IGF-1 LR3

Also called Long R3 IGF-I, LR3-IGF-I, long-(Arg3) insulin-like growth factor-I¹

IGF-1 LR3 is a lab-made, longer-acting version of IGF-1, the hormone that carries out much of growth hormone's effect. It has one amino acid swapped and 13 extra added, so the proteins that normally hold IGF-1 in check barely grip it. In rats that made it about 2.5 times as potent as IGF-1.² It was made for laboratory research, and we found no study of it in people.⁴ The only approved IGF-1 drug is mecasermin (Increlex), which is plain human IGF-1, for children with a rare growth disorder. Its label warns about low blood sugar, which affected 42% of children in its trials.⁵ IGF-1 LR3 is sold online for muscle and fat loss without any of that testing.

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At a glance

Where to get it

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Molecular structure

A protein of 83 amino acids: 13 added at the start, then human IGF-1 with one swap. Three disulfide bridges fold it. Too large to draw atom by atom, so this is a sequence diagram.

The added 13-amino-acid extension and the arginine swap

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Length

83 amino acids

Extension

MFPAMPLSSLFVN

Swap

Glu3 → Arg (the "R3")

Bridges

3 disulfide bonds

Formula

C400H619N111O115S9

Weight

9,111.6 Da

CAS

143045-27-6

FDA UNII

M9L22Y19H9

FDA's substance record describes the extension as a modified version of the first 13 amino acids of pig growth hormone.¹ Formula and weight are our calculation from the sequence with IGF-1's three disulfide bonds; FDA's record lists none. The same method gives 7,649 Da for mecasermin, matching its label.⁵

What it is

Growth hormone works largely through IGF-1, made mostly in the liver. In the blood, almost all IGF-1 is held by binding proteins, which limit how much reaches tissues. Australian researchers built variants that dodge those proteins. Long R3 IGF-I was one of them.²

It changes IGF-1 in two ways. Arginine replaces glutamic acid at position 3, and a 13-amino-acid extension is added to the front.^{1, 2} Its main use has been in research. A doping lab that analyzed a black-market vial noted that the tagged form it found is "usually produced for biochemical studies."⁴

The only approved IGF-1 medicine in the US is mecasermin, sold as Increlex. It is identical to human IGF-1 and was approved in 2005, when Ipsen held it; the current label names Eton Pharmaceuticals as manufacturer.^{5, 6} Its label limits it to children 2 and older with severe primary IGF-1 deficiency or growth hormone gene deletion with neutralizing antibodies, and says it "is not a substitute" for growth hormone.⁵

How it works

What's known comes from rat and lab studies.^{2, 3}

• Escapes binding proteins. It binds IGF-binding proteins poorly, so more of it stays free to act.^{2, 3}
• More potent despite a weaker grip. It binds the IGF-1 receptor about 3 times less well than IGF-1, yet in rats on steroids it was about 2.5 times as potent.²
• Lean tissue and gut. In those rats, IGF-1 cut muscle protein breakdown, the weight regained was mostly protein rather than fat, and IGF-1 and especially the variants raised gut weight by up to 45%.²
• Insulin-like effects. In rats with tumors, infused IGF lowered food intake, blood glucose and insulin.³ Human IGF-1 lowers blood sugar enough that its label requires dosing with a meal.⁵

We found no study that measured how long it lasts in the human body. Half-life figures quoted online are not from human data we could find.

Evidence map

Each claimed use is graded separately, because the evidence differs by use.

Scale: 5 FDA-approved, 4 strong human, 3 limited human, 2 animal or lab only, 1 anecdotal. The grades are for IGF-1 LR3, not mecasermin.

Key studies

The rat studies came from the Australian group that designed the variants.^{2, 3} Results in mecasermin can't be assumed to apply to IGF-1 LR3, which behaves differently in the body.²

By goal and route

Pick your goal to see what the evidence supports.

Sources: Increlex label,⁵ Kohler 2010,⁴ FDA compounding notice.⁸

How it's used

We don't give a dose. No human study has tested IGF-1 LR3, so no safe dose is known.

