IGF-1 LR3 MGF

What they are

These two peptides sit one step downstream of the GH-axis catalog. Ipamorelin, CJC-1295, Sermorelin, and Tesamorelin tell your pituitary to release more GH, which tells your liver to make more IGF-1, which then drives the muscle/recovery/sleep benefits. IGF-1 LR3 and MGF skip the GH axis entirely — they are the IGF-1 family signal, delivered as an exogenous bolus or local injection.

That changes everything about the risk-benefit calculus. The GH-secretagogues raise IGF-1 through your own physiology — pulsatile, feedback-regulated, dimmed by somatostatin when levels rise. IGF-1 LR3 is a non-physiologic bolus: by design it evades the IGF-binding proteins (IGFBPs) that normally sequester ~99% of circulating IGF-1, so a much larger fraction stays free and active. MGF is more like the body’s own local response to mechanical loading — but injected exogenously, into muscles you’ve trained, on top of whatever the natural response is.

These are not casual peptides. They have the strongest growth signal in the wiki, and they have the most explicit cancer-epidemiology concern.

How they work

The shared upstream — the IGF-1 axis

IGF-1 binds the IGF-1 receptor (IGF-1R) on muscle (and most other) cells. The receptor activates two signaling arms:

• PI3K → Akt → mTOR — protein synthesis, the hypertrophy signal.
• MAPK / ERK — cell proliferation and survival, the satellite-cell-activation signal.

In the body, almost all circulating IGF-1 is bound to IGFBPs (IGF-binding proteins) — only a small free fraction actually signals at any moment. That binding system is the natural brake on IGF-1’s potency. Native IGF-1 also has a short effective half-life (12–15 hours nominally, but the free fraction turns over in minutes).

IGF-1 LR3 — engineered to escape the brake

IGF-1 LR3 (“Long R3 IGF-1”) is an 83-amino-acid synthetic analog of native IGF-1 (70 aa). Two engineering changes give it its character:

• Arginine substitution at position 3 (the “R3”). Reduces affinity for IGFBPs by >100×.
• 13-amino-acid N-terminal extension (the “Long”). Further reduces IGFBP affinity and extends circulating half-life.

The result: most LR3 stays free in circulation rather than getting sequestered by binding proteins. That free-fraction multiplier is what produces the often-cited “2–3× the potency of native IGF-1.” Functional half-life is 20–30 hours — verified against the Francis et al. 1992 original characterization — long enough for once-daily dosing.

Honest contradiction surfaced: and worth understanding. A 2026 fitness-YouTube video (Humiston, ) confidently asserts LR3’s half-life is “10–30 minutes” on the first-principles argument that removing IGFBP binding removes the half-life-extending mechanism. That reasoning is intuitive but empirically wrong. Francis 1992 and the downstream literature confirm LR3’s plasma half-life is 20–30 hours, because the 13-aa N-terminal extension itself directly slows renal clearance and proteolytic degradation — a half-life-extending mechanism that runs parallel to the IGFBP-binding mechanism, not through it. The 1000-fold IGFBP-affinity reduction is real and confirmed (Francis 1992); the half-life consequence flows the opposite direction Humiston reasons. Surfaced here because his protocol recommendation (pre/post-workout bilateral dosing with rationale tied to a 10-30-min half-life) propagates online and OHM readers should know why the once-daily clinical default is the correct protocol — the pharmacology supports it. Use this as a worked example of why mechanism-arguments need empirical verification, not just first-principles reasoning.

Originally designed by Francis (1993) and Tomas (1996) as a research tool for IGF-1R signaling studies in cell culture. Therapeutic muscle-growth use is off-label repurposing, not the molecule’s design intent. The closest FDA-approved analog is mecasermin (rhIGF-1, Increlex) — but mecasermin is native IGF-1 and is pharmacologically not equivalent to LR3 (mecasermin gets bound by IGFBPs; LR3 doesn’t). The mecasermin clinical data informs the IGF-1-axis safety story but does not transfer cleanly to LR3 dosing.

MGF — your own muscle’s repair splice variant

MGF is the 24-amino-acid C-terminal peptide that arises from alternative splicing of your own IGF-1 gene under mechanical stress. When you lift heavy or damage muscle, the IGF-1 gene gets spliced into the IGF-1Ec isoform locally in the trained muscle — and the C-terminal piece of that splice variant is MGF. The “mechano” prefix captures the trigger: mechanical loading.

