Conservative
Community- Dose
- 20–30 mcg
- How often
- Once daily with food
- How long
- 4 weeks, then 4+ off
Common start to gauge blood-sugar response.
Draw 6–9 units1 mg + 3 mL
PreclinicalIGF-1 analog
IGF-1 LR3
Long R3 IGF-I
- Common dose
- 20–50 mcg daily
- Cycle
- 4 weeks on, 4 off
- Vial sizes
- 0.1, 1 mg
- Typical draw
- 6 units1 mg with 3 mL, 20 mcg
An engineered 83-amino-acid form of IGF-1 that barely binds IGF-binding proteins, so more of it stays free to act: in animal studies it was several times as potent as natural IGF-1, though it left the blood faster.
Evidence. No human trials; developed as a cell-culture supplement. The approved IGF-1 drug (mecasermin) is a different molecule.
Status
- Approval
- Not approved as a drug in the US or EU. It is sold as a cell-culture reagent; the approved IGF-1 drug, mecasermin (Increlex), is a different molecule.
- Sport (WADA 2026)
- Banned in sportS2.3 growth factors: insulin-like growth factor 1 (IGF-1, mecasermin) and its analogues. Banned at all times.
Sport status follows the WADA Prohibited List in force since January 1, 2026; athletes should confirm with their anti-doping organization. Checked October 5, 2026. Status of every compound.
How it works
IGF-1 LR3 is a lab-made form of IGF-1, the growth factor the liver makes in response to growth hormone, with 13 extra amino acids at the start and an arginine swap at position 3. These changes mean IGF binding proteins, which normally hold IGF-1 inactive, barely grab it, so more reaches the IGF-1 receptor, which drives cell growth and lowers blood sugar. In rats and pigs it was 2–6 times as potent as IGF-1, though it left the blood faster.
AnimalMainly from cell and animal studies; not shown in people.
Not known
It has never been tested in people, so how long it lasts after an injection, how far it lowers blood sugar and whether it affects cancer risk are unknown.
Protocol
Community
20–100 mcg once daily; 20–50 mcg is most often cited.
- Frequency
- Once daily
- Route
- Subcutaneous injection (community)
- Timing
- With food or after training. Avoid bedtime because of the low blood sugar risk.
- Cycle
- About 4 weeks on, at least 4 weeks off.
4 weeks on, 4 off, shown over 26 weeks
Common protocols
The ways IGF-1 LR3 is most often run, each tagged with where it comes from.
Standard
Community- Dose
- 40–50 mcg
- How often
- Once daily, post-workout or morning with food
- How long
- 4 weeks, then 4+ off
Most cited range. Guides say returns diminish above about 50–60 mcg while side effects rise.
Draw 12–15 units1 mg + 3 mL
Post-workout into muscle
Community- Dose
- Same daily total, split left and right
- How often
- After training
- How long
- 4–6 weeks
Injected into the muscles just trained. A local effect is claimed but unproven; it spreads through the body.
Taking it
Where it goes
Subcutaneous (belly or upper thigh) is most common. Some inject into the muscle trained that day, split left and right; it still acts body-wide.
If you miss a dose
No published guidance; skip it and don’t double up. For context, the approved IGF-1 drug (mecasermin) is skipped when a meal is skipped and never made up.
What to expect
- First weeks
Low-blood-sugar risk is highest early, especially if dosed without food.
Community - Weeks 4–6
Guides agree effects plateau, which is why cycles are kept short.
Community - Any time
No human data on muscle or fat effects exist; reported gains are anecdotal.
Community
Side effects and what to do
Low blood sugar: shaky, sweaty, hungry, confused (mecasermin, a different drug: 42% in trials)
Dose with food and keep fast carbs on hand. Fainting or a seizure is an emergency.
Water retention
Usually dose-related and reversible. Lower the dose.
Joint discomfort
Usually mild. Lower the dose or stop.
Stop and get medical help
Confusion, fainting or seizure (low blood sugar), headache with vision changes, belly swelling that keeps growing, or a new or growing skin lesion: stop and get medical help.
