IGF-1 (insulin-like growth factor 1)

Two different things are sold under this name and the difference decides everything else on this page. The first is IGF-1 itself: the hormone the liver releases when growth hormone tells it to, and the thing that actually reaches a bone's growth plate and makes it lengthen. Its laboratory-made copy, called mecasermin and sold as Increlex, is an approved prescription medicine with the identical chain of 70 building blocks as the body's own version — derived here from UniProt P05019, residues 49 to 118, and cross-checked against the EU label's statement that the product is 70 amino acids in a single chain weighing 7,649 daltons. The second is IGF-1 LR3, sold by research-chemical vendors for muscle: 83 building blocks long, with one of the original 70 swapped and 13 extra bolted onto the front so that it slips past the carrier proteins that would normally hold IGF-1 in check. It is a different molecule and it is not covered by any approval anywhere.

Sold as

Injection under the skin, twice a day, in the five studies behind the approval; it must not be given into a vein. The version sold online is described as being injected under the skin or into muscle, but no published human study has given it by any route.

Legal status in the EU

Mecasermin is an approved medicine in the EU, authorised on 2 August 2007 under exceptional circumstances — meaning the disease is too rare for complete information to be obtainable — and still authorised, with the marketing authorisation now held by Esteve Pharmaceuticals in Barcelona and the product under additional safety monitoring. Its orphan designation ended in August 2017 with the ten-year exclusivity period. In the United States it has been approved since 30 August 2005 as BLA 021839. A second IGF-1 product, mecasermin rinfabate (Iplex, BLA 021884), was approved by the FDA in December 2005; its marketing status in Drugs@FDA is now Discontinued. IGF-1 LR3 has no marketing authorisation from any regulator, and neither IGF-1 nor its LR3 version appears anywhere on the FDA's list of substances nominated for pharmacy compounding under section 503A, updated 14 May 2026.

IGF-1 switches on the type 1 IGF receptor, which sits on almost every cell and looks a great deal like the insulin receptor. On the cartilage plates at the ends of growing bones that means the cells divide and enlarge, which is how a child gets taller. On muscle, fat and liver the resemblance to insulin shows: IGF-1 stops the liver making its own glucose, pushes glucose and amino acids into tissue, and can drive blood sugar too low. Because the receptor is everywhere, so is the signal — the EU label states that IGF-1 has mitogenic activity that increases the number of cells in the body, and it is that same property that underlies the tumour warning. Normally most circulating IGF-1 is held by carrier proteins, about 80 per cent of it bound to IGFBP-3; the LR3 redesign exists specifically to evade that restraint.

Part of the bodyWhat happensHow it is knownKind of evidence

The growth plates at the ends of a child's bones

This is the one thing IGF-1 is licensed to do. Long bones lengthen at a plate of cartilage near each end, and the cells in that plate divide and enlarge when IGF-1 reaches them. In children whose bodies cannot make IGF-1 — because the receptor that growth hormone docks onto is broken, so the instruction never gets through — injecting IGF-1 restarts the plate directly, bypassing the broken step. Growth hormone does not work in these children, and the label says so.

Measured in 81 children and adolescents across five studies, 75 of whom had a growth rate recorded before treatment started. They grew 2.6 cm a year before treatment and 8.0 cm a year in the first year on it. The comparison is with the same children beforehand, using paired t-tests — there was no placebo group in the pooled analysis.

Measured in people

Source [02]Source [04]

Blood sugar

IGF-1 and insulin are close relatives and their receptors look alike, so IGF-1 does part of insulin's job: it pushes sugar out of the blood into tissue and it tells the liver to stop releasing its own. The practical consequence is that an injection can drop blood sugar too far. This is why the medicine has to be given within about twenty minutes of a meal or a snack, why the dose is withheld if the child cannot eat, and why families are taught to keep glucagon — the rescue injection for a severe low — in the house.

