Peptides/Hormones and growth
IGF-1 LR3
Also sold as Long R3 IGF-1, Mecasermin analogue
A modified growth factor that acts at the far end of the growth hormone chain, and the most potent compound in this category.
At a glance
What people use it for
- Muscle growth and recovery
- Marketed as a growth hormone alternative
- Sold in growth hormone peptide stacks
How it is taken
Sold as a powder for injection. It is also manufactured industrially as a laboratory reagent.
Evidence
No human trials yet
Best known for
- Acts directly on the growth signal rather than asking the pituitary
- Modified to evade the binding proteins that normally hold IGF-1 in check
- Longer-acting and more potent than natural IGF-1
- Drives the PI3K/Akt/mTOR pathway, which is well characterised
IGF-1 LR3 is insulin-like growth factor 1 with two modifications: an arginine substitution and a 13 amino acid extension. Together these stop it binding to the proteins that normally hold IGF-1 in check, which makes it last far longer and act far more strongly than the natural version.
It is also, by origin, a laboratory reagent for growing cells in culture, and that remains its main industrial market.
Why people are talking about it
Because it skips the queue. Every other compound in this category asks the pituitary to release growth hormone, which then raises IGF-1, which then does the work. This one is the IGF-1, applied directly.
That directness is the appeal, and it is also why the two items in the box at the foot of this page are the most consequential on the site. Removing a hormone's natural braking system does not only amplify what you want.
What people take it for
Muscle growth, principally, and recovery. It appears in growth hormone stacks on the logic that IGF-1 is the hormone through which most of growth hormone's tissue effects actually work.
Muscle growth
The claim is more muscle, faster. The mechanism is the one part of this page not in doubt: IGF-1 activates the PI3K/Akt/mTOR pathway, which drives protein synthesis and muscle cell proliferation.
In practice that describes pushing directly on the growth signal rather than asking the pituitary to raise it. No human trial has measured muscle change in healthy adults given IGF-1 LR3.
What the evidence shows
The pharmacology is real and the modifications do what they claim. The molecule is more potent and longer-acting than native IGF-1, which is well documented in laboratory use.
There is no completed human trial of IGF-1 LR3 for muscle or recovery. Mecasermin, a different recombinant IGF-1 product, is approved for severe primary IGF-1 deficiency in children, and that approval describes a different molecule in a different population.
Other reported effects include joint pain, fluid retention and headache, which are familiar from the growth hormone axis generally.
How it is taken
Sold as a powder for reconstitution and subcutaneous injection. Protocols in circulation come from community practice, since no human dose-finding study has been done.
Its interaction with blood sugar is the practical reason timing gets discussed so much in those protocols.
How it compares
Against the growth hormone secretagogues
Ipamorelin, CJC-1295 and GHRP-6 ask the pituitary to release growth hormone, which keeps feedback control in play. IGF-1 LR3 bypasses all of that and acts at the end of the chain.
That is a difference in kind rather than in degree, and it is why this compound sits apart from the rest of its category.
Against mecasermin
Mecasermin is a licensed recombinant IGF-1, prescribed under supervision with blood sugar monitoring built into the treatment. It is the closest thing to a regulated comparison, and the monitoring is part of why it works as a medicine.
Common questions
Is it the same as IGF-1?
No. The modifications make it longer-acting and more potent by removing the natural braking system, which is both the point and the complication.
Why does it affect blood sugar?
IGF-1 has meaningful insulin-like activity, and this version evades the binding proteins that would normally buffer it.
Is there an established dose?
None in people. No human dose-finding study has been done.
Is it detectable in testing?
Yes. Growth factors are on the prohibited list in tested sport.
Last reviewed .