# IGF-1 LR3

Long-acting IGF-1 analogue (a cell-culture reagent) for muscle; hypoglycaemia, tumour-growth signal.

- Page: https://peprank.xyz/peptides/igf-1-lr3
- Category: Hormones & libido (Research peptide)
- Also known as: Long R3 IGF-1; LR3IGF-I / Long Arg3 IGF-I; 'IGF', 'LR3', 'IGF-1 LR3'
- Routes: Injection
- Safety tier: Strict: Avoid · Balanced: Avoid · Evidence only: Caution
- Risk axes (0 none to 3 severe): Seen harm 1, Mechanism 3, Data gap 3, Silent harm 3, Product 3
- Positive: 40% of 24 graded reports glowing or positive, shrunk toward the 49% all-report average by 8 reports' weight
- Rank: #54 of 61 research peptides
- Graded reports: 24 (Glowing 2, Positive 7, Mixed 5, Nothing 5, Negative 4, Bad reaction 1)
- Evidence: Animal only — No human study of IGF-1 LR3. It was developed around 1990 in Adelaide, is sold mainly as a cell-culture reagent, and was tested only in rats, pigs and marmosets. The closest human data come from full-length IGF-1 (mecasermin, Increlex), which is a different molecule: shorter acting and held in check by binding proteins.
- Access: Grey market
- Onset: Pumps and fullness within days; users describe strength and size changes after 2-4 weeks.
- Lasts: Half-life reported as 20-30 hours (versus minutes for native IGF-1), so one daily dose; users run 4-8 week cycles because the effect fades with tolerance.
- Cost per month: ≈ €36–140 (researchers' estimate)
- Dose users report: 27–60 mcg/day (median 30 mcg, n=7)
- Updated: 2026-10-30

**Why Avoid under the strict bar:** A potent, long-acting IGF-1 receptor agonist with no human data at all: it accelerated tumour growth in mice, the same receptor causes hypoglycaemic seizures and carries a malignancy warning on the approved IGF-1 drug, and every vial is grey-market.

## What users report

Split reports. Fans describe big pumps, fuller muscles, faster recovery and quick strength gains, often within 2-3 weeks. One user noticed less pain from a long-standing shoulder strain, and one 21-year-old says he gained weight and 2 cm of height. Most positive reports come from people also on testosterone, anavar, HGH or GLP-1s, so the effect cannot be separated out. Common downsides are water weight and puffiness, lethargy, tension headaches, intense soreness, light-headedness and hypoglycaemia symptoms when dosed without carbs; users keep dextrose or gummy bears to hand. There was one ER visit for a racing heart (normal ECG) and one report of a swollen prostate. At least one 17-year-old reports taking it, and younger teens keep asking about it. Felt nothing: About a fifth of first-hand reports felt nothing beyond a pump, and sceptics in every thread call it a waste next to growth hormone; a few blame degraded or fake vials, since it breaks down quickly once mixed..

**Effects:** big muscle pumps and fullness; faster recovery between sessions; quick strength gains (largely water in some reports); lean-mass gain, mostly reported on top of steroids

**Downsides:** hypoglycaemia (shaky, faint, 'felt like crap' when taken fasted); water retention and puffy face in the first weeks; lethargy, tension headaches; severe next-day soreness in some; tolerance after 3-4 weeks, so it is cycled; expensive for what users get

**Risks:** Strong IGF-1 receptor activation that IGF-binding proteins barely hold back: accelerated tumour growth in a mouse cachexia model; theoretical promotion of existing or undiagnosed cancers; Hypoglycaemia, potentially severe: it is 2-3 times more potent than IGF-1 at lowering glucose in animals, and the approved IGF-1 drug causes hypoglycaemic seizures; Organ and soft-tissue growth seen with IGF-1 therapy (tonsils, spleen, kidneys, facial soft tissue) and with LR3 in rat gut; Never tested in humans; a His-tagged lab reagent has been found in a black-market vial

**Caveat:** No human pharmacokinetic or dosing data exist, so every community dose is extrapolated from cell-culture potency and bodybuilding forums. Reddit sentiment is heavily confounded by steroids and GLP-1s taken at the same time, and users report that LR3 barely moves a standard IGF-1 blood test, so they cannot check that a vial is active.

**Typical use:** Community dosing is 20-100 mcg/day subQ or IM, usually after training with 0.5-1 g of fast carbs per mcg, for 4-8 weeks then the same time off. Never fasted.