Measured across 413 children in the clinical trial programme: 115 of them, 28 per cent, had at least one episode of low blood sugar and 6 had a seizure from it. In the smaller US analysis of 71 children followed a mean 3.9 years, 42 per cent had at least one episode, 5 needed someone else's help and 4 had a seizure or lost consciousness. In the European surveillance registry of 306 patients, episodes ran at 0.11 per patient per year of treatment and serious ones at 0.01.

Measured in people

Source [02]Source [04]Source [14]

The nerves that drive muscle, in motor neurone disease

IGF-1 keeps nerve cells alive in the laboratory, which made it one of the most-hoped-for treatments for motor neurone disease in the 1990s. It was tested three times against a dummy injection. The first trial, in North America, found people on the higher amount declining about a quarter more slowly. The second, in Europe, found no difference. The third and largest ran for two years and found no difference on anything it measured. This is not a compound waiting to be tested; it was tested, and it did not work.

Measured in three randomised, double-blind, placebo-controlled trials: 266 people over 9 months in 1997, 183 people over 9 months in 1998, and 330 people over 2 years in 2008.

Measured in people

Source [07]Source [15]Source [16]

Tonsils, adenoids and the gland behind the breastbone

IGF-1 does not only grow bone. Lymph tissue grows too, and the tissue that grows most visibly sits at the back of the throat. Tonsils and adenoids enlarge, mostly in the first year or two of treatment, and the consequences are the ordinary ones of a blocked airway in a child: snoring, pauses in breathing during sleep, and fluid behind the eardrum that needs a drainage tube. The thymus, a gland behind the breastbone, also enlarges. The EU label tells doctors to examine for this on a schedule rather than waiting for a complaint.

Measured in the same 413-child trial programme: enlarged tonsils in 38 children (9 per cent), snoring in 30 (7 per cent), and ear-tube insertion, sleep apnoea, enlarged adenoids, middle-ear fluid, hearing loss and thymus enlargement all listed as common, meaning between 1 in 100 and 1 in 10.

Measured in people

Source [02]

Pressure inside the skull

Fluid pressure around the brain can rise. It shows up as headache, feeling sick, being sick, changes in vision, and a swelling at the back of the eye that an eye examination can see. It is the same problem that growth hormone treatment can cause. It settled in every case once the injections were paused; two children never restarted and two restarted on a smaller amount without it returning.

Measured in 4 of 413 children in the trials — 0.96 per cent — all of them children aged 7 to 9 who had not been treated before. All four recovered without lasting damage.

Measured in people

Source [02]

Muscle — but only the muscle it physically reaches

This is the claim the whole gray market is built on, and the one human experiment that measured it directly produced a result that cuts against the way the compound is sold. IGF-1 was infused into the artery feeding one forearm for six hours. In that forearm, muscle built new protein faster and, at the higher amounts, broke down existing protein more slowly. The other arm of the same person — reached by the same IGF-1 arriving through the bloodstream, at levels up to 517 nanograms per millilitre — did nothing at all: no change in how it handled sugar, lactate or protein.

Measured across the forearm in 19 people in a single laboratory study published in 1994, with each person's opposite arm acting as the comparison. No study has ever measured what injecting IGF-1 does to muscle size or strength in a healthy adult, and no study of any kind has given IGF-1 LR3 to a person.

One small study

Source [08]Source [09]

Cells that are already dividing

IGF-1's job is to tell cells to grow and to keep them from dying, and it says that to almost every cell in the body, not only the ones a person wants bigger. That is why the EU label bars the medicine outright in any child with a tumour or a suspected tumour, or with anything in their history that raises the risk of one, and tells doctors to stop treatment permanently if a tumour appears. In rats given it every day for two years, tumours of the adrenal gland, the skin and the breast appeared, some of them at exposures no higher than a treated child's.

Not measured as a rate in people. The label's warning rests on reports sent in voluntarily after approval — a mixture of cancers including some rarely seen in children — from a treated population whose size nobody knows, so no rate can be calculated from them. The dose-response evidence is the two-year rat study. The human numbers that exist measure the body's own IGF-1 level, not an injected one, and are reported separately below.