Mechanism — the satellite-cell activation half of the IGF-1 axis:

• Muscle stem cells (“satellite cells”) sit dormant in G0 between the sarcolemma and basal lamina.
• Mechanical damage → MGF release → satellite cells driven into the cell cycle.
• The MGF E-peptide promotes proliferation without premature differentiation — preserving the stem-cell pool and giving you more satellite cells per damage event.
• Satellite cells then fuse with damaged fibers → repair and add new myonuclei (hyperplasia, not just hypertrophy of existing fibers).
• Mature IGF-1 expression rises later in the natural sequence → sustained protein synthesis (hypertrophy).

That’s the natural post-workout sequence. MGF goes first, then mature IGF-1. Exogenous MGF amplifies the satellite-cell wake-up step; exogenous IGF-1 LR3 amplifies the sustained-growth step. The two are not redundant: they’re sequential.

Discovery story worth knowing. The Goldspink group at the Royal Free Hospital in London (Geoffrey Goldspink with Yang, Hill, and colleagues) identified the IGF-1Ec splice variant in stretched and damaged muscle across the late 1990s–2000s. The shift in framing — from “IGF-1 is just IGF-1” to “IGF-1 has a mechano-responsive splice variant that activates stem cells” — is one of the more genuinely interesting biology stories in the muscle-peptide world.

PEG-MGF vs standard MGF. Standard MGF has a half-life measured in minutes in circulation: practically unusable for systemic dosing. PEGylation (polyethylene glycol attached to the molecule) extends half-life to hours to days by slowing renal clearance and proteolytic degradation. Almost all research-peptide MGF use is PEG-MGF for this reason. Non-PEGylated MGF is only useful as an immediate-post-workout local injection.

What the research shows

IGF-1 LR3

Zero controlled human clinical trials for IGF-1 LR3 specifically. The dosing protocols people run derive from in vitro work, animal models, community experience, and rough analogy to mecasermin (Increlex) clinical data. That analogy is imperfect — mecasermin = native IGF-1, which behaves differently because IGFBPs sequester it.

Named primary citations under the LR3 story:

• Francis GL et al. 1993 Adv Exp Med Biol 343:113–123 — original characterization of IGF-1 analogs with reduced IGFBP affinity.
• Tomas FM et al. 1996 J Endocrinol 150(1):77–84 8708565 — “Superior potency of infused IGF-I analogs which bind poorly to IGF-binding proteins.”
• Clark R et al. 2004 Horm Res 62 Suppl 1:93–100 15761240 — rhIGF-1 risks/benefits review.
• Clemmons DR 2012 Endocrinol Metab Clin North Am 41(2):425–443 22682639 — metabolic actions of IGF-I (the hypoglycemia mechanism anchor).

The cancer epidemiology: the key safety story. Two anchor references:

• LeRoith D, Roberts CT 2003 Cancer Lett 195(2):127–137 12767520 — IGF system and cancer.
• Pollak M 2008 Nat Rev Cancer 8(12):915–928 19029956 — insulin/IGF signalling in neoplasia.

Across multiple large epidemiological studies, elevated circulating IGF-1 is associated with increased risk of prostate, breast, and colorectal cancer. The mechanism is mainstream oncology: IGF-1 is a potent mitogen (drives cell proliferation) and an apoptosis inhibitor (blocks programmed cell death): exactly the combination tumors exploit. IGF-1 LR3’s 2–3× potency over native IGF-1 amplifies the same concern. This is not theoretical risk; it’s mechanistically well-established and epidemiologically supported. Whether short-cycle exogenous use translates that population-level epi signal into actual individual risk is unknown, but the direction of concern is real.

The honest U-shape: the part most peptide content misses. The IGF-1 / mortality relationship is NOT monotonic (“more is worse”) — it is a U-shaped curve, with both very HIGH and very LOW IGF-1 associated with elevated cancer and all-cause mortality risk. Anchor citations:

• Burgers AMG et al. 2011 JCEM 96(9):2912-2920 23015658 — “Both low and high serum IGF-I levels associate with cancer mortality in older men” — quintile-1 (lowest IGF-1) hazard ratio 1.86 for cancer mortality; quintile-5 (highest) HR 1.90. The curve isn’t a slope; it’s a bathtub.
• EPIC-Heidelberg (Schöttker et al. 2023) JCEM 108(10):e1092-e1102 — restricted-cubic-splines analysis showing U-shaped IGF-1 vs cancer / cardiovascular / all-cause mortality across the general adult cohort.
• Antagonistic-pleiotropy review PMC8441393 — the dual-edge biology framing (IGF-1 supports tissue maintenance + apoptosis suppression at the same time, which produces opposite effects at population level depending on age and baseline).

The cleanest external framing comes from Dr. Kristi Sawicki (PhD molecular oncology, ): “It’s a U-shaped curve. We don’t want low IGF-1 and we don’t want high. We want to be right in the middle of that curve.”