**Getting it:** Research-peptide vials only; it has never been a medicine anywhere. Usually reconstituted in 0.6% acetic acid because it degrades fast in bacteriostatic water. Banned in sport by WADA (S2).

**Stacked with:** Testosterone, anavar and other steroids (Most of the strongly positive reports come from people running it on top of a steroid cycle.); HGH or CJC-1295/ipamorelin (Often run alongside to offset feedback suppression of the user's own GH; many commenters say HGH alone is cheaper and better.); Retatrutide or tirzepatide (Added during or after a GLP-1 cut to hold muscle; users on both report hypoglycaemia crashes and sugar cravings.); PEG-MGF (An old forum protocol alternates weeks of LR3 and PEG-MGF; no data supports it.)

## Risk profile

- **Seen harm 1/3:** No published case report or trial involves IGF-1 LR3 itself. On Reddit there is one ER visit for a persistent racing heart (normal labs and ECG) and repeated self-reported hypoglycaemia symptoms, all anecdotal. The mecasermin label warnings (hypoglycaemic seizures, malignancy) belong to a different molecule and are carried in mechanism and dataGap.
- **Mechanism 3/3:** LR3 is a full IGF-1 receptor agonist that IGF-binding proteins barely restrain. In tumour-bearing mice it accelerated tumour growth in vivo, which is the harm itself shown for this molecule. In pigs and marmosets it is 2-3 times more potent than IGF-1 at lowering glucose, with a longer effect, and full-length IGF-1 causes hypoglycaemic seizures in humans.
- **Data gap 3/3:** No human has been dosed with LR3 in any published study; it was characterised only in cells, rats, pigs and marmosets. Mecasermin (71 children in the label studies, 330 adults in a 2-year ALS trial) is a different molecule. LR3 has a 13-residue extension, an arginine substitution, a far longer half-life and almost no binding-protein buffering, so those data bridge only loosely.
- **Silent harm 3/3:** The serious feared harm is promotion of existing or undiagnosed tumours by sustained IGF-1 receptor signalling, which is silent and delayed and which testimonials cannot reveal. Hypoglycaemia, the acute harm, is noticed at once.
- **Product 3/3:** Bought only as grey-market lyophilised vials and injected subQ or IM. It is unstable once reconstituted (users mix it in acetic acid and complain of cloudy vials), and a black-market vial was found to contain a His-tagged laboratory form never meant for injection. Standard IGF-1 blood tests cannot confirm what is in the vial.
- **Never if:** Active or past cancer, or a strong family history or known predisposition to cancer; Pregnancy or breastfeeding (no human reproductive data); Children and teenagers with open growth plates; Diabetes, insulin or sulfonylurea use, or a history of hypoglycaemia; Use while fasting or before driving, as with the IGF-1 drug label

## Top reports

- Glowing, recovery: “So I started cycling it a little under a year ago. 6 weeks on 4-6 off. And lemme tell ya I’ve never had a more potent driver for just straight lean mass.” — [r/moreplatesmoredates](https://www.reddit.com/r/moreplatesmoredates/comments/1rykwss/igf_1_lr3_has_been_magic_for_me/)
- Glowing, recovery, 35 mcg 5x/week: “with the igf I’ve been able to gain weight and 2 cm of height because of my young bone age.” — [r/BodyHackGuide](https://www.reddit.com/r/BodyHackGuide/comments/1rp3and/1_month_progress_igf1/o9i40b0/)
- Positive, recovery, 100 mcg: “For 5 weeks now and at first I wasn’t getting much results !!! Then I altered my dose to how I was eating and what I was eating and I noticed a huge improvement.” — [r/moreplatesmoredates](https://www.reddit.com/r/moreplatesmoredates/comments/1v8lyxf/igf1lr3_how_i_got_results/)
- Positive, recovery, 40 then 60 mcg/day: “Insane pumps first couple weeks. On week 4/5 and increased dose from 40mcg to 60mcg and almost feel like I’ve gotten used to it / my receptors are less sensitive to it” — [r/BiohackingU](https://www.reddit.com/r/BiohackingU/comments/1qgr1uv/igf1_lr3_experiences/o4uddgn/)
- Positive, recovery, 40 mcg 5 days/week: “So far I noticed bigger pumps in the gym and I recover faster. I also take cjc-ipa as well. In regards to strength and growth it’s hard to say at the moment if it’s higher than naturally.” — [r/BodyHackGuide](https://www.reddit.com/r/BodyHackGuide/comments/1sa3mfa/on_the_fence_with_igf1lr3/odxlhg4/)