Only seen in animals

Source [02]Source [04]

The approval belongs to only one of the two things on this page: mecasermin, licensed for children aged 2 to 18 whose bodies cannot make enough IGF-1 of their own, while IGF-1 LR3 — the version sold online for muscle — has never been given to a human being in any published study, at any amount, for any purpose. Where IGF-1 has been tested against a dummy injection for something else, it failed: 330 patients with motor neurone disease, randomised for two years, showed no difference from placebo on the muscle-strength score or on survival without a breathing tube, and the 1998 European trial in 183 patients found no difference either. Only the earliest of the three, 266 patients over 9 months in 1997, found anything — 26 per cent slower decline on the higher amount against placebo, never reproduced. The growth approval itself rests on a comparison a reader should know about: in the 75 of 92 treated children who had a growth rate on record beforehand, height velocity was 8.0 cm a year in the first year against 2.6 cm a year in the same children before treatment, compared by paired t-test, with no placebo group in the pooled analysis. It fades to 5.9, 5.5 and eventually 4.4 cm a year by year 8. On the muscle claim the only direct human measurement infused IGF-1 into one forearm artery for six hours in 19 people: that arm built protein 49 to 74 per cent faster, and the same person's other arm, reached by the same IGF-1 through the bloodstream, changed in no way at all. A PubMed search of the four common LR3 spellings returned 86 records and none with the clinical-trial publication type; ClinicalTrials.gov returns zero registered studies.

Injected under the skin, IGF-1 is almost completely absorbed — bioavailability was around 100 per cent in healthy volunteers — and it leaves slowly for a molecule this size: the terminal half-life was about 5.8 hours after a single 0.12 mg/kg injection, measured in three children. How fast it clears depends on how much of the carrier protein IGFBP-3 a person has, which is why children with the deficiency clear it faster than healthy people do. The effects run on several different clocks. Low blood sugar is most frequent in the first month, which is why glucose is checked before meals until a tolerated amount is found. Tonsils and adenoids grow mostly in the first one to two years and less afterwards. Growth itself is front-loaded and then fades: 8.0 cm in year 1 against 2.6 cm a year before treatment, then 5.9, 5.5, 5.2, 4.9, 4.8, 4.3 and 4.4 cm in years 2 to 8 — every year above the starting rate, none of them close to the first. Reaching final height took an average of 11 years of treatment in the trials and a median of 3.9 years in the real-world registry, where children started much later. Against motor neurone disease, 9 months produced a result once and no result the second time, and 2 years produced nothing at all. For IGF-1 LR3 there is no time course, because there is no human study to take one from.

What was measuredWhat happenedIn whomHow it is known

How fast children with severe IGF-1 deficiency grew

8.0 cm in the first year of treatment against 2.6 cm a year in the same children before it started — a gain of 5.4 cm a year, p below 0.0001 on a paired t-test. The comparison is each child against their own earlier growth rate; the pooled analysis had no placebo group. The effect shrank each year afterwards and stayed above the starting rate: 5.9 cm in year 2, 5.5 in year 3, and 4.4 by year 8, when 19 children were still being followed.

81 children and adolescents with severe primary IGF-1 deficiency across five studies, average age 6.8 years, average height 6.9 standard deviations below normal; 75 had a pre-treatment growth rate on record

Measured in people

Source [02]

Height at the end of growing

About 13 cm taller, plus or minus 8 cm, than the height expected for untreated Laron syndrome. The comparison is against what people with the same untreated condition reach, not against a randomised control group, and the spread of 8 cm is wide relative to the 13 cm difference.

21 previously untreated subjects who reached near-adult height, after an average of 11 years of treatment

Measured in people

Source [02]

Height at the end of growing, in ordinary clinical practice rather than a trial

An average gain of 0.9 standard deviations of height between starting treatment and finishing growing, and 1.4 standard deviations in the children who had never been treated before and had not yet started puberty. Almost half of that untreated-and-prepubertal group finished within the normal height range, against 10.5 per cent of the children who had Laron syndrome. The registry has no untreated comparison group; the contrast is between subgroups within it.

