IGF-1 LR3
Modified insulin-like growth factor 1 · Long R3 IGF-1. Related compounds sold as IGF-1 DES and PEG-MGF
- UK status
- Unlicensed medicine
- Availability
- Research use only
- Evidence base
- No human trials of the modified analogue
- Controlled drug
- No
Sequence
A modified form of IGF-1, 83 amino acids, with an extended N-terminus and a substitution at position 3.
The short version
What it does
Sold for muscle growth. It is the downstream signal that growth hormone works through, so the pitch is that it skips a step and acts directly.
How it does it
Growth hormone mostly works by making your liver produce IGF-1, which is what actually tells tissue to grow. This is a modified version of IGF-1 built to survive in the body far longer than the natural one.
The catch
It is structurally close to insulin and can lower blood sugar dangerously. It also tells tissue to grow without asking what kind, which is why raised IGF-1 is studied in connection with cancer risk. There are no human trials of the modified version at all.
Everything below goes into the detail, with sources.
Most compounds in this register carry the risk of doing nothing. This one carries the risk of doing something, and the two most plausible somethings are a hypoglycaemic episode and a growth signal you cannot direct.
At a glance
- Compound type
- Modified IGF-1, 83 amino acids
- Also written
- Long R3 IGF-1
- What the modification does
- Escapes the carrier proteins that normally hold IGF-1 inactive
- Originally developed as
- A cell culture reagent, not a human medicine
- Marketed for
- Muscle growth
- Acute risk
- Hypoglycaemia. It has meaningful insulin receptor activity.
- Unresolved risk
- Cancer. Raised IGF-1 is associated with increased risk in observational studies.
- Licensed relative
- Mecasermin, for severe primary IGF-1 deficiency in children
- UK status
- Unlicensed medicine. Supply for human use prohibited.
- In sport
- Prohibited at all times under WADA S2.1, growth factors.
01What it is
Insulin-like growth factor 1 is the hormone that mediates most of what growth hormone does. Growth hormone travels to the liver, the liver produces IGF-1, and IGF-1 acts on tissue. If you want the tissue effect, IGF-1 is the more direct lever, which is the entire logic of selling it.
Natural IGF-1 clears from the blood in minutes because it is bound and regulated by carrier proteins. Long R3 IGF-1 is modified in two ways to defeat that: an extended chain at one end and a substituted amino acid at position 3, which together greatly reduce binding to those carriers and extend how long it circulates.
The carrier proteins are not an inconvenience. They are the control system, holding IGF-1 inactive until and where it is wanted. A version engineered to escape that control is a version whose activity nobody is regulating, including your body.
02How it came about
Recombinant human IGF-1 is a real medicine. Mecasermin is licensed in some jurisdictions for severe primary IGF-1 deficiency, a rare condition in children, and it is prescribed under specialist supervision with careful attention to blood glucose.
Long R3 IGF-1 is a different molecule, developed as a research reagent for cell culture work, where a long-acting IGF-1 is useful in a flask. It was never developed as a human medicine, and its appearance in bodybuilding supply predates most of the current peptide market.
03UK legal and licensing status
IGF-1 LR3 has no marketing authorisation anywhere for human use. Supplying it for human use in the UK is prohibited under the Human Medicines Regulations 2012. It is not a controlled drug under the Misuse of Drugs Act. It is sold as a research chemical, and in this case that description is closer to true than usual: it genuinely is a cell culture reagent.
Athletes: WADA prohibits IGF-1 and its analogues under S2.1, growth factors and growth factor modulators. Prohibited at all times. Detection methods for IGF-1 analogues exist.
04How it works
It binds the IGF-1 receptor, activating pathways that drive cell growth, protein synthesis and division, and it inhibits cell death. In muscle that means a genuine growth signal.
It also has meaningful affinity for the insulin receptor, because IGF-1 and insulin are structurally related. That is not a footnote. It is the mechanism behind the most immediate danger.
05What it is not
Claims that attach themselves to this compound and do not hold up.
- Not mecasermin. Licensed IGF-1 exists for a rare deficiency in children, under specialist care with glucose monitoring. That is a different molecule used in a different situation.
- Not a tested human compound. There are no human trials of Long R3 IGF-1. It was made as a laboratory reagent.
- Not a targeted muscle builder. The receptor is on tissue throughout the body. You cannot aim a systemic growth signal.
