Pepdexpepdex
Stack
№ 025

IGF-1 LR3

Used to drive muscle growth. A long-acting form of insulin-like growth factor 1, with limited human safety data and a real side effect profile, handle with discipline.

GH-axis
Evidence: Anecdotal

IGF-1 LR3: Used to drive muscle growth. A long-acting form of insulin-like growth factor 1, with limited human safety data and a real side effect profile, handle with discipline. IGF-1 LR3 is a long-acting form of insulin-like growth factor 1.

FDA ⓘ
Not approved
WADA
Banned
Typical dose
30-60 mcg sub-q daily
Half-life ⓘ
~20-30 hours
Route ⓘ
Subcutaneous
Schedule
Daily
In plain English

IGF-1 LR3 is a long-acting form of insulin-like growth factor 1. Used for muscle anabolism, but human safety data is thin and the side effect profile (low blood sugar, organ growth concerns) is real. Treat carefully, short cycles only.

Status & legalityWhat do these mean? →
Natty? ⓘ
Not natty

Long-acting IGF-1 analog. Universally banned in tested sport.

FDA ⓘ
Not approved

Mecasermin (Increlex) approved 2005 for severe primary IGF-1 deficiency. IGF-1 LR3 specifically (research analog) is NOT FDA approved.

Compounding ⓘ
Not classified

Not on FDA's 503A bulks list and not in any current nomination category, so it does not qualify for compounding from bulk through the bulks-list route. FDA stopped sorting new nominations into those categories in January 2025, so an absent category is not itself a finding either way.

WADA ⓘ
Banned (S2)
Prescribed ⓘ

Increlex prescribed by pediatric endocrinology for IGF-1 deficiency. IGF-1 LR3 is not prescribed.

Who it's for

  • →Experienced users who already have GH-axis baseline
  • →Short, focused anabolism cycles

What to expect

  1. Week 1

    Pumps and fullness in trained muscle. Mild hypoglycemia risk.

  2. Week 4

    Nutrient partitioning shifts noticeably. Plateau approaching by week 4.

  3. Week 8

    Cycle endpoint already passed. Cycle off well before this point.

Looking at IGF-1 LR3? Your next 3 steps

  1. 1Work out your syringe units

    Vial size + BAC water turns into the exact units to draw for IGF-1 LR3.

    Open calculator →
  2. 2See what to stack & monitor

    The companion supplements and the bloodwork worth tracking on this kind of protocol.

    Bloodwork guide →
  3. 3Save it & ask the Coach

    A free account gets you Coach questions every day, free; membership saves your stack and makes the Coach stack-aware.

    Create free account →

How it works (mechanism)

Long Arg3 IGF-1, a modified IGF-1 with arginine at position 3 and an N-terminal extension. Resists binding to IGFBPs (which normally sequester IGF-1), giving it ~3x longer half-life and stronger systemic activity than native IGF-1.

Dosing protocol

Members only

Stacks well with

Members only

Side effects

01Hypoglycemia (low blood sugar), eat carbs near dose
02Localized growth at injection site
03Theoretical: visceral organ growth at chronic high doses
04Headache

When NOT to use

  • ⚠Active malignancy (real concern with IGF-1)
  • ⚠Diabetic retinopathy
  • ⚠Pregnancy / nursing
  • ⚠Hypoglycemia-prone

Bloodwork to monitor

  • • Fasting glucose every 2 weeks
  • • IGF-1 baseline + at week 4

Common mistakes

  • • Running it longer than 4 weeks
  • • Dosing fasted (hypoglycemia)
  • • Stacking with insulin or insulin-sensitizers without monitoring

What it actually is

IGF-1 LR3 is a modified version of insulin-like growth factor 1, the hormone that carries out most of growth hormone's actual work. The modifications stop it binding the carrier proteins that normally hold IGF-1 inactive in the blood, so far more of it is free and it lasts far longer. That is the entire design: more active hormone, for longer. It has never been approved, it is banned in sport, and among the compounds in this catalog it has one of the thinnest human evidence bases and one of the more serious theoretical risk profiles.

Normally about 99% of circulating IGF-1 is bound to binding proteins, which act as both a reservoir and a brake. The LR3 modification — an arginine substitution plus a 13-amino-acid extension — greatly reduces that binding, so the hormone stays free and active with a half-life of roughly a day instead of minutes. Free IGF-1 drives cell growth and division, and it also acts on the insulin receptor, which is where the hypoglycaemia comes from: at high enough concentrations it does some of insulin's job.

Forms, and which is which

Lyophilised powder, subcutaneousHow all use happens

Reconstituted by the buyer. Research-chemical supply with no identity or potency assurance, and potency matters more here than for most peptides because the safety margin is smaller.

Verdict: The only form, and the dose accuracy problem is a safety problem.