102 patients in the global Increlex Growth Forum Database registry (NCT00903110) who reached near-adult height by April 2023, average age 11.8 years at the start, median 3.9 years of treatment

Measured in people

Source [17]

Muscle strength and survival in motor neurone disease, the largest and longest test

No difference from a dummy injection on anything measured — not on the strength score that was the main outcome, and not on survival without a breathing tube or on the disease rating scale. The paper's conclusion is one sentence: IGF-1 does not provide benefit for patients with amyotrophic lateral sclerosis.

330 patients at 20 medical centres, randomised to 0.05 mg per kg of body weight twice daily under the skin or to placebo, for 2 years, analysed by intention to treat

Measured in people

Source [07]

Disease progression in motor neurone disease, the European test

No significant difference between IGF-1 and a dummy injection on the rating scale that was the main outcome.

183 patients at eight European centres, 124 on 0.1 mg per kg per day under the skin and 59 on placebo, for 9 months

Measured in people

Source [15]

Disease progression in motor neurone disease, the one trial that found something

Loss of function ran 26 per cent slower on the higher amount than on a dummy injection, p equal to 0.01, with quality of life declining more slowly too. The lower amount pointed the same way without reaching significance. Neither of the two later trials reproduced it: the European one, smaller at 183 patients and the same 9 months, and the 330-patient trial that ran more than twice as long.

266 patients at eight North American centres, randomised to 0.05 mg/kg/day, 0.10 mg/kg/day or placebo, for 9 months

Measured in people

Source [16]

Breast cancer, and the body's own IGF-1 level

Women with more IGF-1 circulating naturally got more breast cancer: a hazard ratio of 1.11 per 5 nmol/l higher, with a range from 1.07 to 1.16, against women with less. A genetic analysis designed to test whether the link is causal pointed the same way but far more weakly — an odds ratio of 1.05, range 1.01 to 1.10, only just excluding no effect. This is about the amount a body makes for itself. Nobody has measured what injecting it does.

206,263 women in UK Biobank followed a median 7.1 years with 4,360 breast cancers, plus a genetic analysis using 122,977 cases and 105,974 controls

Measured in people

Source [18]

Cancer and diabetes in people who make almost no IGF-1 at all — the mirror image

One non-fatal cancer and no cases of diabetes among people with a broken growth hormone receptor, against 17 per cent with cancer and 5 per cent with diabetes among their unaffected relatives in the same community. This is an observational family comparison over 22 years, not an experiment, and the two groups differ in more than their IGF-1.

An Ecuadorian community carrying growth hormone receptor mutations, monitored for 22 years, compared with unaffected relatives

Measured in people

Source [19]

Blood sugar control in teenagers with type 1 diabetes, added on top of insulin

Average blood sugar over three months (HbA1c) fell on the higher amount compared with a dummy injection, p equal to 0.03, with the biggest median fall of 0.6 percentage points from the starting value at week 12 — and it had faded by week 24. There was no difference from placebo in body mass index, insulin dose or how often blood sugar went too low.

53 people aged 10.8 to 20.6 with type 1 diabetes of more than two years, randomised to 20 or 40 micrograms per kg per day or placebo on top of multiple daily insulin injections, 24 weeks

One small study

Source [20]

Muscle protein, in the arm the IGF-1 was infused into

The rate at which the forearm built new muscle protein rose by 49 to 74 per cent at all three amounts tested, and at the two higher amounts the rate of breakdown fell by about 45 per cent. The comparison that matters is the person's other arm: it received the same IGF-1 through the bloodstream, up to 517 nanograms per millilitre, and its handling of sugar, lactate and protein did not change at all.

19 people who had not eaten, given 1.8, 6.0 or 10.0 micrograms per kg per hour into one forearm artery for 6 hours

One small study

Source [08]

Body composition in healthy older women

Fat fell in all three groups against their own two-week baseline on a fixed diet. Lean tissue rose only in the higher-IGF-1 group and the growth hormone group, not in the lower-IGF-1 group. There was no placebo arm, so nothing here is a comparison against not being treated. The two groups that gained lean tissue were also the two that reported headaches, tiredness, swollen and painful joints and bloating; the lower amount, which changed nothing, was tolerated.