Operational consequence for OHM readers:

1. Test IGF-1 before starting any GH-axis cycle, and re-test periodically during. The lab is cheap and the U-curve makes the data actionable. A reader who is mid-range or high should not be running a secretagogue stack to push higher; a reader who is low has a legitimate physiologic-restoration case.
2. The GHRH+GHRP secretagogue stacks (CJC-1295 / Ipamorelin, Sermorelin, Tesamorelin) are physiologic-restoration tools — their pulsatile mechanism + intact feedback loops mean they move users from the low side of the curve toward the middle, not from the middle to the high side. That is what makes the secretagogue argument rigorous.
3. Direct IGF-1 LR3 bypasses this feedback architecture entirely — it pushes IGF-1 receptor activation regardless of where circulating IGF-1 sits. That is why the LR3-specific cancer-epi concern is sharper than the secretagogue-stack concern, and why LR3 belongs in a fundamentally different risk tier.

MGF

The strongest evidence layer of any non-launch-15 muscle peptide in this wiki, on the mechanism side — but no human RCTs.

Mechanism anchors:

Study focus	First author / year
IGF-I splicing + muscle adaptation	Goldspink	16024511
MGF vs IGF-I in myoblast proliferation	Yang SY	12095637
Satellite cell activation after damage	Hill M	12692175
MGF in ALS / dystrophic muscle	Ates K	17531227
MGF in brain ischemia neuroprotection	Dluzniewska J	16144956
E-domain MGF neuronal survival	Quesada A	19735655
MGF-E in myogenic precursor pools	Kandalla PK
MGF post-MI cardiac	Mills P

Beyond muscle: MGF’s E-domain has demonstrated neuroprotective effects against brain ischemia (Dluzniewska 2005), neuronal survival support (Quesada 2009), post-myocardial-infarction cardiac repair signals (Mills), and therapeutic potential in ALS / dystrophic muscle (Ates 2007). That cross-tissue mechanism breadth is real and adds to the case that MGF is a fundamental tissue-repair signaling molecule — not just a bodybuilding peptide.

PEG-MGF half-life — the central pharmacology that makes it usable in protocols outside the immediate-post-workout local-injection scenario.

Where the science honestly stands

Both peptides have strong mechanism evidence and no controlled human clinical trials in the off-label muscle-growth use case. IGF-1 LR3 has an anchored cancer-epidemiology safety concern. MGF has a thinner safety surface but shares the IGF-1-axis class risks at theoretical level. Anyone considering these should hold both facts at the same time.

Real-world protocol

The doses and schedules here are for educational and informational purposes only. These peptides are sold for research use only and are not FDA-approved drugs. This is not medical advice. Consult a qualified physician before beginning any protocol.

IGF-1 LR3

Reconstitution math. A 1 mg (1,000 mcg) vial reconstituted with 1 mL bacteriostatic water gives 1,000 mcg/mL. On a U-100 insulin syringe:

• 20 mcg dose = 0.02 mL = 2 units
• 40 mcg dose = 0.04 mL = 4 units
• 60 mcg dose = 0.06 mL = 6 units
• 100 mcg dose = 0.10 mL = 10 units

Dosing tiers:

Tier	Dose	Notes
Beginner	20–40 mcg/day	Assess hypoglycemia tolerance; 3–5 days minimum before escalating
Intermediate	40–60 mcg/day	Weekly fasting-glucose monitoring
Advanced	60–100 mcg/day	Significant hypoglycemia + organ-growth risk; strict glucose monitoring

🚨 Mandatory hypoglycemia management. 30–50 grams of fast-acting carbs within 30 minutes of EVERY injection. Fruit juice, glucose tablets, white bread, rice: anything that hits blood glucose fast. This is not optional. Severe hypoglycemia → seizures, loss of consciousness, coma, and death have all been documented in unsupervised IGF-1 LR3 use. The rule that protects you is simple: never inject without a fast-carb plan immediately at hand.

Timing rules: these are also non-negotiable for safety:

• NEVER inject before sleep. You can’t eat while unconscious if hypoglycemia hits in the night.
• NEVER inject while fasted.
• Always inject when awake and able to eat immediately.
• Best practical timing: post-workout with a real meal.

Route: SubQ or IM. IM into the trained muscle is sometimes used for localized effect; SubQ is more common for systemic dosing.

Cycle: 4–6 weeks on, 4 weeks minimum off: non-negotiable. The rationale stacks: insulin-sensitivity recovery, organ-growth-exposure limitation, IGF-1R resensitization, and mitigation of sustained mitogenic stimulus from the cancer-epi standpoint.

