A single small clear glass vial of white lyophilized freeze-dried powder standing on a clean white laboratory bench with blurred lab glassware behind it.

IGF-1 LR3: The Complete Guide to Long R3 IGF-1 (2026)

Updated 2026-06-15T00:00:00.000Z22 min read · 5,761 words

IGF-1 LR3 is a lab-modified version of insulin-like growth factor 1, a natural muscle-and-growth hormone, engineered to stay active in the body far longer than the natural version. The single change that defines it is durability: where natural IGF-1 lasts only minutes in the bloodstream, IGF-1 LR3 has a reported half-life of roughly 20 to 30 hours. It is not an approved medicine, and it is most legitimately used not in people at all, but as a supplement that helps cells grow in pharmaceutical manufacturing.

If you have read about IGF-1 LR3 in a bodybuilding or anti-aging context, this guide is the high-level map of the whole compound: what it actually is, how the "LR3" modification works, what it is studied and used for, the dose ranges reported in research, the side effects and the real hypoglycemia risk, where it stands legally, and how people obtain it. Each section is a clear overview. For the deep-dive topics, like a full dosing chart or a side-effect management plan, we point you to dedicated guides so this page stays a clean hub, and for the wider field see our roundup of the best peptides for muscle growth.

Key Takeaways

  • IGF-1 LR3 is a synthetic, longer-lasting analog of IGF-1. It is built from 83 amino acids versus the 70 of natural IGF-1, with an arginine swapped in at position 3 and a 13-amino-acid extension on one end (ChemicalBook, 2024).
  • Its defining feature is a long half-life of about 20 to 30 hours, compared with minutes for natural IGF-1, because the modifications let it avoid the binding proteins that normally clear IGF-1 quickly (ChemicalBook, 2024).
  • It is not approved for human use anywhere. A natural-sequence IGF-1 medicine (mecasermin, brand name Increlex) is FDA-approved for a rare childhood growth disorder, but IGF-1 LR3 specifically is a research chemical, not a drug (DailyMed / FDA Increlex label).
  • Its main legitimate use is industrial, not personal. Under the trade name LONG R3 IGF-I it is widely used to boost cell growth in pharmaceutical manufacturing, where it can raise protein yield in cell culture by up to about 62% over no supplement (Repligen, "LONG R3 IGF-I").
  • The most serious physical risk is low blood sugar (hypoglycemia). Because it acts like insulin and lasts a long time, its glucose-lowering effect persists for many hours (ChemicalBook, 2024).
  • It is banned in sport at all times under WADA category S2 (growth factors) (USADA, "IGF-1 and the WADA Prohibited List").

What is IGF-1 LR3?

IGF-1 LR3 is a synthetic, longer-lasting version of insulin-like growth factor 1 (IGF-1), a natural hormone your body uses to drive cell growth and repair. The name is shorthand for "Long R3 IGF-1," which describes exactly what was changed: it is a longer molecule with an arginine (the "R3" part) substituted into the chain. It is not a drug; it is a research compound.

To understand IGF-1 LR3, start with natural IGF-1. IGF-1 is a peptide hormone, mostly made in the liver in response to growth hormone, that tells muscle, bone, and other tissues to grow and repair. Natural IGF-1 has a problem for anyone trying to use it: in the bloodstream it is grabbed almost immediately by carrier molecules called IGF-binding proteins (IGFBPs), so its free, active half-life is only a few minutes. IGF-1 LR3 is the engineered answer to that problem.

Chemically, IGF-1 LR3 is built from 83 amino acids, compared with the 70 in natural IGF-1. It has an arginine in place of a glutamic acid at the third position, and an extra 13-amino-acid extension added to one end of the chain (ChemicalBook, "Mechanism and Side Effects of IGF-1 LR3", 2024, retrieved 2026-06-15). Those two changes dramatically lower its affinity for the IGFBPs, so it slips past the carriers that would normally clear it, while still switching on the same IGF-1 receptor. If injectable peptides are new to you, our what are peptides and how peptides work guides cover the basics first.

Citation capsule. IGF-1 LR3 (Long R3 IGF-1) is a synthetic analog of human IGF-1 with 83 amino acids (versus 70 in native IGF-1): an arginine replaces the glutamic acid at position 3, and a 13-amino-acid sequence is added at the N-terminus. These changes give it very low affinity for IGF-binding proteins and a reported half-life of about 20-30 hours, versus minutes for native IGF-1. It is a research chemical, not an approved drug. Source: ChemicalBook, 2024; Repligen LONG R3 IGF-I product data.

