IGF-1 LR3 (Long R3 insulin-like growth factor 1)
IGF-1 LR3: What The Studies Actually Say
No study has ever given IGF-1 LR3 to a person. Every result comes from rats, pigs, sheep, mice and lab dishes. The same animal studies that show extra growth also show low blood sugar, faster tumor growth and a drop in the body's own growth hormone. Here is what the research actually found.
Updated 22 September 2026
Before you read this
This page explains what published studies found. That is all it is. It is not medical advice, and it is not instructions for using anything. Nothing here is meant to find, treat, cure or stop any illness. The compounds discussed on this site, retatrutide included, are not approved by the FDA for use in people. Research compounds are sold for laboratory use only — not for use in humans or animals. A study tells you what happened to the people in it. It does not tell you what would happen to you. What you do with what you read here is your responsibility, so talk to a doctor first. This page is published by Ascend Vials, which sells research compounds.
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No study has ever given IGF-1 LR3 to a person.
Everything you have heard about it comes from rats, pigs, sheep, mice and lab dishes. Here is what that research actually found. Every claim has a link. Read them yourself.
The 30-second version
- IGF-1 LR3 is a lab-made, modified copy of IGF-1, a growth signal your body makes. It was first described in 1992 as a research tool.
- No human study has ever been published. Not one trial is registered. Every result comes from animals and lab dishes.
- In rats it looked up to 6 times stronger than natural IGF-1. In other tests the edge was small, or it was weaker.
- "Long" does not mean long-lasting. In rats it left the blood about 11 times faster than natural IGF-1.
- The same animal studies found low blood sugar, faster tumor growth in rats with breast tumors, and less of the body's own growth hormone in pigs.
- It is not approved as a medicine anywhere, and it is banned in sport at all times.
- Nothing sold online has been shown to match what the studies used. No study has checked.
What it is
IGF-1 is a growth signal your body makes. IGF-1 LR3 is a lab-made version of the human one with two changes: 13 extra amino acids on the front, 11 of them copied from pig growth hormone, and one swapped amino acid at position 3. A team in Adelaide, Australia first described it in 1992, as a research tool for studying how IGF-1 works. J Mol Endocrinol, 1992
Its documented legitimate use is in the lab, as a growth ingredient for hamster cells grown to make biotech products. Morris & Schmid, 2000
Anti-doping chemists say it was never approved for human use, but it is easy to buy on the black market for bodybuilding. Drug Testing and Analysis, 2021
Not one study in a person
A 2026 clinical review put IGF-1 LR3 in its lowest evidence grade, "D." That grade means no peer-reviewed human studies. Clinical review, 2026
On September 22, 2026 we searched the US trial registry under seven spellings of the name. Zero registered trials came back. ClinicalTrials.gov
So every number below comes from an animal or a dish. That tells scientists what to test next in people. It does not tell you what happens in a person.
How it works: dodging the brakes
Natural IGF-1 docks on the IGF-1 receptor, a switch on the outside of cells, and turns on signals for growth and cell survival. LR3 is presumed to work the same way, because it uses the same receptor. Clinical review, 2026
Your body also makes IGF-binding proteins. They generally act to hold back IGF-1's signal. Exp Physiol, 2008 LR3 was built to slip past them. Natural IGF-1 grips those binding proteins about 1,000 times more tightly than LR3 does. Growth Regul, 1993
The surprise: LR3 fits the receptor itself about 3 times worse than natural IGF-1. Biochem J, 1992 Its extra punch comes from dodging the binding proteins. In chicken cells that make no detectable binding proteins, LR3 was weaker than natural IGF-1. J Mol Endocrinol, 1992
One more catch. LR3 slips past binding proteins most easily in rat blood. In human, sheep, pig and chicken blood, those proteins held on to a real share of it. J Endocrinol, 1994 Most of the big numbers below come from rats.
How much stronger? It depends on the test
| Test | Where | LR3 compared with natural IGF-1 |
|---|---|---|
| Growth, 14 days | Normal rats | 6 times stronger |
| Muscle cells in a dish | Rat cells | 5 to 10 times stronger |
| Growth in diabetic rats, 7 days | Rats | 2.5 to 3 times stronger |
| Partly undoing body breakdown from a steroid, 7 days | Rats | About 2.5 times stronger |
| Steady drip under the skin, 7 days | Rats | 1.5 to 2 times stronger |
| Undoing muscle loss, given as shots | Rats | "Barely" equal |
| Cells with no binding proteins | Chicken cells | Weaker |
Sources, top to bottom: Growth Regul, 1993 · Biochem J, 1993 · Biochem J, 1992 · J Endocrinol, 1996 · J Mol Endocrinol, 1992
Read the last column. From weaker to six times stronger, depending on the test. Any single "X times stronger" number is one experiment picked from this list. None was measured in a person.