IGF-1 DESLocal, short-acting effect

A different truncated analog with a much shorter half-life, marketed for localised action. Same absence of human evidence.

Verdict: A different unknown, not a safer one.

Recombinant IGF-1 (mecasermin)The approved comparison

Approved as Increlex for severe primary IGF-1 deficiency in children. Carries hypoglycaemia warnings and requires dosing with food — which tells you what the risk actually is.

Verdict: The regulated version, and its label is the honest guide to the risks.

Blends with growth hormone or insulinNothing

Stacks three hypoglycaemia risks. This is the combination behind the serious adverse events reported in bodybuilding contexts.

Verdict: The most dangerous configuration in this catalog.

What it is claimed to do, graded

Builds muscle in humansNone shown

The reason it is taken, and there is no human trial. The evidence index returns zero randomised trials and zero human trials for this molecule.

Promotes localised tissue growth at the injection siteNone shown

Widely believed and untested in humans. Animal work on the LR3 form is mixed: a 2025 study in growth-restricted fetal sheep found it did not promote growth.

Speeds recovery from trainingNone shown

No controlled human data.

Is safe at commonly used dosesNone shown

Hypoglycaemia is the immediate hazard and is dose-dependent. The longer-term concern is that IGF-1 signalling is directly implicated in tumour growth, and nobody has studied what supraphysiological free IGF-1 does over time in healthy adults.

Grades describe how much human evidence exists for that specific claim, not whether it will work for you or whether it is safe.

Pros and cons

Pros
  • • The underlying biology is real — IGF-1 is genuinely the mediator of most growth hormone effects
  • • An approved recombinant IGF-1 exists, so the pharmacology and its risks are actually documented
  • • Long half-life relative to native IGF-1, so once-daily dosing is workable
Cons
  • • Zero human trials of this molecule, and grade D on the site's own evidence ladder
  • • Hypoglycaemia is a real, immediate and potentially dangerous effect, not a theoretical one
  • • IGF-1 signalling is directly implicated in tumour growth, which makes any undetected cancer a serious concern
  • • Banned in sport
  • • Dose accuracy from research-chemical supply is a safety issue here, not just a value issue
  • • Commonly stacked with growth hormone and insulin, which is where the reported serious harms come from

When to stop

  • • Any hypoglycaemic episode: shakiness, sweating, confusion, palpitations — treat it, then stop
  • • Any new lump or unexplained weight loss
  • • Vision changes, given the retinopathy contraindication
  • • Persistent headaches
  • • You cannot reliably have carbohydrate available at dosing time

Interactions

InsulinAvoid

Both lower blood glucose and IGF-1 LR3 acts on the insulin receptor directly. This combination is behind the severe hypoglycaemia events reported in this space.

Sulfonylureas and other glucose-lowering drugsAvoid

Additive hypoglycaemia with no way to predict the magnitude.

Active or suspected cancerAvoid

IGF-1 is a growth signal for a wide range of tumour types. This is the most serious contraindication on the page.

Fasted trainingCaution

Dosing without carbohydrate available is the standard route to a hypoglycaemic episode.

Growth hormoneCaution

Growth hormone raises your own IGF-1. Adding exogenous IGF-1 on top compounds both the glucose and the growth-signalling concerns.

Is this for you?

Probably worth reading further if
  • • Realistically nobody, on the current evidence — and if used at all, only by someone who understands hypoglycaemia management and has glucose to hand
Skip it if
  • • You have active cancer, or any undiagnosed lump
  • • You have diabetic retinopathy
  • • You are prone to hypoglycaemia, or use insulin
  • • You are pregnant or nursing
  • • You are drug-tested in sport
  • • You are planning to stack it with growth hormone or insulin — that is the configuration that has hurt people

The one number

0 randomised trials and 0 indexed human-trial records; graded D on the Pepdex evidence ladder
Pepdex evidence index — counts are indexed PubMed records, not deduplicated trials; PubMed query for IGF-1 LR3

Sources for the claims above

Drug & supplement interactions

  • ⚠Insulin: severe hypoglycemia risk, eat carbs near dose
  • ⚠Glucocorticoids antagonize IGF-1 effects
  • ⚠Cytotoxic chemotherapy: avoid (theoretical malignancy concern)

Community patterns

Members only
Free, no account needed

New to IGF-1 LR3? Grab the starter checklist.

Drop your email and we'll send the one-page starter checklist beginners actually need first. No account needed.

No spam, and we never sell your email. Just the checklist. Email support@pepdex.co to opt out any time.