16 healthy women averaging 71.9 years, split between growth hormone (5), 0.015 mg/kg IGF-1 twice daily (6) and 0.060 mg/kg IGF-1 twice daily (5), for 4 weeks

One small study

Source [21]

Anything at all, for IGF-1 LR3

Nothing has been measured, because there has been nothing to measure it against. No published study has given IGF-1 LR3 to a person, so there is no treated group, no comparison group and no result — not for muscle, not for strength, not for fat, not for safety.

None. A PubMed search of the four common spellings returned 86 records and none with the clinical-trial publication type; a ClinicalTrials.gov search returned no registered study

Claimed, never tested

Source [09]Source [11]

Blood sugar falling too far is the dominant risk, because IGF-1 does part of insulin's job: 115 of 413 children in the trials, 28 per cent, had at least one episode and 6 had a seizure from it, which is why the injection is timed to a meal, withheld if the child cannot eat, and why families keep the rescue injection glucagon at home. The EU label states an increased risk of benign and malignant tumours and bars the medicine outright for any child with a tumour, a suspected tumour, or a history that raises the risk of one — a warning built from voluntary post-approval reports with no denominator, alongside a two-year rat study in which adrenal, skin and breast tumours appeared. Severe allergic reactions including anaphylaxis requiring hospital admission have been reported. Raised pressure inside the skull occurred in 4 of 413 children. Tonsils enlarge in about 9 per cent, enough to block breathing at night. Thickened lumps at injection sites occurred in 17 per cent, and headache in 44 per cent. None of these figures has ever been measured in a healthy adult, and for IGF-1 LR3 there is no safety record at all — the only black-market vial ever chemically analysed and published contained the protein with a laboratory purification tag still attached, whose effects in humans the analysts said had never been described. IGF-1 is prohibited in sport at all times.

EffectWhat it feels likeHow often

Blood sugar falling far enough to cause a seizure or loss of consciousnessSerious

IGF-1 acts partly like insulin, so it can take blood sugar down past where it should stop. Episodes were most frequent in the first month and in the youngest children, and 47 per cent of those who had them had a history of low blood sugar before treatment. The label instructs that the injection be given within about twenty minutes of food, be withheld entirely if the child cannot eat, and never be doubled up to make up a missed dose, and that families keep glucagon — the emergency injection that raises blood sugar — at home.

Low blood sugar is listed as very common in the EU label, meaning more than 1 in 10, and a seizure from it as common, meaning between 1 in 100 and 1 in 10. In numbers: 115 of 413 children (28 per cent) had at least one episode and 6 had a seizure. In the US analysis of 71 children followed a mean 3.9 years, 30 (42 per cent) had an episode, 5 needed another person's help and 4 had a seizure or lost consciousness.

Source [02]Source [04]Source [14]

Tumours, both the harmless kind and the dangerous kindSerious

IGF-1 tells cells to divide and to stay alive, which is also what a tumour needs. The EU label states there is an increased risk in treated children, names a mixture of cancers including rare ones not usually seen in children, and bars the medicine completely in any child with a tumour, a suspected tumour, or a history that raises the risk of one. Treatment is to be stopped permanently if a tumour appears. The label adds that the risk is likely higher when the medicine is used outside its licence or above the licensed amount.

No frequency can be given. The EU label lists benign and malignant tumours under reports received after approval, where the size of the treated population is unknown, so no rate exists.

Source [02]Source [04]

A severe allergic reactionSerious

The EU label names hives, swelling under the skin and difficulty breathing, and says some cases were indicative of anaphylaxis and required admission to hospital. Reactions can be confined to the injection site or affect the whole body. On re-exposure the symptoms did not always come back. Families are told that if a whole-body reaction happens, the injections stop and they seek help immediately.