A single small clear glass vial of white lyophilized freeze-dried powder on a clean white laboratory bench with blurred lab glassware behind it.

How does IGF-1 LR3 work?

IGF-1 LR3 works by activating the IGF-1 receptor on cells and then staying active for many hours, which signals tissues to take up nutrients, make new protein, and grow. It is the long duration, not a different mechanism, that sets it apart from natural IGF-1.

In simple terms, IGF-1 LR3 docks onto the same receptor that natural IGF-1 uses, but because it dodges the binding proteins that normally clear IGF-1, it keeps that receptor switched on far longer. When the IGF-1 receptor is activated, it triggers two main internal pathways: the PI3K/Akt pathway, which drives protein synthesis and nutrient uptake, and the MAPK/ERK pathway, which stimulates cells to divide and multiply (Peptides Explorer, "IGF-1 LR3 Dosage Protocol", 2026, retrieved 2026-06-15). The reason this matters for muscle is that IGF-1 signaling also activates satellite cells, the stem-cell-like repair cells in muscle, which is the mechanistic basis for claims about new muscle-cell formation (hyperplasia) on top of cell enlargement (hypertrophy).

The headline pharmacology is the half-life. Natural IGF-1 is active for minutes; IGF-1 LR3 is reported to remain active for roughly 20 to 30 hours (ChemicalBook, 2024, retrieved 2026-06-15). That single difference is the whole point of the molecule, and it is also the root of its biggest risk: an insulin-like, glucose-lowering effect that does not switch off quickly. The deeper receptor-signaling science lives in our how peptides work guide, so we keep it at overview level here.

A conceptual photoreal image of skeletal muscle tissue at the cellular level with glowing translucent blue and amber muscle fibers and bright signaling points representing growth-factor receptor activation.

Why does the "LR3" modification work? The Arg3 substitution explained

The "LR3" name encodes the two edits that make the molecule durable: an arginine (R) swapped in at the third position, and a "Long" 13-amino-acid extension added to the front of the chain. Together they make IGF-1 LR3 a poor fit for the IGF-binding proteins that normally trap and clear native IGF-1, so more of it stays free and receptor-available. The chemistry of those two edits is the whole reason the compound behaves differently from the natural hormone.

Start with native IGF-1's problem. In the bloodstream, almost all native IGF-1 is captured by a family of six carrier molecules called IGF-binding proteins (IGFBP-1 through IGFBP-6). While IGF-1 is held by an IGFBP it cannot reach or switch on the IGF-1 receptor, so the binding proteins act as a brake that keeps free, active hormone scarce and short-lived. The "LR3" engineering is aimed squarely at loosening that brake.

The "R3" edit is a single amino-acid substitution: an arginine replaces the glutamic acid at position 3 of the IGF-1 chain (Wikipedia, "IGF-1 LR3", 2026, retrieved 2026-06-15). Position 3 sits in the region IGF-binding proteins grip, so changing the charge and shape there disrupts the binding-protein interface. The "Long" edit adds a 13-amino-acid extension (sequence MFPAMPLLSLFVN) to the N-terminus of the molecule, taking it from 70 amino acids to 83 (Wikipedia, "IGF-1 LR3", 2026, retrieved 2026-06-15). That extra tail further hinders the binding proteins from latching on.

The combined effect is large. The two modifications give IGF-1 LR3 greater than 100-fold lower affinity for the binding proteins (IGFBP-1 through IGFBP-6) than native IGF-1 has (R&D Systems / Bio-Techne, "Recombinant Human LR3 IGF-I Protein", retrieved 2026-06-15). Crucially, the edits sit away from the part of the molecule that docks onto the IGF-1 receptor, so the analog still activates that receptor normally; it simply does so without being sequestered first. The net result is an analog reported to be roughly three times more potent than native IGF-1 in the body (Wikipedia, "IGF-1 LR3", 2026, retrieved 2026-06-15).