Who should avoid it
No product label covers IGF-1 LR3, so these come from human studies and from precautions based on how it works. Most important first.
- Diabetes, insulin use or low blood sugar
- PrecautionIGF-1 lowers blood sugar like insulin. In pigs, LR3 lowered it 2–3 times as strongly as IGF-1, and for longer; the mecasermin label warns of severe lows causing seizures (by analogy).
- Anyone with active or past cancer
- PrecautionIt acts on the IGF-1 receptor, which drives cell growth. The mecasermin label rules out its use in children with cancer or a history of it (by analogy).
- Children and teens
- PrecautionThe mecasermin label warns of slipping of the hip’s growth plate and worsening scoliosis in growing children (by analogy). This compound has never been tested in children.
- Pregnancy or breastfeeding
- PrecautionNo human safety data exist.
- Anyone relying on product quality
- PrecautionIt is made and sold as a cell-culture reagent, not a drug, so vials have no regulated standard for injection: identity, purity, sterility or amount.
Interactions
No interaction studies have been published, and no product label lists any.
Precaution: follows from how it works or from a related drug, and hasn’t been tested. This isn’t a complete list: a pharmacist or doctor can check a specific medicine or condition.
Tracking and pairing
Worth tracking
- Blood glucose, especially in the first week
- Low-blood-sugar symptoms
- Waist size (unexplained belly growth)
Often paired with
Usually run on its own.
Human studies
No published human studies of IGF-1 LR3 turned up in our October 2026 review. The evidence note at the top of this page sums up what is known.
Limits of the evidence
No human study has tested IGF-1 LR3. What is known comes from rat, pig and cell studies from the 1990s, and the effects differed by species: it boosted growth in rats but slowed it in pigs. The approved IGF-1 drug, mecasermin, is a different molecule given to children with severe IGF-1 deficiency. The doses people inject, effects on blood sugar, long-term cancer risk and product purity are untested.
Mixing your vial
| Vial | Water | Common dose | Draw | Strength | Action |
|---|---|---|---|---|---|
| 0.1 mg | 1 mL | 20 mcg | 20 units (0.20 mL) | 0.1 mg/mL | |
| 1 mg | 3 mL | 20 mcg | 6 units (0.06 mL) | 0.3333 mg/mL |
The maker of Long R3 IGF-I recommends dissolving it in about 0.6% (100 mM) acetic acid so it doesn’t stick to surfaces. Community guides split between acetic acid and bacteriostatic water. Acidic solutions sting.
Dose chart
Syringe units for common doses at different water volumes. Select a cell to open it in the calculator.
| Dose | Water added | ||
|---|---|---|---|
| 1 mL | 2 mL | 3 mL | |
| 20 mcg | |||
| 25 mcg | |||
| 30 mcg | |||
| 50 mcg | |||
| 60 mcg | |||
| 75 mcg | |||
| 100 mcg | |||
U-100 insulin syringe: 100 units is 1 mL. Draws over 100 units show in mL. Faded values are under 2 units, which is hard to measure. Check that your vial holds the larger volumes.
Datasheet
- Half-life
- No reliable value has been published.
- Type
- Protein, 83 amino acids
- Molecular weight
- about 9,111 g/mol (mass spectrometry)
- Storage before use
- Fridge (2–8 °C) or freezer. Repligen rates its freeze-dried Long R3 IGF-I stable for 5 years at 2–8 °C.
- After mixing or opening
- Suppliers dissolve it in 100 mM acetic acid and keep it at 2–8 °C (R&D Systems: 1 month; Repligen: up to 12 months). With bacteriostatic water, common practice is fridge, about 4 weeks.
- Molecule: R&D Systems datasheet 8335D-GMP (recombinant human LR3 IGF-I): 13-residue extension plus IGF-1 with Arg at position 3
- Storage: Community Repligen LONG R3 IGF-I FAQ; R&D Systems 8335D-GMP datasheet
Every compound side by side: the half-life chart and the storage chart.
Cautions
- Low blood sugar is the main acute risk of IGF-1 drugs.
- Promotes cell growth: avoid with any cancer or cancer history.
- No human safety data.