In trials of other conditions covering about 300 patients, 8 per cent had a local or whole-body allergic reaction, all of them mild or moderate and none serious. The severe reactions are all from reports after approval, where the EU label gives no frequency at all.

Source [02]Source [04]

Raised pressure inside the skullSerious

Headache, feeling sick, being sick, changes in vision, and swelling at the back of the eye that an eye examination picks up. All four children recovered fully once dosing was interrupted; two never restarted and two restarted on less without it returning. The label asks for an eye examination when treatment starts, on a schedule afterwards, and whenever symptoms appear.

Listed as uncommon in the EU label, meaning between 1 in 1,000 and 1 in 100. It happened to 4 of 413 children in the trials, 0.96 per cent.

Source [02]

The growth plate at the hip slipping, and a curved spine getting worseSerious

Both are known problems of growing fast, whatever is driving the growth, and both appear in the growth hormone labels too. A slipped growth plate at the top of the thigh bone can cut off the blood supply to the bone and kill it. The signal is a child starting to limp or complaining of hip or knee pain, and the label says any child who does should be examined for it. Existing curvature of the spine can also progress and is to be monitored.

Not given as a rate in either the EU or the US label.

Source [02]Source [04]

The preservative in the vial, in babiesSerious

Each millilitre contains 9 mg of benzyl alcohol as a preservative. The EU label bars the product completely in premature babies and newborns because of it, and warns of toxic and allergy-like reactions in children up to three years old. The US label states that benzyl alcohol has been associated with serious reactions including death in newborns and infants, and that the product is not recommended in infants.

Not given as a rate.

Source [02]Source [04]

Tonsils and adenoids enlarging, and a blocked airway at night

Most of it happens in the first one to two years and slows afterwards. It matters because a child with enlarged tonsils and adenoids stops breathing properly in their sleep and collects fluid behind the eardrum, which can end in surgery. The label asks for periodic examination rather than waiting for a complaint.

Enlarged tonsils in 38 of 413 children (9 per cent) and snoring in 30 (7 per cent). Sleep apnoea, enlarged adenoids, middle-ear fluid, hearing loss and insertion of an ear tube are each listed as common, meaning between 1 in 100 and 1 in 10.

Source [02]

Headache, being sick, and ear infections

A headache in a child on this medicine is usually just a headache, but it is also the first symptom of raised pressure inside the skull, which is why the label asks for an eye examination when symptoms appear rather than treating headache on its own.

Headache was the single most reported effect in the trials at 44 per cent, being sick at 26 per cent and middle-ear infection at 17 per cent. All three are listed as very common in the EU label, meaning more than 1 in 10.

Source [02]

Lumps of thickened tissue where the injections go

It was generally down to injecting into the same patch repeatedly, and it cleared up when the injections were spread around properly. The label instructs rotating between upper arm, thigh, buttock and abdomen with every injection. Pain, redness, swelling, hardening and bleeding at the site are listed as common.

Injection site hypertrophy occurred in 71 of 413 children, 17 per cent, and is listed as very common along with bruising at the site.

Source [02]Source [04]

Joint and limb pain

The same complaint appears in the growth hormone labels and was one of the things the healthy older women in the 1995 body-composition study reported on the higher amount, alongside headaches, tiredness and bloating — while the group on the lower amount, in whom nothing changed, tolerated it.

Joint pain and pain in the arms and legs are both listed as very common in the EU label, meaning more than 1 in 10. Muscle pain is common.

Source [02]Source [21]

Changes to the heart

The EU label recommends a scan of the heart before treatment starts, another when it stops, and regular scans for anyone with an abnormal result or heart symptoms. No study has followed what happens to these findings afterwards.

A heart murmur and a fast heartbeat are listed as common, between 1 in 100 and 1 in 10. An enlarged heart, thickened heart muscle and leaking mitral or tricuspid valves are listed as uncommon, between 1 in 1,000 and 1 in 100.