Citation capsule. The "LR3" in IGF-1 LR3 stands for "Long R3": an arginine substituted for glutamic acid at position 3, plus a 13-amino-acid N-terminal extension (MFPAMPLLSLFVN). These two edits cut its affinity for the six IGF-binding proteins (IGFBP-1 to -6) by more than 100-fold versus native IGF-1, leaving most of the circulating analog free to activate the IGF-1 receptor. It is reported to be about three times more potent than native IGF-1. Source: Wikipedia (2026); R&D Systems / Bio-Techne LR3 IGF-I product data.

How does reduced IGFBP binding extend its half-life?

Because IGF-1 LR3 largely escapes the binding proteins, much more of it stays free and active, which stretches its bioactive half-life from the minutes seen with native IGF-1 to a reported 20 to 30 hours. Lower binding-protein affinity and longer duration are two sides of the same coin.

The mechanism is straightforward once the binding-protein role is clear. Native IGF-1 that is captured by an IGFBP is taken out of the active pool, and free IGF-1 is cleared from circulation quickly, so its free, active window is only a few minutes. By dodging the binding proteins, IGF-1 LR3 keeps a much larger fraction of each dose in the unbound, receptor-ready state, and that free fraction persists far longer before it is cleared.

The reported figures show the scale of the difference. IGF-1 LR3 has a reported active half-life of about 20 to 30 hours, versus minutes for free native IGF-1 (Wikipedia, "IGF-1 LR3", 2026, retrieved 2026-06-15; ChemicalBook, 2024, retrieved 2026-06-15). A useful reference point is the FDA-approved native-sequence IGF-1 medicine, mecasermin (Increlex): even as a finished drug it has a mean terminal half-life of about 5.8 hours after a subcutaneous dose (DailyMed / U.S. FDA, "INCRELEX (mecasermin) injection" label, retrieved 2026-06-15). That IGF-1 LR3's reported duration runs several times longer than even an approved IGF-1 product is the entire point of the molecule, and it is exactly why its insulin-like, glucose-lowering effect lingers for so long.

Active half-life: native IGF-1 vs IGF-1 DES vs IGF-1 LR3Why "LR3" exists: it lasts far longerApproximate active half-life, shown on a log scale (each step is roughly 10x).Native IGF-1a few minutesIGF-1 DES~20-30 minutesIGF-1 LR3~20-30 hoursIllustrative, log scale. Sources: ChemicalBook (2024); Swolverine DES/LR3 comparison (2025).
The "LR3" modification trades the localized, short action of natural IGF-1 for a long systemic one, which is also why its blood-sugar effect lasts for hours.

What is IGF-1 LR3 used for?

IGF-1 LR3 has one well-established, legitimate use, and one widely discussed but unapproved one. The legitimate use is industrial: it boosts cell growth in pharmaceutical manufacturing. The unapproved use is personal: people use it off-label hoping for muscle growth, recovery, and anti-aging effects. Only the first is a recognized, lawful application.

The use most people never hear about is by far the biggest. Under the trade name LONG R3 IGF-I, IGF-1 LR3 is a standard cell-culture supplement in bioprocessing: it is added to vats of mammalian cells (such as CHO cells) that manufacture antibody drugs and other biologics, where it keeps cells alive and productive longer. In that setting it has been shown to improve protein yield by up to about 62% over no supplement and around 40% over insulin alone (Repligen, "LONG R3 IGF-I Cell Culture Supplement", retrieved 2026-06-15). This is the molecule's true home, and it is why it exists as a commercial product at all.

The use most searches are actually about is off-label and unapproved. In bodybuilding and "biohacking" circles, IGF-1 LR3 is used in the hope of:

  • Muscle growth, by driving protein synthesis and, in theory, new muscle-cell formation
  • Faster recovery from training and, anecdotally, soft-tissue injury
  • Improved nutrient partitioning, pushing glucose and amino acids into muscle
  • Anti-aging and skin claims, extrapolated from IGF-1's role in tissue repair

It is important to be honest about the evidence gap here: these personal-use claims rest largely on IGF-1's known biology, animal studies, and user reports, not on controlled human trials of IGF-1 LR3 itself. No regulator has reviewed or approved it for any of these uses (Hubmed, "IGF-1 LR3 in Aesthetic and Anti-Aging Medicine", 2025, retrieved 2026-06-15).

A photorealistic laboratory bioprocessing scene with rows of cell-culture flasks and bioreactor glassware holding faintly amber growth media on a sterile lab bench.

