IGF-1 LR3 Review: Benefits, Weight Loss, Side Effects and Research (2026)

IGF-1 LR3 (Long R3 IGF-1) is a lab-made version of insulin-like growth factor 1, the hormone that carries many of growth hormone’s effects. It has an extra stretch of 13 amino acids and an arginine at position 3, so it binds the IGF-binding proteins poorly and circulates mostly free. That made it more potent than IGF-1 in animal studies. It was made for cell culture and animal research and has never been tested in humans; in pigs it lowered blood sugar more than IGF-1 and suppressed growth hormone. It is not approved anywhere, and WADA bans it.

This review merges our older IGF-1 LR3 guides and checks each claim against the studies. It is not the same molecule as mecasermin (Increlex), the only approved IGF-1 drug.

What is IGF-1 LR3?

Natural IGF-1 has 70 amino acids. IGF-1 LR3 has 83: a 13-amino-acid extension at the start and an arginine at position 3. Normally, most IGF-1 in the blood is bound to IGF-binding proteins, which hold it in check; LR3 escapes most of that binding, so more of it is free to act. It is widely sold as “IGF-1 LR3 1 mg” vials of freeze-dried powder for injection.

How does it work?

Like IGF-1, it activates the IGF-1 receptor, which drives growth and protein building in muscle and other tissues, and it has insulin-like effects on blood sugar. Because it is mostly unbound, its effects in animals were stronger, but in rats it was also cleared from the blood several times faster than IGF-1. In pigs, it shut down the body’s own growth hormone and IGF-1, the same kind of feedback that suppresses natural testosterone when people take testosterone.

What the research shows

There is no human study of any kind. Everything said about IGF-1 LR3 in people, whether muscle growth, fat loss or recovery, is extrapolated from these animal studies or from what natural IGF-1 does.

IGF-1 LR3 benefits: what is and isn’t shown

IGF-1 LR3 for weight loss

IGF-1 LR3 is often searched for weight loss, but there is no evidence for it. No human study exists, and the animal studies looked at muscle, growth and blood sugar. In pigs it lowered food intake and growth, together with a strong drop in blood sugar, which is not a safe or proven route to fat loss. If fat loss is the goal, see best SARMs for cutting for what the evidence shows, and peptides for weight loss.

IGF-1 LR3 vs IGF-1

While many online sources will tell you that the two compounds above are similar, there are some important differences between them.

IGF-1 has 70 amino-acids in total, while IGF-1 LR3 has a total of 83.

LR3 binds the IGF-binding proteins poorly. That makes more of it free to act, but in rats it was cleared from the blood several times faster than IGF-1, so the common claim that it lasts “20 hours or more” in people is not backed by any study.

In steroid-treated rats it was about 2.5 times more anabolic than IGF-1 when infused, but injected it barely matched IGF-1.

The approved IGF-1 drug, mecasermin (Increlex), is native-sequence IGF-1 for children with severe primary IGF-1 deficiency; its label lists low blood sugar in 42% of trial patients.

IGF-1 LR3 half-life

It has not been measured in humans. In rats, it was cleared from the blood several times faster than IGF-1, because it circulates mostly unbound. Figures of 20–30 hours quoted online do not come from a published study.

Dosing

We do not give personal doses. There are no human dosing studies, and animal doses do not translate to people. The microgram schedules seen online are not based on any trial.

IGF-1 LR3 side effects

Low blood sugar (hypoglycemia)

The best-documented risk. In pigs, IGF-1 variants like LR3 lowered blood sugar more and for longer than IGF-1. The approved IGF-1 drug lists hypoglycemia in 42% of trial patients. Symptoms include shakiness, sweating, confusion and, if severe, fainting or seizures.

Growth hormone and IGF-1 suppression

In pigs, LR3 lowered growth hormone and the body’s own IGF-1. Effects on testosterone were not reported.

Cancer

No study has tested LR3 and cancer. IGF-1 signaling drives cell growth, and the approved IGF-1 drug’s label reports cancers in children treated with it, which is why caution is usually advised for anyone with a current or past cancer. Whether this applies to LR3 is not established.

Other IGF-1 class effects

The mecasermin label also lists raised pressure in the skull and enlarged tonsils and adenoids. “GH gut” and organ growth are discussed online for growth-hormone users; no study has examined them with LR3.

Product identity

Black-market products have been found to contain a His-tagged research version of LR3 and oxidized (degraded) peptide forms.

Is IGF-1 LR3 legal?

It is not an approved drug in the US (no Drugs@FDA application); the only approved IGF-1 medicine is mecasermin, a different molecule. In Australia it falls under the Schedule 4 entry for insulin-like growth factors, and possession without authority is illegal. In sport, WADA bans IGF-1 and its analogs at all times (S2.3), and anti-doping labs have a validated blood test for LR3 and its breakdown products.

Where to buy IGF-1 LR3

Because black-market vials have been mislabeled or degraded, a batch-specific certificate of analysis is the minimum. Sarmguide’s pick is SwissChems, which sells IGF-1 LR3 as 1 mg vials and publishes independent test results. See the lab tests guide for how to check a peptide COA.

Conclusion

IGF-1 LR3 is a research reagent with a strong animal profile and no human data. In animals it was anabolic but also lowered blood sugar, cut growth hormone and, in pigs, reduced growth. There is no evidence for fat loss, and its half-life in people is unknown. It is banned in sport and not approved anywhere. Related: MK-677 · CJC-1295 · peptides for bodybuilding