- Not comparable in risk to the rest of the shelf. Most compounds here risk wasting your money. This one has a plausible route to an acute medical emergency.
06What the evidence shows
IGF-1 biology is thoroughly established. It is one of the better understood growth factors in human physiology, and there is no serious doubt that it drives tissue growth.
There are no human clinical trials of Long R3 IGF-1 for muscle growth, or for anything else. The mechanism is real and the product is untested, which is the worst combination in this register: strong enough to do something, with nobody having established what.
Separately, the epidemiological literature associates higher circulating IGF-1 with increased risk of several cancers. That is association in observational data, not proof that injecting it causes cancer, and it should not be overstated. It is also exactly the concern you would expect from sustained elevation of a growth signal, and it is unresolved.
All human safety data. The specific unresolved questions are hypoglycaemia risk, effects on tissues other than muscle, and long-term cancer risk from sustained IGF-1 elevation.
07Reported harms
No regulated frequency table exists. The recognised concerns, drawn from IGF-1 physiology and from licensed mecasermin use, are:
- Hypoglycaemia. Low blood sugar, potentially severe. This is the acute risk and it is the reason licensed IGF-1 use involves glucose monitoring and food timing under supervision. Severe hypoglycaemia can cause seizures, loss of consciousness and death.
- Unwanted tissue growth. The receptor is not confined to muscle. Effects on other tissues, including organ growth, are described with growth factor excess generally.
- Cancer risk. Unresolved, and the reason for genuine caution rather than alarm. Raised IGF-1 is associated with increased risk of several cancers in observational studies.
- Unregulated supply. Unverified identity and concentration, which for a compound that can cause hypoglycaemia is a materially worse problem than for an inert one.
08Interactions and cautions
Insulin and any glucose-lowering medication are the critical ones. Combining a compound with insulin receptor activity and a diabetes medicine, with no dose established and no monitoring, is the scenario that puts people in hospital. Anyone with diabetes should read that sentence twice.
09Stopping
Circulating levels fall and the growth signal ends. Nothing else is documented.
10Monitoring
Nothing is monitored outside licensed mecasermin use, where glucose monitoring is central. If anyone were being sensible, blood glucose would be the priority, and vendors do not mention it.
11Questions worth asking
Take these to a doctor or pharmacist. A good clinician will not mind being asked, and the answers are specific to you in a way nothing on this page can be.
- Do I understand this can cause low blood sugar, and would I recognise it happening?
- Do I have diabetes or take anything that lowers blood glucose?
- Am I comfortable with an unresolved cancer question, given nobody can quantify it?
- If I compete in a tested sport, do I know this is prohibited at all times?
12Common questions
Is IGF-1 LR3 legal in the UK?
It has no marketing authorisation for human use, so supplying it for human use is prohibited. It is not a controlled drug. It can be sold lawfully as a laboratory reagent, which in this case is genuinely what it was developed as.
Is it more dangerous than other peptides?
It carries a different kind of risk. Most compounds in this register risk doing nothing. This one has meaningful insulin receptor activity, so it can lower blood sugar, and severe hypoglycaemia is a medical emergency. That is a real acute risk rather than a theoretical one.
Does IGF-1 cause cancer?
Unresolved, and worth stating carefully. Observational studies associate higher circulating IGF-1 with increased risk of several cancers. Association is not proof of causation, and nobody has established what injecting a long-acting analogue does. It is a reason for genuine caution, not a claim that it causes cancer.
Isn't IGF-1 a real medicine?
Mecasermin, recombinant human IGF-1, is licensed in some countries for severe primary IGF-1 deficiency in children, under specialist supervision with glucose monitoring. Long R3 IGF-1 is a different, modified molecule that was never developed for human use.
13Sources
Links go to the authoritative source. Where a document sits behind a paywall or moves around, the full citation is given so you can find it yourself.
- Prohibited List, S2.1 growth factorsWADA
- IGF-1 physiology and the IGF binding proteinsPubMed
- Mecasermin prescribing informationFDA
- Circulating IGF-1 and cancer risk, observational literaturePubMed
- Unlicensed medicines guidanceMHRA
Get told when something changes
A short email when a licence changes, a safety alert lands, or a trial reports. No selling, no advertising, no sharing your address. Unsubscribe whenever.
14Change history
Every substantive change to this record is logged here with its date. Corrections are made openly, not quietly.
Loading…
Want telling when this record changes? Follow it from your account.