IGF-1 LR3

What is IGF-1 LR3?

IGF-1 LR3—also written Long R3 IGF-I, Long [Arg3] IGF-I, or LR3IGF-I—is an engineered analogue of human IGF-1. Native IGF-1 has 70 amino acids; LR3 has 83: a 13-aa N-terminal extension plus Arg substitution at position 3 (~9.1 kDa).

Modifications substantially reduce binding to several IGFBPs while retaining IGF-1 receptor activity. Three corrections: (1) LR3 is not native IGF-1 / mecasermin; (2) reduced IGFBP binding ≠ slow clearance; (3) “Long” is structural, not an established 20–30 hour human half-life.

Regulatory status

IGF-1 LR3 is not an FDA-approved drug and has no approved indication, label, dosage, or human prescribing information. A UNII / GSRS substance record is an identity entry—not product approval. Commercial Long R3 material is typically supplied for cell-culture or research use and is not approved for human applications. “Research use only” is a sales restriction, not a clinical quality standard.

No human clinical dosage has been established

A search for the exact analogue and common name variants did not identify a prospective human trial in which participants received IGF-1 LR3. Simple body-weight scaling is not a valid way to turn animal exposures into a self-administration protocol.

There is currently no FDA-approved dosage for IGF-1 LR3. No human dose calculator is provided because no human dose exists to calculate.

IGF-1 LR3 is not mecasermin

Mecasermin (Increlex) is recombinant human IGF-1 approved for narrow pediatric growth-failure indications. The mecasermin label is a biological warning signal (severe hypoglycemia/seizures, hypersensitivity, intracranial hypertension, tissue hypertrophy, neoplasia warnings)—but it cannot set LR3 event rates or doses. Even mecasermin’s ~5.8-hour labeled SC half-life in a small pediatric PK sample does not establish LR3’s half-life.

How IGF-1 LR3 works

1. IGF-1 receptor activation. Downstream PI3K–Akt–mTOR and Ras–MAPK/ERK pathways can affect glucose handling, protein synthesis, survival, proliferation, and tissue growth.
2. Reduced IGFBP affinity. In rat-focused comparisons, native IGF-1 had ~1,000-fold greater affinity than LR3 for several IGFBPs; LR3 was more potent in several endpoints—but potency is endpoint-, species-, and schedule-dependent.
3. Insulin-like metabolic activity. Acute pig/marmoset research found low-IGFBP-affinity analogues had more potent or prolonged hypoglycemic action than native IGF-1—making hypoglycemia a foreseeable hazard.

Half-life: why the 20–30 hour claim is unreliable

Many online pages state a 20–30 hour half-life. No dedicated human PK study supporting that number was identified. Primary rat research reports LR3 is removed from plasma much more rapidly than native IGF-1 because of poor IGFBP association—yet it can remain biologically potent because free receptor availability changes.

Preclinical dosage used in published research

These are animal experiments, not human dosing recommendations. Continuous infusion, intermittent injection, and acute boluses answer different questions. Effects were not restricted to skeletal muscle—gut, kidney, spleen, adrenal, endocrine feedback, and glucose regulation were affected in some models.

IGF-1 LR3 research dosage: commonly reported protocols

The commonly reported online range is approximately 20–100 mcg/day, usually once daily SC or IM, often for 4–6 weeks. The original source of the convention could not be verified. Vial sizes, bodybuilding tradition, and vendor-page copying are more plausible explanations than clinical optimization.

Evidence does not establish that 20–100 mcg is safe or effective, that post-workout timing helps, that IM creates localized growth, that 4–6 weeks is optimal, that human half-life is 20–30 hours, or that stacks with GH/insulin/secretagogues are safe.

Insulin combination warning: Stacking LR3 with insulin or other glucose-lowering agents can make hypoglycemia less predictable and can produce seizure, loss of consciousness, injury, or death. No controlled human study establishes a safe combination protocol.