Questions
What is IGF-1 LR3?
An engineered 83-amino-acid form of IGF-1 that barely binds IGF-binding proteins, so more of it stays free to act: in animal studies it was several times as potent as natural IGF-1, though it left the blood faster.
How does IGF-1 LR3 work?
IGF-1 LR3 is a lab-made form of IGF-1, the growth factor the liver makes in response to growth hormone, with 13 extra amino acids at the start and an arginine swap at position 3. These changes mean IGF binding proteins, which normally hold IGF-1 inactive, barely grab it, so more reaches the IGF-1 receptor, which drives cell growth and lowers blood sugar. In rats and pigs it was 2–6 times as potent as IGF-1, though it left the blood faster. It has never been tested in people, so how long it lasts after an injection, how far it lowers blood sugar and whether it affects cancer risk are unknown.
Is IGF-1 LR3 FDA-approved?
Not approved as a drug in the US or EU. It is sold as a cell-culture reagent; the approved IGF-1 drug, mecasermin (Increlex), is a different molecule.
What is the usual IGF-1 LR3 dose?
From community reports, not established: 20–100 mcg once daily; 20–50 mcg is most often cited. These are the amounts sources reference, not recommendations.
How much water do I mix IGF-1 LR3 with?
There’s no single right amount, because the liquid only sets the strength. With 3 mL of diluent (its maker uses dilute acetic acid) in a 1 mg vial, the strength is 0.3333 mg/mL, so 20 mcg is 6 units on a U-100 insulin syringe. More liquid makes small doses easier to measure. The dose chart above shows other volumes.
Who should avoid IGF-1 LR3?
No product label covers IGF-1 LR3, so these come from human studies and from precautions based on how it works. Diabetes, insulin use or low blood sugar: IGF-1 lowers blood sugar like insulin. In pigs, LR3 lowered it 2–3 times as strongly as IGF-1, and for longer; the mecasermin label warns of severe lows causing seizures (by analogy). Anyone with active or past cancer: It acts on the IGF-1 receptor, which drives cell growth. The mecasermin label rules out its use in children with cancer or a history of it (by analogy). Children and teens: The mecasermin label warns of slipping of the hip’s growth plate and worsening scoliosis in growing children (by analogy). This compound has never been tested in children. The “Who should avoid it” section lists 2 more groups.
How should IGF-1 LR3 be stored?
Before mixing: Fridge (2–8 °C) or freezer. Repligen rates its freeze-dried Long R3 IGF-I stable for 5 years at 2–8 °C. After mixing: Suppliers dissolve it in 100 mM acetic acid and keep it at 2–8 °C (R&D Systems: 1 month; Repligen: up to 12 months). With bacteriostatic water, common practice is fridge, about 4 weeks. This is common practice; no product label covers it.
Is IGF-1 LR3 banned in sport?
Yes. S2.3 growth factors: insulin-like growth factor 1 (IGF-1, mecasermin) and its analogues. Banned at all times.
Has IGF-1 LR3 been studied in people?
No published human studies turned up in our October 2026 review. The evidence note at the top of this page sums up what is known.
Sources
- Increlex (mecasermin) prescribing information, sections 4 and 5, cited by analogy (DailyMed, rev. 05/2026)
For how it works, who should avoid it and the limits of the evidence
- Francis et al., Long R3 IGF-I escapes IGF binding proteins in cell studies (J Mol Endocrinol 1992) PMID 1378742
- Tomas et al., LR3 IGF-I more potent than IGF-I in growing rats (J Endocrinol 1993) PMID 8371075
- Bastian et al., faster plasma clearance of LR3 IGF-I than IGF-I in rats (J Endocrinol 1993) PMID 7693845
- Tomas et al., low-binding IGF-I variants and blood sugar in pigs and marmosets (J Endocrinol 1997) PMID 9415072
- Dunaiski et al., LR3 IGF-I reduced growth in pigs (J Endocrinol 1997) PMID 9488001
Doses tagged Community come from public dosing guides and user reports, checked against at least two of them. Those sites aren’t named here because many of them sell peptides or earn commissions on them.