IGF-1 LR3

A supercharged version of the growth factor GH works through. It is potent, long-acting and unforgiving if you dose it fasted.

Evidence: DCommunity use what's this?
Grade D. The IGF-1 mechanism is proven through mecasermin, but LR3 itself has almost no human data.
Also known as: Long R3 IGF-1 · Insulin-like Growth Factor 1 Long Arg3
Class: Synthetic long-acting analogue of IGF-1 (83 amino acids)

The 30-second version

WhatIGF-1 with a 13-amino-acid extension and an Arg3 swap, so binding proteins can’t neutralise it.

Why people use itMuscle growth, recovery and holding gains after a cycle.

The honest catchLow blood sugar is a same-day danger, and growth signalling is a long-term cancer concern.

What it is

Much of what growth hormone does, it does through IGF-1 made in the liver. Natural IGF-1 lasts only 12–15 minutes, because carrier proteins (IGFBPs) grab it. LR3’s modifications stop that binding, so it stays active for roughly 20–30 hours and hits harder per dose. Unmodified IGF-1 is approved as mecasermin (Increlex) for children with severe IGF-1 deficiency. LR3 is the bodybuilding analogue: not approved and barely studied in peer-reviewed work.

How it works

IGF-1 receptor on muscle, bone, fat and many other cells, and it stays bound far longer than natural IGF-1.

PI3K–Akt–mTOR. More muscle protein synthesis and less breakdown.

Insulin-like. The same pathway pulls glucose out of the blood, which is the source of the hypoglycaemia risk.

RAS–MAPK. Cell division and satellite-cell activation, and possibly new muscle fibres.

The trade. Strong anabolic signalling now, with a theoretical tumour-growth concern over time.

What the research shows

For LR3 itself: almost nothing in humans. It was developed as a potent cell-culture reagent, which is where its characterisation comes from. For the IGF-1 mechanism: mecasermin has real trial and registry data showing it restores growth in severe IGF-1 deficiency, and it clearly documents the side effects, especially hypoglycaemia^1,2,3.

More is not better. Above about 40 mcg the receptor saturates, so extra dose mostly adds side effects.

Evidence at a glance

Use	Grade	Best evidence	Main gap	Read
IGF-1 mechanism	AApproved	Mecasermin restores growth^1,3	Native IGF-1, not LR3	Proven
Muscle growth (LR3)	DCommunity use	Community reports	No human trial	Plausible
Hyperplasia	ELab & animal	Satellite-cell activation possible	Not shown in humans	Speculative
Long-term safety	ELab & animal	None for LR3	Cancer and glucose concerns	Unknown

Dosing: what has been reported

Not a recommendation. These figures describe what was studied or what circulates in practice, kept separate so you can see how solid each one is. Speak with a qualified clinician before acting on any of it.

Setting	Figure	Route	Grade
Approved native IGF-1	Mecasermin 40–80 mcg/kg twice daily, max 120 mcg/kg, always with a meal¹	Subcutaneous	A
Community, beginner	10–20 mcg/day, 4–6-week cycles	SC or IM	D
Community, common	20–50 mcg/day, after training with food	SC or IM	D
Community, advanced	50–100 mcg/day: higher risk, little extra benefit	SC or IM	D

Three rules apply to all community protocols: always dose with or straight after a carbohydrate meal, never fasted; never before bed, because low blood sugar during sleep is hard to catch; and cap cycles at 4–6 weeks, because continuous use downregulates the receptor. Keep a glucose meter on hand.

Preparing & storing

Reconstitute with bacteriostatic water. Some prefer dilute acetic acid for better stability. It’s more delicate than small peptides: store the powder cold, refrigerate once mixed and never shake it.

Reported side effects

Hypoglycaemia: shakiness, sweating, confusion; worst when dosed fasted or at night
Water retention and puffiness
Joint pain at higher doses; headaches
Injection-site reactions
Excess dosing: unwanted tissue or organ growth (an acromegaly-like concern)
Long term: insulin resistance and a theoretical cancer risk

Who should avoid it

Active or past cancer (strongly)
Diabetes or a tendency to low blood sugar
Insulin users: the most dangerous combination
Proliferative eye disease; pregnancy and breastfeeding
Tested athletes: WADA prohibited, detectable

Regulatory status checked Oct 2026

Body	Status	Detail
FDA (US)	Not approved	Research chemical; native IGF-1 (mecasermin) approved for a narrow deficiency.
EMA (EU)	Not approved	Mecasermin approved; LR3 is not.
CDSCO (India)	Not approved	No approval identified for the analogue.
WADA	Prohibited	IGF-1 and analogues are banned at all times.

The NexGen read

Potent, and its potency is the risk

IGF-1 LR3 is the strongest anabolic signal in this section. It also comes with an immediate hypoglycaemia risk, a long-term cancer question and no human safety data of its own. It is not for beginners, fasted dosing or anyone with a cancer history.

References

Increlex (mecasermin) prescribing information. FDA-approved 2005 for severe primary IGF-1 deficiency.
Bang P, Polak M, Woelfle J, Houchard A. Effectiveness and safety of rhIGF-1 therapy in children: the European Increlex Growth Forum Database. Horm Res Paediatr. 2015;83(5):345–357.
Profile of mecasermin for long-term treatment of growth failure in severe primary IGF-1 deficiency. PMC2724186.