Research protocol variations

1. SC vs IM. Animal literature includes SC infusion/injection. Online reports describe both SC and IM. No human study compares absorption, safety, or outcomes. IM is not proven “more targeted.”
2. Post-workout timing. Extrapolation from exercise physiology—not a controlled LR3 timing trial.
3. Once-daily vs split. Often justified by the unsupported long half-life claim. Animal infusion vs injection shows schedule matters—not a human split protocol.
4. 4–6 week cycles. No human study established cycle length or required time off.
5. “Site-specific” protocols. Not supported by controlled human evidence.
6. Combinations. Insulin stacks are especially hazardous. GH/secretagogue stacks are unevaluated with LR3 in humans.

Why these reported doses appear online

1. Repetition rather than dose finding — secondary commercial/community material.
2. Confusion with mecasermin — mg/kg BID pediatric label cannot convert to LR3 mcg.
3. Confusion about “Long” — structural name misread as long-acting PK.
4. Convenience and vial size — packaging arithmetic ≠ pharmacology.

Dosage evidence ladder

IGF-1 LR3 dosing is not established for human use. Preclinical literature shows biological activity and potential hazard, but not a therapeutic window in people. Online precision (“start at 20 mcg,” “never exceed 100 mcg”) should not be mistaken for evidence.

Dose escalation

No formal human dose-escalation, MTD, or dose-ranging study was identified. Anecdotal “beginner 20 → advanced 80–100 mcg” sequences have no controlled validation. Because hypoglycemia and broad growth signaling may lack reliable subjective warning, “increase until side effects” is not an evidence-based safety strategy.

Safety and tolerability

No controlled human LR3 safety cohort was identified—so claims like “usually mild” or “safe below 100 mcg” lack an adequate denominator. Hypoglycemia is the most immediate concern. Animal experiments report multi-organ weight changes. Mecasermin labeling supplies IGF-axis warning signals (including neoplasia contraindications/warnings) that are relevant caution—not LR3 incidence rates.

Sporting status

WADA prohibits IGF-1 and its analogues at all times. Anti-doping laboratories have developed methods to detect Long R3 IGF-I. A “research” label does not make use permissible for tested athletes.

Sourcing and origin checks

• Exact LR3 vs native IGF-1 vs mecasermin vs DES?
• Human, animal, or in vitro—and which route?
• Is “half-life” measured peptide, detection window, or vendor claim?
• Does a “human protocol” cite a human LR3 trial—or only general IGF-1 biology?
• Is mecasermin dosing being silently relabeled as LR3 guidance?

Bottom line

IGF-1 LR3 has no FDA-approved dosage and no dedicated human dose-ranging or PK study identified. The familiar 20–100 mcg daily range, post-workout timing, local IM claims, 4–6 week cycles, and 20–30 hour half-life are online conventions rather than clinical conclusions.

Make the absence of a human LR3 protocol—not the apparent precision of anecdotal numbers—the central finding. Mecasermin warns about IGF-1 biology but is a different molecule.

Frequently asked questions

Primary references

• Ballard FJ et al.

  Effects of interactions between IGFBPs and IGFs on plasma clearance and biological activity

  Growth Regulation, 1993.

• Tomas FM et al.

  Potency of infused IGF-I analogues after injection or continuous infusion in rats

  Journal of Endocrinology, 1996.

• Tomas FM et al.

  Acute hypoglycemic potency of IGF-I analogues that bind IGFBPs poorly

  Journal of Endocrinology, 1997.

• Conlon MA et al.

  Long R3 IGF-I infusion, organ growth, and circulating IGF/IGFBP changes in guinea pigs

  1995.

• Dunaiski V et al.

  Growth and endocrine responses to Long R3 IGF-I in finishing pigs

  1997.

• FDA DailyMed

  Increlex (mecasermin) prescribing information

  Approved rhIGF-1 — not LR3 dosing.

• WADA

  Statement on IGF-1 as a prohibited substance

  IGF-1 and analogues prohibited at all times.