Cold-chain matters. Lyophilized peptides are NOT immune to heat-degradation — denaturation and oxidation accelerate at high temperature even in the dry powder form. The Arizona-summer-mailbox failure case Humiston describes (LR3 from research-grade vendors with no temperature-controlled shipping = “absolutely nothing” effect, vs. compounded LR3 shipped with cold packs = “amazing” effect) is a real risk in any peptide shipped in hot months without an ice chest… Prefer vendors that ship with cold packs OR vendors with US fulfillment that ships ≤2 days OR order in cooler months. Once reconstituted, refrigerate.

Customer-education tell: the “receptor-tested version” marketing claim. Some research-grade vendors advertise an LR3 “receptor version” or “receptor-tested batch” as a premium tier — claiming they’ve tested the IGF-1R binding affinity of the batch and segregated the “best” molecules. Chemistry says that’s nonsense: testing IGF-1R binding affinity is expensive, slow, and ratings-based — you can’t filter out the bad stuff at the binding-affinity level; you have to downgrade the entire batch. It’s marketing language for “purity,” not a real chemistry process… Treat the phrase as a tell that the vendor is marketing-coding rather than chemistry-coding.

MGF (PEG-MGF)

Reconstitution math. A 2 mg (2,000 mcg) vial reconstituted with 2 mL bacteriostatic water gives 1,000 mcg/mL. On a U-100 insulin syringe:

• 200 mcg dose = 0.20 mL = 20 units
• 300 mcg dose = 0.30 mL = 30 units
• 400 mcg dose = 0.40 mL = 40 units

Dosing tiers (PEG-MGF):

Tier	Per-injection dose	Frequency	Weekly total
Beginner	200 mcg	2×/week	400 mcg
Intermediate	300 mcg	2–3×/week	600–900 mcg
Advanced	400 mcg	3×/week	1,200 mcg

Standard (non-PEG) MGF: 100–200 mcg IM immediately post-workout into the trained muscle (within minutes — the minute-range half-life forces tight timing).

Critical timing rules:

• Inject on TRAINING DAYS ONLY, into TRAINED muscle. MGF amplifies the satellite-cell activation triggered by mechanical damage. No damage = no substrate = no effect. The “magic injection” framing misses the entire mechanism.
• PEG-MGF: within 1–2 hours post-workout.
• Standard MGF: within minutes post-workout.
• IM preferred over SubQ for localized satellite-cell activation in the target muscle.
• Site rotation mandatory to avoid local tissue damage / scarring.

Cycle: 4–6 weeks on / 4–6 weeks off. Periodization-aligned use is the smart frame — load during high-volume hypertrophy blocks; cycle off during strength / deload phases.

Stacking — the sequence

The advanced muscle-peptide stack runs MGF first, IGF-1 LR3 second — matching the natural post-workout sequence (satellite-cell activation, then sustained growth). In practice that means:

• MGF dosed at the workout window (PEG-MGF 1–2 hr post; standard MGF immediately post).
• IGF-1 LR3 dosed at a separate window — post-workout meal time (the carb requirement coincides naturally).
• Cross-cycle stack with CJC-1295 / Ipamorelin for the GH-axis baseline lift.
• Some users run Follistatin 344 in parallel for the myostatin-brake-removal layer (mechanism stacking across all three muscle-growth levers: GH/IGF-1 axis up, IGF-1 axis directly up, myostatin brake down). The safety profile of a triple-stack like this is unstudied.

Side effects & management

IGF-1 LR3

Effect	Severity / mechanism	Management
Severe hypoglycemia	Life-threatening — seizures, coma, death documented	30–50 g fast-acting carbs within 30 min of every injection; never dose pre-sleep / fasted
Visceral organ hypertrophy	“Palumboism” / abdominal distension; cardiac hypertrophy	Cycle limits (4–6 wk max on); dose ceilings
Insulin resistance / fasting glucose rise	Progressive on chronic use	Monitor fasting glucose + HbA1c every cycle
Joint pain / swelling	Common at higher doses	Dose adjustment
Headache, lethargy, numbness/tingling, injection-site reactions	Manageable	Standard cycle hygiene
Cancer-pathway stimulation	IGF-1 axis cancer epi (prostate / breast / colorectal)	Avoid with any active cancer or strong cancer-history risk profile

Absolute contraindications for IGF-1 LR3:

1. Active cancer or cancer history
2. Strong family history of cancer in IGF-1-sensitive cancer types (prostate, breast, colorectal)
3. Diabetes (Type 1 or Type 2)
4. Significant cardiac conditions
5. Pregnancy and breastfeeding
6. Under 25 (still-developing physiology)
7. Concurrent insulin use
8. Active organ disease (liver/kidney)

MGF (PEG-MGF)

Lighter overall safety surface than LR3:

• Injection-site pain / swelling (24–48 hr resolution).
• Localized muscle soreness.
• Mild hypoglycemia (dizziness, shakiness, sweating) — much less severe than LR3.
• Transient tissue swelling.

