Animal protein-metabolism study
An intravenous LR3 study examined protein metabolism in beef heifers. It cannot answer human physique, recovery or safety questions. [1]
Compound evidence dossier · O-008
IGF-1 LR3: claims, risk, and sport status
A modified growth-factor analogue promoted for muscle and recovery. Direct human outcome evidence is missing, so risks from approved IGF-1 medicines must be labelled as class context.
What does the evidence say?
IGF-1 LR3 is a modified, longer-acting IGF-1 analogue with no reliable human trial evidence for muscle gain, recovery or performance. The identifiable published administration study is in cattle, not people. Serious risks are biologically plausible and informed by the approved recombinant IGF-1 medicine mecasermin, but exact frequencies and effects cannot be transferred to LR3 without direct human data.
Claim check
Which claims survive an evidence check?
Each row keeps the claim, its best supporting evidence and the limiting caveat together.
IGF-1 LR3 is the same as medical IGF-1Incorrect
LR3 is a modified analogue designed to have reduced binding to IGF-binding proteins and prolonged activity. Mecasermin is recombinant human IGF-1 with an authorised paediatric indication; its label is context, not proof of LR3 equivalence.
It builds muscle in humansNot demonstrated
The commonly identifiable LR3 administration paper studied protein metabolism in beef heifers. Animal anabolic findings cannot establish human muscle gain, performance or safety. [1]
It avoids growth-hormone pathway risksMisleading
Direct growth-factor action creates its own risk questions. Approved IGF-1 labelling includes severe hypoglycaemia and warnings concerning intracranial hypertension and malignant neoplasia. LR3-specific rates are unknown. [2]
A longer half-life means a better resultUnsupported
Longer exposure is a pharmacokinetic property, not a patient benefit. It may also prolong unwanted biological effects; human LR3 outcome and safety studies are missing.
Human evidence
What have studies in people shown?
The evidence gap is sharper than for a secretagogue with human hormone-challenge studies. Published LR3 administration evidence identified for the promoted outcome is animal research.
Approved mecasermin is different
Mecasermin provides a well-developed warning set for recombinant human IGF-1, including severe hypoglycaemia and neoplasia concerns. The product and population differ from LR3. [2]
Enforcement is not efficacy
An FDA warning letter records IGF1-LR3 among compounded products at a facility with serious sterile-production and manufacturing violations. It documents product risk, not clinical benefit. [3]
Critical distinction
Direct evidence versus growth-factor class inference
The safest wording states which facts concern LR3 itself and which come from related, authorised IGF-1 treatment.
- Directly supported for LR3
- Modified analogue; reduced binding-protein affinity is part of its research rationale; animal administration studies exist.
- Not directly established
- Human dose-response, muscle gain, recovery, performance, adverse-event rates and long-term outcomes.
- Class-linked context
- Hypoglycaemia, tissue-growth effects and intracranial hypertension are clinically important in approved IGF-1 treatment.
- Required caveat
- Those labelled risks support concern, but exact severity and frequency for LR3 cannot be claimed without LR3 human data.
Risk register
What could go wrong?
The absence of direct human safety data increases uncertainty. It does not reduce the biological stakes of prolonged growth-factor signalling.
| Risk channel | Evidence-aware interpretation |
|---|---|
| Class-linked acute risk | Severe hypoglycaemia is a boxed warning for mecasermin. LR3-specific incidence is unknown, and longer action could complicate an adverse effect. |
| Growth-related concern | Approved IGF-1 labelling addresses malignant neoplasia and tissue-growth effects. Applying exact rates to LR3 would be unjustified. |
| Product quality | Unapproved sterile injectables can fail identity, strength, sterility, endotoxin and stability requirements. |
| Unknowns | Interactions, cardiovascular effects, repeated-use outcomes and risk in people with cancer, diabetes or other health conditions are not defined for LR3. |
Product evidence
What would evidence about a vial prove?
A compound-level literature verdict and a product-level finding answer different questions. Neither can substitute for the other.
Claimed compound
The literature applies only if the vial contains the same active substance and form that the source studied.
Label and release record
A batch-specific record should identify the material, method, result, specification and accountable laboratory.
Submitted sample
A defensible result concerns the sample tested. It does not certify every vial, future batch or storage condition.
Clinical meaning
Identity, purity and sterility evidence cannot establish a health outcome or fill a missing human safety dataset.
Status check
Is it authorised or prohibited?
