models and that this depended on mitochondrial genome stability (PMID 41931604); the reverse experiment — long-term elevation in humans — was not tested.
4. Translation of tissue findings. The androgenetic alopecia pathway work described a mechanism (PMID 37496996) but was not a clinical treatment trial, and the fear-extinction finding (PMID 33792539) was a preclinical behavioural result.
5. Comparative analogue data. No verified paper compared IGF-1 with modified analogues on any endpoint.

Readers evaluating claims about IGF-1 can check whether a given assertion maps onto one of these gaps. This page is for educational purposes only and is not medical advice; consult a licensed physician before making any decision related to hormones, peptides or prescription medicines.

References

• Doping and sports endocrinology: growth hormone, IGF-1, insulin, and erythropoietin (Revista Clinica Espanola, 2023)
• The AR/miR-221/IGF-1 pathway mediates the pathogenesis of androgenetic alopecia (International Journal of Biological Sciences, 2023)
• Growth Hormone and IGF-1 Actions in the Brain and Neuropsychiatric Diseases (Physiology, 2026)
• IGF-1 facilitates extinction of conditioned fear (eLife, 2021)
• Insulin, IGF-1 and longevity (Aging and Disease, 2010)
• Gut Microbiota and IGF-1 (Calcified Tissue International, 2018)
• Viral insulin/IGF-like peptides inhibit IGF-1 receptor signaling to enhance viral replication (Cell Reports, 2025)
• Chrysophanol delays aging via insulin/IGF-1 signaling pathway (Free Radical Biology & Medicine, 2025)
• Reduced insulin/IGF-1 signaling and loss of pals-22 promote repetitive DNA silencing in C. elegans (microPublication Biology, 2025)
• The longevity effects of reduced IGF-1 signaling depend on the stability of the mitochondrial genome (Science Advances, 2026)
• The longevity effects of reduced IGF-1 signaling depend on the stability of the mitochondrial genome (bioRxiv, 2025)
• Correlation between GH and IGF-1 during treatment for acromegaly (Journal of Neurosurgery, 2017)