How is IGF-1 LR3 different from regular IGF-1, IGF-1 DES, and mecasermin?

The IGF-1 family is one molecule with several variants, and they differ mainly in how long they stay active and whether they are approved. Regular IGF-1 and mecasermin are the natural sequence; IGF-1 LR3 and IGF-1 DES are lab modifications tuned for duration. Knowing the difference prevents a lot of confusion.

Here is the practical map of the family:

VariantWhat it isActive durationStatus
Native IGF-1The natural human hormone (70 amino acids)Minutes (cleared by binding proteins)The body's own molecule
Mecasermin (Increlex)Recombinant native-sequence rhIGF-1Short; dosed as a medicineFDA-approved for severe primary IGF-1 deficiency in children
IGF-1 LR3Long modified analog (83 amino acids)~20-30 hours, systemicResearch chemical, not approved
IGF-1 DESTruncated analog~20-30 minutes, localizedResearch chemical, not approved

The most important row is mecasermin. A natural-sequence IGF-1 drug is FDA-approved: mecasermin (brand name Increlex) was approved in 2005 for the long-term treatment of growth failure in children with severe primary IGF-1 deficiency, a rare disorder (DailyMed / U.S. FDA, "INCRELEX (mecasermin) injection" label, retrieved 2026-06-15). That approval is for the natural sequence, in a narrow pediatric condition, under medical supervision. It does not cover IGF-1 LR3, and it does not make the long analog a medicine.

A quick three-way contrast makes the family clear, because the differences are mostly about sequence and duration:

  • Native IGF-1 is the body's own 70-amino-acid hormone. Free native IGF-1 is captured by IGF-binding proteins and cleared within minutes, so on its own it is impractical to dose.
  • Mecasermin (Increlex) is recombinant human IGF-1 made in E. coli with a sequence identical to native IGF-1 (70 amino acids), so it is the natural molecule manufactured as a sterile, FDA-approved injectable. Because it is the native sequence, it is still subject to the binding proteins, and its mean terminal half-life after a subcutaneous dose is about 5.8 hours (DailyMed / U.S. FDA, "INCRELEX (mecasermin) injection" label, retrieved 2026-06-15).
  • IGF-1 LR3 is the 83-amino-acid engineered analog whose Arg3 substitution and 13-amino-acid extension let it evade the binding proteins, stretching its reported active half-life to roughly 20 to 30 hours (Wikipedia, "IGF-1 LR3", 2026, retrieved 2026-06-15). It is a research chemical, not an approved drug.

In short, mecasermin proves that an IGF-1 medicine can exist and pass regulatory review, but only as the natural sequence, for a defined medical condition, and with a far shorter duration than the long analog. The practical takeaway is that an approved native-sequence drug like mecasermin is not interchangeable with an unapproved research analog like IGF-1 LR3, even though both raise IGF-1 signaling.

A full head-to-head on IGF-1 LR3 versus IGF-1 DES, including when each is discussed and why, is its own future spoke. We keep it at overview level here to avoid overlap: see our guide to the leading muscle-growth peptides.

What doses of IGF-1 LR3 are reported in research and community use?

Reported IGF-1 LR3 amounts cluster in the range of roughly 20 to 50 micrograms per day, with some sources describing higher research ranges; cycles are typically described as a few weeks long. These are figures people report, not a validated or recommended dose, and there is no approved human dosing for this compound.

Because there is no clinical human label for IGF-1 LR3, every number here is either a research-context figure or a community-use convention, and it should be read that way. The amounts most commonly described fall around 20 to 50 micrograms (mcg) per day, with lower starting amounts cited for first-time use and higher amounts (up to roughly 100-120 mcg in some sources) described only in an experimental context (Peptides Explorer, 2026, retrieved 2026-06-15; Swolverine, "Unlocking the Power of IGF-1 LR3", retrieved 2026-06-15). Cycle lengths described in community sources are commonly a few weeks, with the rationale that the IGF-1 receptor can become less responsive over time.

We deliberately do not publish a step-by-step dosing ladder, reconstitution math, or stacking protocol on this hub, both because IGF-1 LR3 is unapproved and because that detail belongs to a dedicated, clearly-framed spoke. For the structured version, see our peptide dosing calculator.

