IGF-1 LR3 is sold to people who want the growth-promoting effects of insulin-like growth factor 1 without a prescription. It was built for laboratories, not patients: a modified IGF-1 that cells in culture can use more efficiently. What the literature says about doses — 44 indexed papers, none in humans — is on our IGF-1 LR3 dosage page. This page takes the harder question: what is known about harm when nobody has ever measured it.
The record, counted
Searched on 30 September 2026:
| Where a finding would be | Query | Result |
|---|---|---|
| ClinicalTrials.gov (v2 API) | "IGF-1 LR3" | 0 studies |
| openFDA adverse-event database | product "IGF-1 LR3" | 0 reports |
| openFDA adverse-event database | product "IGF-1" | 4 reports: three list it as a concomitant product beside growth hormone or other medicines; one, from Australia in 2014, lists "IGF-1" among more than a dozen suspect products — testosterone, nandrolone, growth hormone, clenbuterol and "arsenic compounds" — with liver, kidney and bone-marrow failure. None names LR3, and none can be attributed to IGF-1 |
| PubMed | "IGF-1 LR3" | 44 records; our dosage page read all 44 and found no human study |
A 2026 review of performance-enhancing peptides in Frontiers in Endocrinology, written for clinicians, sorts these compounds into evidence tiers. IGF-1 LR3 sits in the bottom tier with the plain entry "no peer-reviewed human studies", its half-life "not documented", and claims about it resting "on extrapolation rather than direct human data".
Why the molecule matters for side effects
IGF-1 LR3 is human IGF-1 with two changes: arginine replaces glutamic acid at position 3, and a 13-amino-acid extension is added at the front, making 83 amino acids instead of 70. In the body, most IGF-1 travels bound to IGF-binding proteins, which hold it inactive and regulate how much reaches the receptor. The LR3 changes cut that binding sharply. The review summarises the consequence: it engages the same receptor and is presumed to trigger the same growth and metabolic signalling, but "its altered binding characteristics may influence the magnitude or temporal dynamics of pathway activation." In plain terms, one of the body's brakes on IGF-1 is designed out, and nobody has measured what that does in a person.
The nearest labelled record: mecasermin (Increlex)
The only IGF-1 drug with a US label is INCRELEX, whose active ingredient, mecasermin, is recombinant human IGF-1 identical to the body's own. It is approved for children with severe primary IGF-1 deficiency, given by injection twice daily at weight-based doses under specialist supervision. Its label (effective 18 May 2026) is the closest thing to a measured safety record for the receptor IGF-1 LR3 acts on.
From its clinical studies — 71 children, mean 3.9 years of treatment, 274 subject-years:
- Hypoglycaemia: 30 of 71 (42%) at least once. Five had severe episodes needing assistance; four had hypoglycaemic seizures or lost consciousness. Episodes were most frequent in the first month. The label requires each dose within 20 minutes of a meal or snack and warns against driving or exercise for 2 to 3 hours after dosing while tolerance is established.
- Tonsil and adenoid growth: 11 of 71 (15%), leading to 7 operations; three children had obstructive sleep apnoea.
- Raised pressure inside the skull (intracranial hypertension): 3 children, with headache, visual changes, nausea or vomiting as the signs the label lists.
- Other reactions in 5% or more: lipohypertrophy and bruising at injection sites, ear problems including fluid in the middle ear and hearing loss, headache, dizziness, convulsions, vomiting, joint and limb pain, heart murmur, thymus enlargement.
- Organs and blood tests: kidney and spleen length grew rapidly in the first years, some beyond the 95th percentile; mild rises in AST and LDH were common; a few children showed enlarged hearts or valve changes on echocardiography without symptoms, which the label says cannot be attributed without a control group. Thickening of the soft tissues of the face was seen in several patients.
From its warnings:
- Cancer. Malignant neoplasms have been reported after marketing. The label states it is unknown whether mecasermin caused them, that most occurred in children with conditions predisposing to cancer, and that tumours "were observed also more frequently" at higher than recommended doses or with serum IGF-1 above the normal range. Mecasermin is contraindicated in active or past malignancy.
- Allergy: anaphylaxis requiring hospitalisation, estimated at 0.3% after marketing.
- Bones in growing children: slipped capital femoral epiphysis and progression of scoliosis.
From FDA's database: 809 reports name mecasermin (430 coded serious, data updated 30 July 2026). The most frequent terms are off-label use (132), headache (68), hypoglycaemia (62), vomiting (44) and injection-site pain (41).
Why that label is not IGF-1 LR3's record
Every figure above comes from children with a genuine IGF-1 deficiency, receiving a pharmaceutical product of known content and dose, with glucose monitoring and specialist follow-up. Research-market IGF-1 LR3 is a different molecule, used by adults with normal IGF-1, often alongside growth hormone, secretagogues or anabolic steroids, from vials whose content is not verified. The mecasermin record shows which systems IGF-1 signalling touches; it does not tell anyone how often LR3 causes anything.
What was in the one vial that was analysed
In 2010 the Cologne anti-doping laboratory analysed an injection vial sold on the black market as Long-R3-IGF-I. Mass spectrometry confirmed Long-R3-IGF-I — with a six-histidine tag attached by a two-amino-acid linker. Tags like this are added so a protein can be purified in a laboratory, and are normally removed. The authors wrote that the effects of the tagged form in humans "have not been elucidated or described", and that the product looked more like a by-product of biochemical research than something made for injection. It is a single vial, from 2010, and says nothing about any current product; it does show that what is in a vial is an open question. Our guide to reading a certificate of analysis sets out what a certificate can and cannot settle.
What is not established
- Any human side-effect rate for IGF-1 LR3, at any dose.
- Its effect on blood sugar in people, its half-life, or how long its effects last.
- Any long-term effect, including on cancer risk, organ growth or the heart.
- What it does combined with growth hormone, secretagogues or anabolic steroids.
Symptoms of low blood sugar — shaking, sweating, confusion — after an IGF-1-type injection are a reason for urgent care, not a forum question. Anyone using or considering it should take the label comparison above to a doctor. The training-audience claims made for IGF-1 LR3 are covered by MuscleLedger's IGF-1 LR3 profile; what it is and how it acts, by Peptide Lexicon's IGF-1 LR3 entry. The wider pattern across research compounds is on our peptide side-effects overview.
Sources and dates
- ClinicalTrials.gov v2 API, term "IGF-1 LR3": 0 studies, 2026-09-30. openFDA drug adverse-event endpoint: medicinal product "IGF-1 LR3" (no matches); "IGF-1" (4 reports, drug characterisation and reactions read); generic name "mecasermin" (809 total, 430 serious, top reaction terms), dataset updated 2026-07-30.
- INCRELEX (mecasermin) injection, Ipsen Biopharmaceuticals, application 021839: openFDA label effective 2026-05-18, sections 2, 4, 5, 6.1, 6.2 and 11. Read 2026-09-30.
- Dominikowski A et al. The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis. Front Endocrinol 2026;17:1822475 (PMID 42395176; full text PMC13322892, sections on IGF-1 LR3 and evidence tiers read).
- Kohler M et al. Detection of His-tagged Long-R3-IGF-I in a black market product. Growth Horm IGF Res 2010;20(5):386-390 (PMID 20675162).
- PubMed via NCBI E-utilities, "IGF-1 LR3": 44 records, 2026-09-30.
Corrections go to the contact page.