It is sold online in vials for injection.⁴ For comparison, the approved drug mecasermin is injected under the skin twice a day at a weight-based dose that starts low and rises slowly. The label says to give it within 20 minutes of a meal or snack, and to skip it if the patient can't eat, because of the risk of low blood sugar.⁵ We report this as information, not instruction.

Side effects and who should avoid it

No study has recorded IGF-1 LR3's side effects in people. The risks below are on the label of mecasermin, plain IGF-1, from trials in children.⁵ LR3 was more potent than IGF-1 in rats, so they shouldn't be assumed to be smaller.²

• Low blood sugar. 42% of children had it at least once, and 4 had seizures or lost consciousness. The label requires dosing with food.⁵
• Raised pressure in the skull. Reported in 3 of 71 children.⁵
• Swollen tonsils and adenoids. Tonsil enlargement in 15%, with snoring and ear infections among side effects.⁵
• Allergic reactions. Including anaphylaxis after approval, estimated at 0.3% of patients.⁵
• Cancer. The label warns about malignant tumors and rules out use with active cancer or a history of cancer in children.⁵
• Bones. Slipped hip growth plates and worsening scoliosis are listed warnings in growing children.⁵
• Unknown product. A doping lab found a black-market vial containing a tagged research form. Its effects in people have never been studied.⁴
• Who should avoid it. No label exists for IGF-1 LR3. Mecasermin's label rules it out with cancer or a past cancer in children, tells families to mention insulin or other diabetes medicines, and has no data in pregnancy or breastfeeding.⁵ Athletes subject to testing should avoid it.¹¹

Low blood sugar can be dangerous. Shaking, sweating, confusion or a seizure needs urgent care: call 911.

Compared with

Sources: FDA substance record,¹ Increlex label,⁵ Egrifta WR label.¹³ See our tesamorelin, sermorelin and MK-677 guides for products that raise IGF-1 through growth hormone.

Stacks

IGF-1 LR3 is often discussed alongside growth hormone releasers such as MK-677, CJC-1295 or ipamorelin. We found no study of any combination. Each raises IGF-1 activity, so the blood-sugar and growth-related risks could add up. The HHS policy covers none of these and allows one active ingredient per product.¹⁰

Myths vs evidence

All options and prices

MoveWell sells no peptides. Some links may earn us a commission; that never decides what's listed or the order. Checked November 1, 2026

Licensed compounding, with a prescription

None. IGF-1 LR3 is a protein, and FDA says biological products aren't eligible for pharmacy compounding.^{7, 8} It's also not in the HHS policy of October 28, 2026.¹⁰

Approved IGF-1

Mecasermin (Increlex) is a prescription drug for children 2 and older with severe primary IGF-1 deficiency or a growth hormone gene deletion with neutralizing antibodies. It is not a substitute for IGF-1 LR3 or for growth hormone, and it isn't approved for adults.⁵ We don't link a seller: a child's endocrinologist prescribes it.

Research use only products

We don't list sellers. These are lab reagents, and FDA treats products like them as unapproved drugs when they're meant for people. In August 2026 FDA warned five peptide sellers that a "research use only" label is no defense.¹²

Legal status history

Newest first.

1. Current statusNov 1, 2026Not FDA-approved and not approved anywhere. Not eligible for pharmacy compounding. Banned in sport at all times.^{7, 8, 11}
2. Next · no dateNo FDA review, rule or trial is scheduled that we could find.
3. Oct 28, 2026HHS enforcement discretion policy covers six peptides. IGF-1 LR3 is not one of them.¹⁰
4. Aug 24, 2026FDA warning letters to five online peptide sellers reject the "research use only" defense.¹²
5. Apr 22, 2026IGF-1 LR3 does not appear on FDA's list of compounding ingredients with safety risks or withdrawn nominations.⁹
6. Mar 23, 2020FDA's rule that chains over 40 amino acids are proteins takes effect. Biological products can't be compounded under 503A or 503B. Increlex becomes a biologics license.^{6, 7, 8}
7. 2010A German doping lab identifies tagged IGF-1 LR3 in a black-market vial.⁴
8. Aug 30, 2005FDA approves mecasermin (Increlex), plain IGF-1, for children's growth failure.⁶
9. 1992Australian rat studies report LR3 and a related variant are more potent than IGF-1.²

See every peptide's status in the regulatory tracker.

FAQ

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References