Our take: The "more is better" instinct is especially dangerous with IGF-1 LR3 because its risk, low blood sugar, scales with both dose and its long duration. A bigger amount does not just mean a bigger effect; it means a stronger insulin-like action that lingers for a full day. That trade-off is the whole reason to be conservative and supervised.

What amount our community logs per IGF-1 LR3 doseWhat our community logs per doseMicrograms per logged dose. A usage signal, not a dosing recommendation.196644728868252112<2020-3030-4040-5050-60>60microgram band per logged doseProtocolPlus app data: 448 trackers, 2,800 logged doses, median 40 mcg. Not a recommendation.
ProtocolPlus tracking (n = 448 users, 2,800 doses; median 40 mcg). A usage convention among people tracking the compound, not medical guidance.
Share of logged IGF-1 LR3 doses by amountMost logged doses sit in a narrow bandShare of 2,800 logged doses by microgram band. Not a recommendation.Per-doseamount40-50 mcg (~31%)30-40 mcg (~26%)20-30 mcg (~23%)50-60 mcg (~9%)<20 mcg (~7%)>60 mcg (~4%)ProtocolPlus app data (n = 2,800 doses). Usage signal only.
ProtocolPlus tracking: roughly 80% of logged doses fall in the 20-50 mcg range. A usage convention, not medical guidance.

What are the side effects of IGF-1 LR3?

The most serious risk of IGF-1 LR3 is low blood sugar (hypoglycemia), because it acts like insulin and stays active for many hours; other reported effects include joint and muscle pain, water retention, and injection-site reactions. A more theoretical, long-horizon concern is that strong, sustained growth signaling could promote the growth of abnormal cells.

Hypoglycemia is the standout because it is mechanistically built in. IGF-1 LR3 shares enough action with insulin to lower blood glucose, and unlike a fast insulin dose that clears in hours, the long half-life means that glucose-lowering pressure persists across a full day (ChemicalBook, 2024, retrieved 2026-06-15). Symptoms of low blood sugar (shakiness, sweating, confusion, in severe cases loss of consciousness) can therefore appear well after a dose and are the single most important safety issue people raise.

A hub-level overview of what sources report:

  • Most serious / dose-driven: hypoglycemia (low blood sugar), which can be delayed and prolonged because of the long half-life.
  • Commonly reported: muscle and joint pain or aches, water retention and mild swelling (edema), fatigue, and injection-site pain, redness, or swelling (Swolverine, "Side Effects of IGF-1 Peptides", retrieved 2026-06-15).
  • Theoretical / long-term: because IGF-1 signaling promotes cell growth and proliferation, there is a long-standing concern that sustained exposure could promote the growth of existing abnormal cells; this risk is discussed in the literature and is one reason the compound is not casually used (ChemicalBook, 2024, retrieved 2026-06-15).
  • Unknown: true long-term safety in humans, because there are no long-horizon human trials of IGF-1 LR3 specifically.

This is the overview, with hypoglycemia from the long half-life being the risk that matters most, alongside the theoretical growth-promotion concern that keeps the compound out of casual use.

A photorealistic close-up of a researcher's gloved hands holding an insulin syringe and a small glass vial of clear liquid, drawing a precise small dose in a clean laboratory setting.

IGF-1 LR3 is not approved by any regulator, so there is no official safety determination and no legal pathway to buy it as a medicine; the products sold online are unapproved "research chemicals," and the compound is banned in sport at all times. That status matters more than any single benefit claim.

On safety, the honest position is that no regulator has reviewed IGF-1 LR3 for human use, there are no controlled long-term human trials, and the known mechanism carries a real, built-in hypoglycemia risk plus a theoretical cancer-promotion concern. "Used by some people" is not the same as "shown to be safe." Nobody can responsibly call an unapproved growth factor with insulin-like action "safe" for general use.

On legality, the picture is specific:

  • Not an approved drug for these uses. IGF-1 LR3 is not FDA-approved for muscle growth, anti-aging, or any human use. The approved IGF-1 medicine is mecasermin (Increlex), the natural sequence, for a rare pediatric condition only (DailyMed / FDA Increlex label, retrieved 2026-06-15).
  • Sold "for research use only." The vials people buy are labeled not for human consumption, a legal and quality gray zone with no guarantee of identity, purity, or sterility.
  • Banned in sport at all times. IGF-1 and its analogs sit in WADA category S2 (peptide hormones, growth factors, and related substances), which is prohibited both in and out of competition (USADA, "IGF-1 and the World Anti-Doping Agency Prohibited List", retrieved 2026-06-15).

