Some compounds in this market have thin evidence. This one has a literature that is not about humans at all — and reading what it is about explains where the molecule came from.
This is research journalism. It reports what the sources state, including the amounts used in trials and on labels where those are on the record, each figure carrying its source and date — and it never tells anyone what to take.
The registry is empty, and the papers are farm animals
An intervention search of ClinicalTrials.gov for IGF-1 LR3 returns zero results. So does Long R3 IGF-1. There is no registered human study of this molecule.
The published literature is about twenty records. A PubMed search across all fields for "Long R3 IGF-1" OR "LR3 IGF-1" OR "LongR3 IGF-1" returns 21; a narrower title-and-abstract search of the same variants returns five, which is the figure quoted on our evidence ledger. Neither count contains a human study. Here is what the wider set is:
| Subject of the paper | Records |
|---|---|
| Fetal sheep — infusions, islet function, organ growth, cardiomyocytes | 5 |
| Cattle — beef heifer protein metabolism, bovine oocytes, bovine satellite cells | 3 |
| Other animal or tissue work — sheep rumen epithelium, chicken granulosa cells, mouse atherosclerosis, mouse tumour conjugate, murine macrophage precursors | 5 |
| Cell culture and manufacturing — stem-cell differentiation media, recombinant expression in Pichia pastoris | 2 |
| Mouse Alzheimer's model, intranasal | 1 |
| Reviews and commentary | 1 |
The single record closest to the question a lifter is asking was published in 1999 and is titled "Action of long(R3)-insulin-like growth factor-1 on protein metabolism in beef heifers."
What the molecule was built for
The naming is descriptive. Native IGF-1 is 70 amino acids; the LR3 variant substitutes an arginine at position 3 and adds a 13-residue N-terminal extension. Both changes weaken its capture by IGF-binding proteins, which in the body hold the overwhelming majority of circulating IGF-1 inactive. Less capture means a longer-acting, more available growth factor.
That property has an industrial use, and one of the papers states it in its title: "Replacement of insulin by LongR3-IGF-1 allows for the differentiation of ES cells into neuroprogenitors and insulin-secreting cells" (Analytical Biochemistry, 2005). Cell-culture media need a stable growth-factor supplement, insulin degrades and is inefficient at the concentrations required, and a binding-protein-resistant IGF-1 does the job better.
So the compound's real career is as a laboratory reagent for growing cells, and secondarily as a tool for fetal-physiology and livestock research. It reached the injectable market because it was already being manufactured, not because a development programme pointed at people.
The version that does have a human record
There is an approved recombinant human IGF-1, and the comparison is instructive: mecasermin, sold as Increlex under BLA 021839. Its sequence is identical to endogenous human IGF-1 — no arginine substitution, no extension.
Its indication is narrow and paediatric: growth failure in children aged two and over with severe primary IGF-1 deficiency, or with a growth hormone gene deletion who have developed neutralising antibodies to growth hormone. Severe primary IGF-1 deficiency is defined on the label by height and IGF-1 standard-deviation scores of −3.0 or below with normal or elevated growth hormone. The label adds that the product is not a substitute for growth hormone in approved growth-hormone indications, and is not for secondary IGF-1 deficiency from growth-hormone deficiency, malnutrition, hypothyroidism or corticosteroid treatment.
Its warnings section is the only human safety record this molecular family has:
- Severe hypoglycaemia leading to hypoglycaemic seizures — the label's first warning, because IGF-1 has insulin-like effects
- Anaphylaxis requiring hospitalisation
- Intracranial hypertension, with funduscopic examination recommended at initiation and periodically
- Lymphoid tissue hypertrophy — tonsillar and adenoidal
- Slipped capital femoral epiphysis, and progression of scoliosis
- Malignant neoplasia — several cases observed in treated children, with instructions to discontinue
Mecasermin has 40 ClinicalTrials.gov registrations. The LR3 variant has zero.
That is the asymmetry worth carrying away. The version of this hormone that has been through human trials is the unmodified one, given to children who cannot make it, under a label with seven warnings including hypoglycaemic seizures and neoplasia. The version sold for muscle is the one modified specifically to evade the body's mechanism for keeping the hormone in check — and it has never been registered for a human study of anything.
Where it fits on this site's ledger
IGF-1 LR3 is routinely named in automated summaries of muscle-growth peptides, which is how it stays visible despite having no trial record. On the evidence hierarchy this site applies, it sits below every compound on the growth-hormone secretagogue page, because those at least have registrations to count — ipamorelin has three, CJC-1295 has one terminated, and the approved releasing-factor analogue has 24 with a pooled body-composition estimate.
The broader ranking is on the evidence ledger, and the honest comparison with what does have human trials is on our creatine page. For a tested athlete, IGF-1 and its analogues are prohibited at all times — drug testing has the class detail.