"Long" does not mean long-lasting
The name sounds slow-release. In rats it is the opposite.
LR3 was cleared from rats' blood about 11 times faster than natural IGF-1. Most of it floated free instead of riding with binding proteins, and more of it broke down. J Endocrinol, 1993
After one injection in rats, intact LR3 disappeared quickly after about 4 hours. One breakdown piece could still be detected up to 16 hours. Drug Testing and Analysis, 2021
You may see a human half-life of 20 to 30 hours online. We could not find any study behind it. The 2026 review says its half-life is not documented. Clinical review, 2026
What it did in animals
| Study | Animal | How long | What happened |
|---|---|---|---|
| Steeb, 1994 | Rats, 6 per group | 14 days | Gut weight up 43% at the top dose |
| Tomas, 2001 | Underfed rats | 7 days | Weight 3% to 8% higher. Muscle protein not saved |
| Conlon, 1995 | Guinea pigs | 7 days | Adrenals, gut, kidneys and spleen got bigger for body size. The body did not grow |
| Dunaiski, 1997 | Pigs near market weight | 4 days | Grew more slowly and ate less |
| Dunshea, 2002 | Newborn pigs | 8 to 18 days | No effect when food was limited. Fed freely: 457 vs 386 g gained a day |
| von der Thüsen, 2011 | Mice prone to clogged arteries | Not given | Less artery narrowing, less bleeding inside plaques |
| White, 2025 | Undersized unborn lambs, 7 per group | 1 week | Did not help them grow |
| Engel, 2025 | Alzheimer-model mice, 19 to 27 per group | 7 months | Some brain plaques changed. Memory and thinking tests did not |
Read the last column. The gut grew almost everywhere it was measured. Muscle is the weak spot. In underfed adult rats, LR3 made muscle breakdown worse and muscle building slower. Growth Horm IGF Res, 2001 Given as shots, it was only "barely" equal to natural IGF-1 at undoing muscle loss. J Endocrinol, 1996
None of these animals is a person. Nobody knows whether the results carry over.
What the ads leave out
Low blood sugar. In pigs given one injection, LR3 and similar IGF-1 variants lowered blood sugar 2 to 3 times more strongly than natural IGF-1. Over 4 hours the total drop was about 4 to 8 times bigger. J Endocrinol, 1997 Reports from people using it outside studies center on insulin-like effects, such as signs of low blood sugar. Many come from outside any clinic. Clinical review, 2026
Tumor growth. In rats with a breast tumor, 6 to 7 days of IGF-1 made the tumors grow more, LR3 most of all. In a dish, the same peptides did not make those tumor cells grow. Biochem J, 1994 In human prostate cancer cells, LR3 raised telomerase, an enzyme that helps cancer cells keep dividing, about 3-fold. J Clin Endocrinol Metab, 2003 In human breast cancer cells, it drove growth about as much as insulin did. Eur J Cancer, 1996
The 2026 review calls long-term cancer risk from LR3 theoretical but clinically relevant. Clinical review, 2026
Your own hormones. In pigs, 4 days of LR3 cut average growth hormone by 23% and the area under its pulses by 60%. It also lowered their own IGF-1 and insulin. J Endocrinol, 1997
The approved cousin. The closest thing to human safety data is for a different molecule: mecasermin (Increlex), a copy of natural human IGF-1. In its studies of 71 children, 42% had low blood sugar at least once, and 4 had seizures or passed out from it. Its label also warns about cancers reported in treated children, though nobody knows whether the drug caused them. FDA label, 2025 That is not LR3. LR3 has never been tested for any of this in people.
Is it approved?
No. IGF-1 LR3 is not an approved medicine anywhere. Anti-doping chemists say it was never approved for use in humans. Drug Testing and Analysis, 2021
- US. Not FDA-approved. The IGF-1 drug on the market is mecasermin (Increlex), for children who are not growing because of a severe lack of IGF-1 or a rare growth-hormone gene problem. FDA label, 2025 A second approved IGF-1 drug, Iplex, is listed as discontinued. Drugs@FDA Neither is LR3.