Source [02]

Not knowing what is in the vial, for anything bought outside a pharmacy

Analytical chemists took an injection vial obtained on the black market and identified what was in it: Long-R3-IGF-I carrying a six-histidine tag on its tail, a laboratory purification handle that has no business being injected into a person. Their conclusion was that the contents were more likely a by-product of biochemical research than something made for injection, and that the effects of this His-tagged version in humans have never been described.

Not measured. One black-market vial has been analysed and published; nobody has surveyed the market.

Source [10]

These are the amounts the studies below gave their participants, and they are here as facts about those studies. They are not a recommendation, not a starting point and not a range to pick from. What a person should take, if anything, is a question for a doctor who knows them.

The five studies behind the approval, in children and adolescents with severe primary IGF-1 deficiency. Four were open-label and one was double-blind and placebo-controlled; the pooled growth analysis compares each child with their own rate before treatment.

Generally 60 to 120 micrograms per kg of body weight, injected under the skin twice a day. The greatest growth was seen at 120 micrograms per kg twice daily.

Up to 8 years. 92 children received these doses, 81 were in the efficacy analysis and 75 had a growth rate on record beforehand; 19 were still being measured at year 8

Source [02]

The phase III trial in motor neurone disease that ran longest, which found no difference from a dummy injection.

0.05 mg per kg of body weight twice daily, injected under the skin, against placebo

2 years, in 330 patients across 20 centres

Source [07]

The two earlier placebo-controlled trials in motor neurone disease — the North American one that found a difference and the European one that did not.

North America: 0.05 or 0.10 mg per kg per day under the skin, against placebo. Europe: 0.1 mg per kg per day under the skin, against placebo.

9 months in each; 266 patients in North America, 183 in Europe

Source [15]Source [16]

The randomised, placebo-controlled trial of IGF-1 added on top of insulin in teenagers with type 1 diabetes.

20 or 40 micrograms per kg per day under the skin, against placebo

24 weeks, in 53 people aged 10.8 to 20.6

Source [20]

The only direct measurement of what IGF-1 does to human muscle, made by infusing it into the artery feeding one forearm while the other arm served as the comparison.

1.8, 6.0 or 10.0 micrograms per kg per hour, infused into one forearm artery

6 hours, in 19 people who had not eaten

Source [08]

The four-week body-composition study in healthy older women, which had three active groups and no placebo group.

0.015 or 0.060 mg per kg twice daily under the skin, alongside a third group given growth hormone at 0.025 mg per kg per day

4 weeks, after a 2-week baseline, in 16 women averaging 71.9 years on a fixed diet

Source [21]

What people report

• Whether IGF-1 LR3 does anything at all in a human body — no published study has ever given it to a person, at any amount, for any purpose
• Where the 20 to 40 microgram daily figure circulating online came from — no human study of IGF-1 LR3 exists to have produced it, and the review that recorded the pattern notes that even the route and the half-life are undocumented in humans
• Whether the approved medicine beats no treatment at all — the growth figures behind the licence compare each child with their own rate before treatment, and no placebo-controlled growth trial has been published
• How much of that first-year jump from 2.6 to 8.0 cm is the medicine and how much is catch-up growth a very short child would have had anyway
• Whether giving IGF-1 to a person raises their cancer risk — the label's warning is built from voluntary reports with no denominator, the dose-response data are from rats, and the human numbers measure the body's own level rather than an injected one
• What IGF-1 does to muscle in a healthy adult who injects it — the only direct human measurement infused it into one forearm artery for six hours, and the opposite arm, reached through the bloodstream, changed in no way at all
• Whether IGF-1 increases strength — no published study of any kind has measured it
• Why the one positive motor neurone disease trial was positive — 266 people showed 26 per cent slower decline against placebo, and neither the smaller European trial nor the larger two-year 330-person trial reproduced it
• What is actually in vials sold as IGF-1 LR3 — one has been analysed and published, and it contained a research protein with a purification tag still attached; nobody has surveyed the market
• What happens beyond about eleven years of treatment, or at any age in adulthood — the licence stops at 18, and the way the body handles it has not been studied above 65 or below 12
• Whether it is safe in pregnancy — the EU label states there are limited or no data in pregnant women, that the animal work is insufficient, and that it should not be used
• Whether the heart changes the label lists as uncommon — enlargement, thickened muscle, leaking valves — go anywhere afterwards; a scan is required before and after treatment and no study has followed what it found
• How often the serious harms happen outside the licensed group, because every frequency in the label comes from 413 children with a rare growth disorder taking it under supervision with food timed around each injection
• Whether the thickened lumps at injection sites make absorption unpredictable the way they do with insulin — 17 per cent of treated children got them and nobody followed what happened to those children next
• Whether IGF-1 and growth hormone taken together, which is what the gray market actually does, is better or worse than either alone — never tested
• What happened to the second approved IGF-1 product — mecasermin rinfabate (Iplex) was approved by the FDA in December 2005 and its marketing status is now Discontinued, with no published trial result on record to explain why