Medicine authorisation, lawful supply and anti-doping status are separate checks. Each can change and should be verified at the point of decision.
| System | Finding checked 8 August 2026 |
|---|---|
| UK medicine status | No IGF-1 LR3 medicine with a UK marketing authorisation was identified. This should not be confused with authorised mecasermin products containing recombinant human IGF-1. |
| United States | IGF-1 LR3 is not an FDA-approved medicine. FDA enforcement records document it among ineligible compounded sterile products at one inspected facility. |
| Sport | IGF-1 and its analogues are prohibited at all times under the 2026 WADA list. WADA-funded detection research names LONG R3 IGF-1 as an analogue of anti-doping interest. |
Method note
How was this judgement made?
We searched for direct human LR3 administration studies before using the mecasermin label. Approved-IGF-1 risks were marked as class-linked context, and no exact rate was transferred to LR3.
Searches prioritised regulator documents, current medicine and anti-doping records, trial registrations and indexed primary studies. Seller pages were not used as evidence of efficacy or safety.
Read the full editorial method and inspect the evidence library.
Source ledger
Primary sources
- Hill et al., long R3 IGF-1 and protein metabolism in beef heifersAnimal administration study; no human outcome evidence. Checked 8 August 2026.
- US FDA, INCRELEX (mecasermin) prescribing informationApproved recombinant human IGF-1 label used only for class-linked risk context. Checked 8 August 2026.
- US FDA warning letter, Tailor Made CompoundingManufacturing and sterile-product enforcement record that includes IGF1-LR3. Checked 8 August 2026.
- WADA research, detection of human IGF-1 and LONG R3 IGF-1Official anti-doping research resource naming the analogue. Checked 8 August 2026.
- World Anti-Doping Agency, 2026 Prohibited ListCurrent list used for sport-status checks; effective 1 January 2026. Checked 8 August 2026.
- MHRA ProductsPublic UK medicines database used for the marketing-authorisation check. Checked 8 August 2026.
Questions answered
Frequently asked questions
Short answers keep the decisive caveat beside the claim.
What is IGF-1 LR3?
It is a modified insulin-like growth factor 1 analogue designed to bind less strongly to IGF-binding proteins and remain active for longer. It is not the same product as authorised recombinant human IGF-1.
Has IGF-1 LR3 been tested for muscle gain in humans?
No reliable human outcome trial was identified. A frequently found LR3 administration paper concerns protein metabolism in beef heifers, so it cannot establish human muscle or performance benefit.
Can mecasermin side effects be applied to LR3?
They provide serious class-linked context, including hypoglycaemia and growth-related warnings. Exact rates and effects cannot be transferred because LR3 is a different analogue without a comparable human safety programme.
Is IGF-1 LR3 authorised in the UK?
No UK-authorised IGF-1 LR3 medicine was identified. Authorised products containing recombinant human IGF-1 should not be treated as equivalent to LR3.
Is IGF-1 LR3 prohibited in sport?
Yes. WADA prohibits IGF-1 and its analogues at all times, and its research resources name LONG R3 IGF-1 in detection work.
Why does the longer action matter?
Longer action changes exposure, not proof of benefit. Without human safety studies, it also raises uncertainty about the duration of unwanted metabolic or growth-factor effects.
Editorial experience
From our work: how we checked this page
For topical-map item O-008, IGF-1 LR3: claims, risk, and sport status was checked as a distinct editorial task, not treated as a generic peptide page. We reviewed 6 unique external sources and 9 internal destinations in the page, then checked that the opening answer, headings, source descriptions and linked next steps stayed within the same claim boundary. The count records links in the published page and is not a claim that every source carries equal evidential weight.
Eleni Kiromitis checked study design, biomedical evidence, evidence directness and laboratory context. Dr Stavroula Nikitopoulou checked clinical claims, adverse effects, contraindications, red flags and patient-facing safety wording. Each reviewer stayed within the remit published on the governance page. Yianni Kiromitis retained responsibility for source verification, editorial decisions and correction management.
We did not use patient experience, a personal treatment outcome, seller testimony or an assumed product identity to support this page. The publication did not independently test a vial for this review. Where a page refers to a laboratory result, that result applies only to the named sample, method and attribute. We kept uncertainty beside the conclusion, recorded which source supports each material claim, and checked that the visible review date matches the publication record. A new controlled study, regulator update, corrected source, analytical report or credible safety signal can trigger reassessment through the public correction route.