Theoretical concerns:

• Chronic satellite-cell stimulation — satellite cells are stem-like; sustained activation could in principle drive aberrant tissue overgrowth.
• Localized tissue overgrowth with repeated same-site injection (rotate sites).
• Shared IGF-1 family risks at theoretical level: insulin-sensitivity changes, theoretical tumor-promotion.

Contraindications:

• Active cancer or cancer history.
• Pregnancy / breastfeeding.
• Uncontrolled diabetes.
• Active infection at injection site.
• Autoimmune muscle conditions (dermatomyositis, polymyositis).

Regulatory status

Both peptides: not FDA-approved for any indication; research-chemical classification; WADA-prohibited at all times. Mecasermin (Increlex) is the FDA-approved rhIGF-1 product, indicated for severe primary IGF-1 deficiency in pediatric patients — it is not IGF-1 LR3 and the labeling doesn’t transfer. No approved indication for MGF or PEG-MGF.

Technical & analytical reference (chemistry & QC)

Verified identity values (identity confirmed below; do NOT pull identity from the analytical capture — the source has errors). The capture’s MGF MW of 2948.15 is wrong; use ~2867.

Peptide	Formula	Avg MW	CAS	Sequence	PubChem CID
MGF (IGF-1Ec)	C121H200N42O39	~2867	none established	IGF-1Ec C-terminal 24-mer	none by name
PEG-MGF	MGF + PEG (variable MW)	variable (MGF core + PEG)	none established	PEGylated MGF	—

Notable analytical / QC detail (per peptide):

• MGF — the PeptideBiologix capture lists MW 2948.15; this is incorrect. The IGF-1Ec C-terminal 24-mer average MW is ~2867 (corrected here). There is no PubChem record indexed under the “MGF” name.
• PEG-MGF — the raw capture is internally inconsistent about whether the product is full-length MGF or a shorter 13-mer fragment; treat the exact peptide length as uncertain pending confirmation, and note PEG mass is variable, so a single fixed MW for PEG-MGF should not be quoted.

Citation leads (PeptideBiologix; until confirmed): PeptideBiologix analytical pages for MGF and PEG-MGF (raw captures, peg-mgf.md) — method/PK detail only; identity values above are corrected/verified, not taken from the captures.

Sources

1. Research note — IGF-1 LR3 + MGF muscle cluster (text aggregation: structure, mechanism, dosing, safety, named primary PMIDs).
2. Tomas FM, et al. Superior potency of infused IGF-I analogs which bind poorly to IGF-binding proteins. J Endocrinol 1996. 8708565
3. Clark R et al. rhIGF-1 risks and benefits review. Horm Res 2004. 15761240
4. Clemmons DR. Metabolic actions of IGF-I. Endocrinol Metab Clin North Am 2012. 22682639
5. LeRoith D, Roberts CT. The insulin-like growth factor system and cancer. Cancer Lett 2003. 12767520
6. Pollak M. Insulin and insulin-like growth factor signalling in neoplasia. Nat Rev Cancer 2008. 19029956
7. Goldspink G. IGF-I splicing and muscle adaptation. 16024511
8. Yang SY. MGF vs IGF-I in myoblast proliferation. 12095637
9. Hill M. Satellite cell activation after muscle damage. 12692175
10. Dluzniewska J. MGF E-domain neuroprotection in brain ischemia. 16144956
11. Quesada A. E-domain MGF neuronal survival. 19735655
12. Ates K. MGF in ALS / dystrophic muscle. 17531227
13. peptidewiki.co — IGF-1 LR3 dosage guide. https://peptidewiki.co/guides/dosage-guides/igf-1-lr3-dosage-guide
14. peptidewiki.co — MGF dosage guide. https://peptidewiki.co/guides/dosage-guides/mgf-dosage-guide
15. Frontiers Endocrinology — MGF review. https://www.frontiersin.org/journals/endocrinology/articles/10.3389/fendo.2012.00131/full

See also: Ipamorelin, CJC-1295, CJC-1295 / Ipamorelin, Sermorelin, Tesamorelin, MK-677 (Ibutamoren), GHRP-2, GHRP-6, and Hexarelin — the injectable ghrelin-receptor GH peptides, Follistatin 344, BPC-157, TB-500.