IGF-1 LR3
Also known as Long R3 IGF-1, LR3 IGF-1, Long Arg3 IGF-1, LONG R3 IGF-I, IGF-1 Long R3
IGF-1 LR3 is a long-acting recombinant analog of insulin-like growth factor 1, engineered to evade binding proteins so it activates the IGF-1 receptor for a markedly extended duration.
Typical use cases
Dosing guidelines
Titration
Community protocols commonly describe starting at the low end (e.g., ~20-40 mcg) and adjusting based on tolerance, with cycles often run for limited periods (frequently cited as roughly 4 weeks on) rather than continuously; framed here for informational tracking only, not as guidance.
Reconstitution
Supplied as lyophilized powder; commonly reconstituted with bacteriostatic water added slowly down the vial wall and gently swirled (not shaken). Example commonly cited: 1 mg vial + 3 mL bacteriostatic water yields ~333 mcg/mL.
Injection sites
Subcutaneous injection, typically into subcutaneous fat of the abdomen (around 2-3 inches from the navel) or upper thigh
Storage & handling
Lyophilized powder stored frozen at -20 C (up to ~12 months); after reconstitution, refrigerate at 2-8 C and use within ~30 days; avoid repeated freeze-thaw cycles and protect from light.
Side effects
- Hypoglycemia (low blood sugar from insulin-like activity)
- Injection-site reactions (redness, swelling, soreness)
- Localized tissue/organ growth or swelling at active sites
- Headache and lightheadedness
- Edema / fluid retention
- Stimulation of proliferative/neoplastic tissue growth (theoretical mitogenic risk)
Research summary
IGF-1 LR3 (Long R3 IGF-1) is an 83-amino-acid analog of native human IGF-1 carrying a glutamic-acid-to-arginine substitution at position 3 and a 13-residue N-terminal extension. These modifications sharply reduce its affinity for IGF binding proteins (IGFBPs) while preserving binding to the IGF-1 receptor; because circulating IGF-1 is normally sequestered and cleared by IGFBPs, the analog remains free in circulation and shows a substantially longer functional half-life (reported around 20-30 hours versus roughly 10 minutes for free native IGF-1) and approximately threefold greater in-vitro potency. Mechanistically, IGF-1 receptor activation drives the PI3K/Akt/mTOR and MAPK cascades, increasing muscle protein synthesis, suppressing FoxO-mediated proteolysis, and promoting satellite-cell proliferation and differentiation; these pathways are well characterized in peer-reviewed IGF-1 biology. The strongest evidence base is preclinical and cell-based: animal and in-vitro studies of IGF-1 (and Long R3 as a research reagent used to optimize cell-culture growth) document hypertrophy, anti-atrophy, and tissue-repair effects, and IGF-1 overexpression models prevent age-related and injury-related muscle loss. However, controlled human clinical trials of IGF-1 LR3 specifically for muscle growth or performance are essentially absent; most human-use information derives from non-peer-reviewed athletic and bodybuilding community reports rather than registered trials. Key limitations include the lack of long-term human safety data, theoretical concerns about systemic mitogenic and proliferative signaling (including effects on existing neoplasia), and hypoglycemia risk from insulin-like activity. It is not an approved therapeutic drug for human use and is widely sold as a research-only reagent.
Key references
- https://en.wikipedia.org/wiki/IGF-1_LR3
- https://pmc.ncbi.nlm.nih.gov/articles/PMC4665094/
- https://pmc.ncbi.nlm.nih.gov/articles/PMC7564605/
- https://pubmed.ncbi.nlm.nih.gov/26615583/
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Educational reference only — not medical advice. Dosing figures are commonly-cited ranges, not prescriptions. Consult a qualified clinician.
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