AI Coach, live sample
Member answer
is 250mcg of bpc enough for a knee injury?
For a knee, is the standard working dose and a solid place to start. The trick with BPC is consistency, give it weeks, not days. , run it , and don't drop below , results tend to fall off under that line. If nothing's moved by week 3, that's when earns its place.
how much bac water for a 10mg reta vial?
is the standard play for a 10 mg reta vial. That gives you , clean unit math across the whole titration: on a 100-unit insulin syringe. Run instead if you want fewer, more concentrated shots. Most people titrate up over , and that mix keeps the numbers cleanest.
what should i track on bloodwork for tirzepatide?
Lipid panel, ALT/AST (liver enzymes), and an A1C, baseline before you start then every 3 months. If you've got metabolic-syndrome history, add fasting glucose and insulin so you can actually watch insulin sensitivity improve. You don't need a big hormone panel for a GLP-1.

Numbers redacted in this preview. Members get the full answer, on their own stack.

Ask the Coach anything about IGF-1 LR3 or your own stack. This is it working.

Trained only on Pepdex content. Does the dose math, flags interactions, knows your stack. Won't push vendors, won't pretend to be a doctor.

Unlock the full Coach, from $4.99/week →

Frequently asked

What is IGF-1 LR3?+
IGF-1 LR3 is a long-acting form of insulin-like growth factor 1. Used for muscle anabolism, but human safety data is thin and the side effect profile (low blood sugar, organ growth concerns) is real. Treat carefully, short cycles only.
Is IGF-1 LR3 FDA approved?+
Mecasermin (Increlex) approved 2005 for severe primary IGF-1 deficiency. IGF-1 LR3 specifically (research analog) is NOT FDA approved.
Is IGF-1 LR3 legal?+
IGF-1 LR3 is not FDA-approved, so there is no approved prescription version. Most supply is sold as "research only" by peptide vendors. A compounding pharmacy may only use substances the FDA permits for compounding, and many research peptides are not permitted — do not assume a compounded prescription is available. Possession is generally not criminalized but distribution without authorization may be. Verify local laws.
Is IGF-1 LR3 banned by WADA?+
IGF-1 LR3 is on the WADA prohibited list under Banned (S2).
Are you still natty after taking IGF-1 LR3?+
No. Long-acting IGF-1 analog. Universally banned in tested sport.
Do doctors prescribe IGF-1 LR3?+
Increlex prescribed by pediatric endocrinology for IGF-1 deficiency. IGF-1 LR3 is not prescribed.
What's the typical dose of IGF-1 LR3?+
Dosing depends on your goal, experience, and tolerance. The full IGF-1 LR3 protocol (dose, frequency, and how to titrate) is in the members section on the entry page.
What are the side effects of IGF-1 LR3?+
Common side effects include: Hypoglycemia (low blood sugar), eat carbs near dose; Localized growth at injection site; Theoretical: visceral organ growth at chronic high doses; Headache. Less common effects and full safety details are on the entry page.
How long until IGF-1 LR3 starts working?+
Pumps and fullness in trained muscle. Mild hypoglycemia risk.
What can you stack with IGF-1 LR3?+
IGF-1 LR3 is commonly combined with complementary compounds. The full stacking protocol (what to pair, dosing, and timing) is in the members section on the entry page.
Where do people get IGF-1 LR3?+
Pepdex does not sell, ship, or recommend suppliers. IGF-1 LR3 is not FDA-approved; prescription versions require licensed clinical care, and "research only" markets carry real legal and quality risks. /coa explains how to verify a Certificate of Analysis and /guides/scam-vendor-spotting covers the red flags.
IGF-1 LR3 vs IGF-1 DES, which is better?+
IGF-1 LR3 vs IGF-1 DES: long-acting systemic vs short-acting local IGF-1 variants. Side effect profiles differ. Full head-to-head comparison: https://pepdex.co/compare/igf-1-lr3-vs-igf-1-des

Common questions about IGF-1 LR3

Head-to-head with IGF-1 LR3

Compare
IGF-1 LR3 vs IGF-1 DES →

Tracked alongside IGF-1 LR3

Same goal, different aisle — each graded on its own evidence in the Pepdex catalog.

MK-677 →
the oral secretagogue these peptides get compared to constantly
Creatine →
the strongest-evidence performance supplement in the catalog
Glycine →
sleep quality drives GH pulses; this is the benign first option
Melatonin →
same reason — the sleep window is the GH window

More in GH-axis

№ 022
HGH (Somatropin)

Recombinant human growth hormone, the protein itself, not a peptide that nudges your body to make more. Highest legal-risk compound in this catalog.

№ 012
MK-677 (Ibutamoren)

Oral ghrelin mimetic. Bumps GH and IGF-1 without injections. Strong appetite stimulation is the trade-off.

№ 007
Ipamorelin

Bumps your natural growth-hormone pulses without hitting cortisol or prolactin. A selective GH secretagogue.

№ 008
CJC-1295 (no DAC)

Pairs with Ipamorelin to amplify your natural growth-hormone pulses. A GHRH analog whose 'no-DAC' version stays short-acting on purpose.