- EU. Not authorised. Increlex is authorised there under "exceptional circumstances." EMA
- Australia. The June 2026 Poisons Standard lists insulin-like growth factors as prescription-only, and illegal to possess without authority. LR3 is not named on its own, but the entry appears to cover it. That is our reading, not an official ruling. Poisons Standard, 2026
- Sport. The World Anti-Doping Agency's 2026 list bans IGF-1 "and its analogues," at all times, in and out of competition. WADA 2026 list
Other countries we have not checked against official sources.
What is still unknown
- Whether it does anything in people, including building muscle or cutting fat.
- How long it lasts in a person, and whether the rat numbers carry over.
- The low-blood-sugar risk at amounts passed around on bodybuilding forums. Those are user reports, not tested doses.
- Long-term cancer risk. No person has ever been followed.
- Whether the body makes antibodies against the pieces copied from pig growth hormone.
- Safety in pregnancy, in diabetes, or alongside insulin.
What is in the bottle is not what was studied
One more thing.
Every result on this page came from lab LR3 in cells and animals. None of it tested a product sold online. Doping labs have looked at some of what is sold:
- The Cologne doping lab found an injection vial holding a lab-purification version of LR3, with a "His-tag" still attached. Its effects in humans have never been described. Source
- Seized products the same lab analysed in 2009 included unpurified LR3. Source
- French anti-doping chemists found plenty of signs of lower-quality, oxidized peptide in black-market products. Drug Testing and Analysis, 2021
No study has ever shown that a product sold online as "IGF-1 LR3" is the same thing the studies used. Not the same purity. Not the same strength. Not even proof it is the same molecule.
So take every number on this page for what it is. It describes lab LR3 in cells and animals. It describes nothing else.
How to check a number yourself
You are going to see more claims about IGF-1 LR3. In a reel. In a comment. On somebody's store page.
Here is how to tell a real one from a marketing one. Five questions. About ten seconds each.
1. Is there a link to a study?
A real number comes from a paper you can open. No link means it is a claim, not a result. Search the name on pubmed.gov yourself. If nothing comes back, nothing was published.
2. Was it done in people?
For LR3 the answer, so far, is always no. Look for "rats," "pigs" or "cells" near the top of the paper. An animal result is a reason to run a human study. It is not a human result.
3. Which animal?
LR3's biggest numbers come from rats. Rat blood is where it slips past binding proteins most easily.
4. Stronger at what?
"Times stronger" needs three answers: than what, at doing what, and in which animal. On this page the same molecule ranged from weaker to six times stronger.
5. Where does the half-life come from?
"Long" sounds long-lasting. In rats, LR3 was cleared about 11 times faster than natural IGF-1. If someone quotes a human half-life, ask for the study. We could not find one.
Now run those five on this page
Every number above links to its paper and names the animal or cells. The potency table shows every result, not just the best one. The risks sit right next to the gains.
Any claim about what LR3 does in a person has no human study to link to. None has been published.
That is the whole difference: a number you can check, and a number you are asked to believe.
This page has a date on it, near the top. If a human study of IGF-1 LR3 is ever published, this page changes.
Read the studies yourself
- Clinical review, 2026 — the main one: no human studies, half-life not documented
- ClinicalTrials.gov search — no registered trials
- Where it came from: Francis, J Mol Endocrinol 1992 · Morris & Schmid 2000
- How it works: Ballard, Growth Regul 1993 · Tomas, Biochem J 1992 · Lord, J Endocrinol 1994 · Gehrig, Exp Physiol 2008
- How fast it clears: Bastian, J Endocrinol 1993 · Mongongu, Drug Test Anal 2021
- Rats: Tomas, Biochem J 1993 · Tomas, J Endocrinol 1996 · Tomas, Growth Horm IGF Res 2001 · Steeb, Am J Physiol 1994
- Other animals: Tomas, J Endocrinol 1997 · Dunaiski, J Endocrinol 1997 · Dunshea, Br J Nutr 2002 · Conlon, J Endocrinol 1995 · von der Thüsen, Am J Pathol 2011 · White, Am J Physiol 2025 · Engel, J Alzheimers Dis 2025
- Cancer: Tomas, Biochem J 1994 · Wetterau, J Clin Endocrinol Metab 2003 · Vink-van Wijngaarden, Eur J Cancer 1996
- What is actually sold: His-tagged vial · 2009 seizures
- The rules: Increlex FDA label · Iplex, Drugs@FDA · Increlex, EMA · Poisons Standard, Australia · WADA 2026 list
Everything above about IGF-1 LR3 describes lab and animal experiments. None of it was done in people. The mecasermin figures describe a different, approved drug. This is not advice, a plan, or instructions. IGF-1 LR3 is not an approved medicine. Research compounds are not for human or animal use.