IGF-1 LR3

DNot approved; research reagentGrowth hormone, IGF-1 and growth factors →Long R3 IGF-1LR3 IGF-1insulin-like growth factor 1 analogue
In one paragraphIGF-1 LR3 is a modified version of insulin-like growth factor 1, engineered so that it evades the binding proteins that normally control IGF-1 and therefore stays active far longer. It was designed as a cell-culture reagent for laboratories, not as a medicine, and no controlled human trial has ever tested it. Natural IGF-1 is available as an approved drug, mecasermin, for a rare severe deficiency — the LR3 analogue is a different molecule with no clinical file at all.
Schematic 3D structure of IGF-1 LR3
83 residues · IGF-1 with a 13-residue N-terminal extension · schematic
Overall gradeD No human evidence
Human trials0 controlled
Outcomes graded3
Last reviewed3 September 2026
EvidenceWhat it isHow it worksUnknownsMolecule & PKRegulationQuestionsReferences

What the human research shows

One of the clearest cases on this site of a laboratory tool being sold as a physique drug. The parent hormone is well characterised and even approved for a narrow indication; the analogue people actually inject has never been given to a human in a trial.

MetabolicCardioMuscleHealingNeuroImmuneSexualSkinAgeing

Evidence profile0–5

  • Metabolic & weight—0.0
  • Cardiovascular—0.0
  • Muscle & growth—0.0
  • Healing & repair—0.0
  • Neuro & sleep—0.0
  • Immune & inflammation—0.0
  • Sexual & hormonal—0.0
  • Skin & appearance—0.0
  • Ageing & longevity—0.0
No benefit outcome for IGF-1 LR3 has both human evidence and a measurable effect, so the profile is empty. That is the finding, not a gap in the chart.
OutcomeGradeEffect sizeHuman studiesWhere the evidence comes from
Muscle growthDNo human evidenceNot measurable0 controlledNo controlled human trial of IGF-1 LR3 exists for muscle, strength or body composition. The claims extrapolate from IGF-1's known role in tissue growth and from animal and cell work.
Any clinical outcomeDNo human evidenceNot measurable0 controlledA PubMed search for the compound and its aliases returns recombinant-expression papers, rodent studies and reviews of self-administration — no human trial.
Safety in humansadverseDNo human evidenceNot measurableNoneNo human dosing study exists. The theoretical concerns are hypoglycaemia, because IGF-1 has insulin-like activity, and the long-term effect of sustained growth signalling — neither measured in people for this analogue.1
AMultiple good human trials, consistentBSome human trials, mostly consistentCFew or weak human studiesDAnimal or anecdotal onlyeffect size · red = adverse

Literature searched to 3 September 2026. Human studies only; animal and cell work informs the mechanism section and nothing else.

What it is

IGF-1 is the hormone through which growth hormone does most of its work. In the body it is almost entirely bound to carrier proteins that regulate how much is active at any moment. LR3 is an analogue with an extra 13-amino-acid extension and a substitution that together stop it binding those carriers.

That modification is useful in a culture flask, where a long-lasting growth signal is convenient. It is exactly what makes the molecule uncontrolled in a person, and it is why the compound was never developed as a medicine.

How it is thought to work

It activates the IGF-1 receptor, and unlike natural IGF-1 it is not restrained by binding proteins. It also has meaningful affinity for the insulin receptor, which is the basis of the hypoglycaemia concern. None of this has been characterised in humans for this analogue.

What is still unknown

  • Whether it does anything to muscle in a person.
  • Dose, half-life and safety in humans — none established.
  • The long-term consequences of unregulated IGF-1 receptor signalling.

The molecule and how long it lasts

Identity

An 83-residue protein analogue; not in PubChem Compound at review

Pharmacokinetics
Route
Injected as sold; no human study (mecasermin is a different, approved product)
Half-life
No human pharmacokinetic data

No pharmacokinetic study in people.

Regulatory status

European Union
Unauthorised medicinal product

No marketing authorisation. Sold as a research reagent; supplying it for human use is an offence under national medicines law.

United States
Not approved

Not an approved drug. Mecasermin (recombinant human IGF-1) is approved for severe primary IGF-1 deficiency; the LR3 analogue is a different, unapproved molecule.

United Kingdom
Unlicensed medicine

No MHRA licence; supply for human use is an offence.

Australia
Prescription-only / unapproved

Not on the ARTG; imports are seized.

Canada
Not authorised

No Drug Identification Number.

Sport (WADA)
Prohibited at all times

IGF-1 and its analogues are prohibited in and out of competition as growth factors.

Questions people actually ask

Does IGF-1 LR3 build muscle?
No controlled human trial has tested it. Every claim rests on IGF-1's known biology and on animal work, not on evidence in people.
Is it the same as the approved IGF-1 drug?
No. Mecasermin is recombinant human IGF-1, approved for a rare severe deficiency. LR3 is a modified analogue built to evade the body's control mechanisms, and it has no approval or clinical trial anywhere.
Why is it sold as 'research use only'?
Because that is what it was made for — a cell-culture reagent. The label is not a loophole that makes human use lawful or studied.

One page per claimed effect

References

  1. 1
  2. 2

Change log

  • 2026-09-03Initial publication. All outcomes graded D on the absence of any human trial of the LR3 analogue.