IGF-1 LR3 (Long R3 IGF-1) is an engineered analog of human insulin-like growth factor 1, built for mammalian cell culture, and it has never been approved as a drug anywhere. It differs from native IGF-1 by one amino-acid swap and a 13-residue extension, changes that make it far less likely to be held by IGF binding proteins. It shouldn't be confused with mecasermin (Increlex), the FDA-approved form of human IGF-1. WADA bans it at all times.
Notice: Research peptides are sold for in-vitro laboratory research only. They are not FDA-approved, not for human or animal consumption, and this page is not medical advice. It contains no dosing or use guidance.
What IGF-1 LR3 is
Insulin-like growth factor 1 (IGF-1) is a 70-amino-acid protein hormone. In blood and in cell culture, most IGF-1 is held by IGF binding proteins (IGFBPs), which limit how much reaches cells.
Long R3 IGF-1 was designed to get around that. Repligen, which sells it under the LONG® R³ IGF-I trademark, describes it as a "recombinant analog of human insulin-like growth factor-I" with two changes:
- The "R3": an arginine substituted for glutamic acid at position 3.
- The "Long": a 13-amino-acid N-terminal extension peptide, which Repligen says is a portion of growth hormone sequence used to improve production.
Repligen reports "> 1000 fold reduced affinity for IGFBPs" compared with native IGF-1. One reagent supplier, ProSpec, lists it as an 83-amino-acid, non-glycosylated chain of about 9.1 kDa, produced in E. coli.
What it's actually used for
Long R3 IGF-1 is a biomanufacturing and lab reagent. Repligen markets it to support cell growth, density and viability and to raise protein yield in CHO cell culture, and lists HEK 293, Vero, MDCK and fibroblast lines among compatible cells.
Reagent suppliers sell it with explicit restrictions. ProSpec's page says its products are "furnished for LABORATORY RESEARCH USE ONLY" and "may not be used as drugs." We found no FDA approval for IGF-1 LR3 in any form.
IGF-1 LR3 vs mecasermin (Increlex)
The approved drug in this family is mecasermin, sold as Increlex. The two are often lumped together online. They're different molecules with different regulatory standing.
| IGF-1 LR3 (Long R3 IGF-1) | Mecasermin (Increlex) | |
|---|---|---|
| Structure | 83 amino acids: Arg3 substitution plus 13-residue extension | 70 amino acids, identical to human IGF-1 |
| Binding proteins | Repligen reports >1,000-fold lower IGFBP affinity | Binds IGFBPs like native IGF-1 |
| Intended use | Cell-culture supplement | Prescription drug |
| FDA status | Not approved | Approved 2005 |
| Source | Repligen | FDA label, July 2025 |
Increlex's FDA label (revised July 2025) describes mecasermin as recombinant human IGF-1 made in E. coli, approved to treat growth failure in children with severe primary IGF-1 deficiency or with growth hormone gene deletion and neutralizing antibodies to GH. The label's warnings show why IGF-1 activity is handled carefully even in an approved product:
- Hypoglycemia: "Severe hypoglycemia leading to hypoglycemic seizures has been observed" with Increlex.
- Malignant neoplasia: the label reports "several cases of malignant neoplasia" in treated children and lists malignancy as a contraindication.
- Other warnings: hypersensitivity and anaphylaxis, intracranial hypertension, lymphoid tissue hypertrophy and slipped capital femoral epiphysis.
None of that clinical data describes IGF-1 LR3. A molecule engineered to escape binding proteins hasn't been through the trials that produced the Increlex label.
Regulatory status (October 2026)
- FDA: IGF-1 LR3 isn't an approved drug. In an April 1, 2020 warning letter to Tailor Made Compounding, FDA listed "IGF1-LR3" among bulk substances the pharmacy used that weren't eligible for compounding. It doesn't appear on FDA's Category 2 compounding page (content current as of April 22, 2026). FDA's position on "research use only" labels is covered in FDA peptide regulation in 2026.
- 2026 warning letters: the two August 24, 2026 letters we checked, to Royal Peptides and Peptide Partners, don't name IGF-1 LR3. That doesn't mean sellers are in the clear; FDA judges intended use from the whole website.
- WADA: the 2026 Prohibited List bans "Insulin-like growth factor 1 (IGF-1, mecasermin) and its analogues" under S2.3, at all times (WADA; 2026 list text). The same section covers mechano growth factors.
- DEA: we found no federal scheduling action for IGF-1 LR3 as of October 21, 2026.
More: are peptides legal? and peptide regulatory news.
Research-grade vials: what the market looks like
As of October 21, 2026, 47 vendors in our IGF-1 LR3 price index had it in stock, at a median of $80.00 per mg. The cheapest listings are 1 mg vials, so per-mg prices look high next to most peptides. The cheapest in-stock listings:
| Vendor | Listing | Price | $/mg | Review |
|---|---|---|---|---|
| Bulk Peptide Supply | IGF-1 LR3 1mg | $30.00 | $30.00 | Review |
| Go Alpha Labs | IGF-1 LR3 1mg | $46.89 | $46.89 | Review |
| Recon Peptides | IGF-1 LR3 1mg | $55.00 | $55.00 | Review |
Prices are as listed on vendors' sites on October 21, 2026 and change often. A low price says nothing about identity or content. Compare sizes with the peptide price comparison tool, and if you need to convert micrograms to milligrams, use the unit converter.
How to check an IGF-1 LR3 COA
IGF-1 LR3 is a recombinant protein, not a short synthetic peptide, so a certificate should look a little different from a typical BPC-157 report.
- Identity by mass. The measured mass should match the roughly 9.1 kDa, 83-residue molecule. A mass near 7.6 kDa would suggest native-sequence IGF-1 instead.
- The compound is named as IGF-1 LR3 (or Long R3 IGF-1), not "IGF-1" alone. The two are different products.
- Measured content vs label. Small vials magnify fill errors. Read peptide purity vs net content.
- Endotoxin. Bacterially expressed proteins can carry endotoxin. See endotoxin testing for peptides.
- A lot number matching the vial and a named lab you can verify. Our COA guide and COA checklist walk through it.
Bottom line
IGF-1 LR3 is a cell-culture reagent with a long, well-documented record in biomanufacturing and no record as an approved medicine. The approved IGF-1 drug, mecasermin, is a different molecule with its own serious label warnings. If you're comparing suppliers for lab work, start with documentation: see how to choose a peptide vendor and third-party tested peptides.
Sources are linked inline and were checked October 21, 2026.