## Studies

- [Levolger et al. 2019: ALK4/5 inhibition attenuates cancer cachexia-associated muscle wasting (with an LR3 IGF-I arm)](https://pubmed.ncbi.nlm.nih.gov/31285507/) (animal, 2019): In tumour-bearing mice, LR3 IGF-I limited muscle loss but at the expense of accelerated tumour growth.
- [Tomas 2001: LR3IGF-I ameliorates the loss of body weight but not of skeletal muscle during food restriction](https://pubmed.ncbi.nlm.nih.gov/11472075/) (animal, 2001): A week's LR3 infusion kept body weight 3-8% higher in food-restricted rats but did not conserve muscle protein; in adult rats it increased protein breakdown and reduced protein synthesis.
- [Tomas et al. 1992: IGF-I and especially IGF-I variants are anabolic in dexamethasone-treated rats](https://pubmed.ncbi.nlm.nih.gov/1371669/) (animal, 1992): LR3 and des(1-3)IGF-I were about 2.5 times more potent than IGF-I at reversing steroid-induced weight and nitrogen loss in rats.
- [Read et al. 1992: IGF-I and its N-terminal modified analogues induce marked gut growth in dexamethasone-treated rats](https://pubmed.ncbi.nlm.nih.gov/1613443/) (animal, 1992): IGF-I raised gut weight by up to 60% in a week; LR3 and des(1-3)IGF-I did the same at severalfold lower doses, showing organ growth tracks potency.
- [Tomas et al. 1997: IGF-I variants that bind poorly to IGF-binding proteins show more potent and prolonged hypoglycaemic action in pigs and marmosets](https://pubmed.ncbi.nlm.nih.gov/9415072/) (animal, 1997): LR3 and the other variants were 2-3 times more potent than IGF-I at lowering glucose and kept it down 4-8 times longer in total.
- [Increlex (mecasermin, recombinant IGF-1) prescribing information: pooled clinical studies in primary IGF-1 deficiency](https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/021839s033lbl.pdf) (open-label, n=71, 2025): Over 3.9 years on average, 42% of children had hypoglycaemia, 4 had seizures or loss of consciousness, 15% had tonsil enlargement and kidneys and spleen grew; post-marketing malignancies led to a contraindication in cancer.
- [Jabri et al. 1994: adverse effects of recombinant human IGF-I in obese insulin-resistant type II diabetic patients](https://pubmed.ncbi.nlm.nih.gov/8314009/) (open-label, n=7, 1994): High-dose subcutaneous IGF-1 in adults had to be stopped in all seven patients for facial and hand oedema, jaw pain, joint and muscle pain, tachycardia, flushing and orthostatic hypotension.
- [Sorenson et al. 2008: subcutaneous IGF-1 is not beneficial in a 2-year ALS trial](https://pubmed.ncbi.nlm.nih.gov/19029516/) (rct, n=330, 2008): Two years of twice-daily full-length IGF-1 gave adults with ALS no benefit in muscle strength, function or survival over placebo.
- [Renehan et al. 2004: IGF-I, IGFBP-3 and cancer risk, systematic review and meta-regression](https://pubmed.ncbi.nlm.nih.gov/15110491/) (meta-analysis, n=10746, 2004): Across 21 studies, higher circulating IGF-1 was associated with prostate cancer (OR 1.49) and premenopausal breast cancer (OR 1.65).
- [Dominikowski et al. 2026: performance-enhancing peptides modulating the GH-IGF-1 axis (review)](https://pubmed.ncbi.nlm.nih.gov/42395176/) (review, 2026): Places IGF-1 LR3 and PEG-MGF in the tier with no human studies, and lists dysglycaemia, fluid retention and muscle and joint pain among reported harms of self-administered GH/IGF-axis peptides.

## Sources

- [Increlex (mecasermin) prescribing information, revised 07/2025](https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/021839s033lbl.pdf)
- [Kohler et al. 2010: detection of His-tagged Long-R3-IGF-I in a black market product](https://pubmed.ncbi.nlm.nih.gov/20675162/)
- [Thomas et al. 2017: determination of LongR3-IGF-I, R3-IGF-I and des(1-3)IGF-I in human plasma by LC-MS (anti-doping)](https://pubmed.ncbi.nlm.nih.gov/28668757/)
- [WADA Prohibited List 2026 (S2.3: IGF-1 and its analogues, including LR3IGF-1)](https://www.wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf)
- [Mendias & Awan 2026 preprint: 6441 grey-market peptide samples, 41.6-71.1% failed quality criteria, 15% endotoxin](https://europepmc.org/article/PPR/PPR1182497)