For the full legal framework and how to evaluate a vendor, see are peptides legal and how to vet peptide quality.

Our take: The most common misconception we see is "there's an FDA-approved IGF-1 drug, so IGF-1 LR3 must be basically fine." It is not the same molecule. Mecasermin is the natural sequence, used in a narrow childhood disorder under close monitoring. IGF-1 LR3 is a longer-lasting analog with no human approval and a stronger, longer hypoglycemia profile.

How do people obtain IGF-1 LR3?

Because IGF-1 LR3 is unapproved, there is no legitimate prescription route for personal use; people obtain it either as a laboratory cell-culture reagent or, more commonly for off-label use, as "research chemical" vials sold online. There is no third, regulated "get it from a pharmacy for fitness" option.

The legitimate supply chain is the industrial one: research-grade LONG R3 IGF-I is sold by established life-science suppliers to laboratories and biomanufacturers as a cell-culture supplement, with proper documentation. The route most consumer searches end up on is the research-peptide market, where vendors sell lyophilized IGF-1 LR3 "for research use only" and buyers reconstitute and use it off-label. That market carries real risks of mislabeled potency, impurities, and non-sterile product, with no regulatory oversight.

If someone is researching that path despite the risks, the responsible groundwork is the same as for any research peptide:

  1. Confirm the legal status for your country and situation, and remember it is banned in sport. See are peptides legal.
  2. Demand a certificate of analysis (COA) from independent third-party testing, and learn to read it. See how to vet peptide quality.
  3. Understand handling and the hypoglycemia risk before anything else. A long-acting, insulin-like compound is not forgiving of mistakes. See getting started with peptides and the peptide injections guide.
  4. Talk to a qualified clinician who can weigh your specific health situation, blood-sugar risk, interactions, and contraindications.

We are describing what people do, not endorsing it. Using an unapproved growth factor outside a research or clinical setting means accepting unknown risks with no safety net.

A realistic look at expectations

The dramatic muscle claims attached to IGF-1 LR3 come mostly from its biology and from user reports, not from controlled human trials, so expectations should be calibrated and the risks taken seriously. Going in clear-eyed is part of using any of this information responsibly.

Two honest caveats sit on top of the excitement. First, the strongest evidence for IGF-1 LR3 is its industrial track record at growing cells in a dish and IGF-1's well-understood biology, not human physique studies of this specific analog. Second, the same growth signaling that makes it interesting is exactly what raises the long-term safety questions, and the hypoglycemia risk is immediate and real. For grounded before-and-after context and how to read transformation claims, see peptides before and after. For unfamiliar terms, our peptide glossary is a quick reference.

Frequently Asked Questions

IGF-1 LR3 (Long R3 IGF-1) is a synthetic, longer-lasting analog of insulin-like growth factor 1. It has 83 amino acids versus 70 in natural IGF-1, with an arginine at position 3 and a 13-amino-acid extension. Those changes let it avoid the binding proteins that clear natural IGF-1, giving it a reported half-life of about 20 to 30 hours. It is a research chemical, not an approved drug.

The bottom line

IGF-1 LR3 is best understood as an engineering trick applied to a natural hormone: take IGF-1, the body's growth-and-repair signal, and modify it so it lasts about 20 to 30 hours instead of minutes. That durability is the entire reason it exists, and it explains both its real industrial value as a cell-culture supplement and its biggest danger as a personal compound, a long, insulin-like drop in blood sugar.

The discipline to remember is the gap between the molecule's legitimate use and its marketed one. There is an FDA-approved IGF-1 medicine, but it is the natural sequence, used in a rare childhood disorder under close monitoring, not the long analog sold online for physique goals. IGF-1 LR3 itself is unapproved, banned in sport, available only as a research chemical of uncertain quality, and untested in long-term human trials. If you take one thing from this hub, let it be that "there's an approved IGF-1 drug" does not make IGF-1 LR3 safe or legal to use. From here, the natural next reads are are peptides legal, how to vet peptide quality, and how peptides work, and for anything you might consider, a qualified clinician first.

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