IGF-1 LR3 Dosage: The Reagent, Not the Drug
IGF-1 LR3 isn't a drug candidate that stalled somewhere in development, it's a laboratory reagent that was never meant to enter one. Researchers engineered it in 1992 specifically to change how an IGF-1 analog interacts with IGF-binding proteins in cell culture, and that exact property is why biotech suppliers sell it today as a serum-free growth-factor supplement for producing recombinant proteins in bioreactors, not as a therapeutic. No human clinical trial of IGF-1 LR3 itself has ever been conducted. Every dosage number circulating online comes from bodybuilding vendors and forums, not from a single study of this molecule in a person.
Reviewed by the PepGuard team · Last reviewed Jul 28, 2026
Synthetic analog of human IGF-1 carrying a 13-amino-acid N-terminal extension plus a Glu3→Arg3 substitution · also sold as Long R3 IGF-1, Long-Arg3-IGF-I, LR3-IGF-1
Photo: Madeline Liu / UnsplashTwo different drugs, two different unit systems.
The mg/kg rows below are a real FDA-approved drug’s label. The mcg/day rows are vendor convention for a molecule with no human trial behind it.
| What's cited | Range |
|---|---|
| INCRELEX (mecasermin) FDA-approved starting dose — a different, unmodified rhIGF-1 drug, not LR3 | 0.04-0.08 mg/kg, subcutaneous, twice daily |
| INCRELEX (mecasermin) maximum titrated dose (after gradual increases if tolerated) | 0.12 mg/kg, subcutaneous, twice daily |
| Commonly cited IGF-1 LR3 beginner range (vendor-reported, no human trial exists) | 20-30 mcg/day, subcutaneous |
| Commonly cited IGF-1 LR3 split-dose range (vendor-reported, no human trial exists) | 40-50 mcg/day, split into two doses |
| Commonly cited IGF-1 LR3 cycle length (vendor-reported) | 4-6 weeks |
There are two entirely separate numbers systems here, and they shouldn't be read as versions of each other. INCRELEX (mecasermin), the actual FDA-approved IGF-1 drug, is dosed in mg/kg based on body weight, twice daily, with a defined titration schedule from a real drug label. It is indicated only for severe primary IGF-1 deficiency or GH gene deletion with neutralizing antibodies to GH, in patients 2 years and older, not for general use. The mcg/day figures below for "IGF-1 LR3" are a completely different, much smaller unit of measurement, and they come entirely from vendor and bodybuilding-forum convention, not from any completed human trial of IGF-1 LR3 itself.
It was built for bioreactors, not bodies.
In 1992, researchers built a set of fusion-protein analogues of IGF-1 to study how binding-protein interactions affect biological potency. One of them, carrying a 13-amino-acid N-terminal extension and a Glu3→Arg3 substitution, is the molecule sold today as “IGF-1 LR3.” The paper that created it was about cell biology, not therapeutics, and no human trial of any kind has followed it since.
That original finding turned out to have a real industrial use: a 2006 study showed LONG R3IGF-I supporting the growth and survival of cultured cells at concentrations far lower than insulin requires, which is exactly why biotech suppliers sell it today as a serum-free growth-factor additive for producing recombinant proteins in bioreactors, not as an injectable for humans. Checked directly against the FDA’s current 503A bulk drug substances nominated list, IGF-1 LR3 doesn’t appear anywhere on it, unlike BPC-157, TB-500, MOTS-c, Semax, and Epitalon, all of which are actively under FDA Pharmacy Compounding Advisory Committee review this year. It was never nominated, because it was never proposed as a drug candidate in the first place.
Borrowed from a related drug, not from IGF-1 LR3 itself.
These come from INCRELEX’s FDA label, a chemically distinct IGF-1 product. They’re included because IGF-1 LR3 activates the same receptors, not because IGF-1 LR3 has its own trial data.
| Signal | Frequency | Context |
|---|---|---|
| Hypoglycemia, including hypoglycemic seizures | commonly reported | Documented in 42% of subjects in INCRELEX's clinical trials, with severe episodes and seizures in a handful of cases; the FDA label recommends dosing near meals. IGF-1 LR3 activates the same IGF-1 and insulin receptors as native IGF-1, so the mechanism is directly relevant even though LR3 itself has never been tested in a human trial. |
| Lipohypertrophy and injection site reactions | commonly reported | Documented in the INCRELEX label; rotating injection sites is the standard mitigation. |
| Tonsillar or adenoidal hypertrophy (snoring, sleep apnea, middle-ear effusion) | occasionally reported | Reported in about 15% of INCRELEX subjects, concentrated early in therapy; some cases required surgical intervention. |
| Intracranial hypertension (papilledema, headache, vision changes, nausea) | rarely reported | Reported in 3 subjects across INCRELEX's clinical trials; symptoms resolved after dose interruption. |
| Immunogenicity or impurity-related reactions from unregulated research-grade material | unknown / not studied | IGF-1 LR3 sold for human use is unregulated research-chemical material, not pharmaceutical-grade product, and no human safety study of it exists to characterize this risk. |
Not FDA-approved as a drug, and not even part of the FDA's active compounding review process.
IGF-1 LR3 has never been approved by the FDA for any use. Checked directly against the FDA's current "Bulk Drug Substances Nominated for Use in Compounding Under Section 503A" list (updated May 14, 2026), IGF-1 LR3 doesn't appear anywhere in Category 1, 2, or 3. That's a meaningful absence: BPC-157, TB-500, MOTS-c, Semax, and Epitalon are all peptides actively working through that same nomination process, with the FDA's Pharmacy Compounding Advisory Committee reviewing several of them on July 23-24, 2026. IGF-1 LR3 was never even nominated, because it was never proposed as a drug in the first place, it entered circulation as a cell-culture reagent sold by biotech suppliers, not through any pathway meant for human therapeutics. General federal law still applies regardless: under the FD&C Act, any product containing it that's marketed for human use is an unapproved new drug, the same standard the FDA applies to every other unapproved peptide, but no IGF-1-LR3-specific FDA warning letter naming it by name was found on record, so none is cited here. The one real, FDA-approved IGF-1 drug that exists, INCRELEX (mecasermin), is a chemically distinct, unmodified recombinant human IGF-1, approved in 2005 for a specific rare pediatric condition, not the modified analog sold as "IGF-1 LR3."
Every claim above, traced back.
The original 1992 engineering paper, the 2006 cell-culture study, a real FDA drug label, and the FDA’s current compounding nomination list. Click through and check them yourself.
IGF-1 LR3 questions, answered.
There isn't one. No completed human trial of IGF-1 LR3 has ever been conducted, so there's no clinically validated dose to cite. The mcg/day ranges that circulate online come from bodybuilding vendors and forum convention, not from a study of this molecule in a person. The only IGF-1 drug with a real, FDA-approved human dose is INCRELEX (mecasermin), and it's a different, unmodified molecule dosed in mg/kg, not the modified analog sold as IGF-1 LR3.
No. INCRELEX is unmodified recombinant human IGF-1, FDA-approved in 2005 for a specific rare pediatric condition (severe primary IGF-1 deficiency or GH gene deletion with neutralizing antibodies to GH). IGF-1 LR3 is a lab-engineered analog with a 13-amino-acid N-terminal extension and a Glu3→Arg3 substitution, originally created in 1992 to alter how it interacts with IGF-binding proteins in cell culture. They share a name and a receptor, not a regulatory history, a trial record, or a dose.
It's not FDA-approved as a drug. Checked directly against the FDA's current 503A bulk drug substances nominated list (updated May 14, 2026), IGF-1 LR3 doesn't appear in Category 1, 2, or 3 at all, unlike most other research peptides on this site, because it was never nominated as a compounding substance in the first place. Under the FD&C Act, any product containing it that's marketed for human use is still an unapproved new drug, the same general standard applied to every unapproved peptide, even without a warning letter naming it specifically.
It converts a vial's total peptide content, the water volume used to reconstitute it, and a target mcg dose into a draw volume on a syringe. That's real arithmetic, but it's arithmetic applied to a number (the target dose) that was never established by a human study, so the calculator can tell you how to measure a vendor-reported dose accurately, not whether that dose is safe or effective.
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