Does IGF-1 actually build muscle?

Nobody has shown that injecting it builds muscle in a healthy person, and the one experiment that measured it directly is discouraging. IGF-1 was infused into the artery of one forearm in 19 people: that forearm built protein faster and broke it down more slowly, while the other arm of the same person — reached by the identical IGF-1 through the bloodstream — showed no change at all. The only body-composition study, in 16 healthy older women over four weeks, did find lean tissue rising on the higher amount, but it had no placebo group and the same group reported headaches, tiredness, swollen painful joints and bloating. No study has ever measured strength.

Source [08]Source [09]Source [21]

Is IGF-1 LR3 the same thing as the approved IGF-1 medicine?

No, and the difference is the most important fact on this page. The approved medicine, mecasermin, is a copy of human IGF-1 with exactly the same 70 building blocks as the version your own body makes. IGF-1 LR3 is 83 building blocks long: one of the original 70 has been swapped, and 13 extra have been bolted onto the front, specifically so it slips past the carrier proteins that would normally hold IGF-1 in check. That makes it a different molecule with a different behaviour in the body, and no published study has ever given it to a person — so the approval of the medicine says nothing whatsoever about it.

Source [01]Source [02]Source [09]Source [13]

What are the side effects of IGF-1?

The one that dominates is blood sugar dropping too far, because IGF-1 acts partly like insulin: 28 per cent of the 413 children in the trial programme had at least one episode and 6 of them had a seizure from it. After that come headache in 44 per cent, being sick in 26 per cent, thickened lumps at the injection sites in 17 per cent, ear infections in 17 per cent, and enlarged tonsils in 9 per cent — enough, in some children, to block breathing at night. Rarer but more serious are raised pressure inside the skull, which happened to about 1 in 100, severe allergic reactions, and tumours, which the label lists without a frequency because nobody knows how many treated children the reports came from. Every one of these numbers comes from children with a rare growth disorder taking a licensed medicine under supervision; none of it has been measured in an adult using it for muscle.

Source [02]Source [04]

Is IGF-1 legal, and is it banned in sport?

Mecasermin is a legal prescription medicine in the EU and the United States, for one rare condition in children — a doctor prescribes it, a pharmacy dispenses it. IGF-1 LR3 has no marketing authorisation from any regulator, so it is not a legal medicine anywhere; it circulates labelled as a research chemical. In sport there is no ambiguity at all: the World Anti-Doping Agency's 2026 Prohibited List names 'Insulin-like growth factor 1 (IGF-1, mecasermin) and its analogues' under section S2.3, prohibited at all times, in and out of competition, as a non-specified substance. 'And its analogues' is what covers the LR3 version.

Source [03]Source [05]Source [12]

IGF-1 vs HGH — what is the difference?

They are two links in the same chain. Growth hormone is the instruction the pituitary gland sends out; IGF-1 is what the liver makes when it receives that instruction, and IGF-1 is what actually reaches a bone's growth plate and makes it grow. That is why they are not interchangeable: children whose growth hormone receptor is broken cannot turn growth hormone into IGF-1, so growth hormone does nothing for them and the EU label says explicitly that mecasermin is not a substitute for growth hormone treatment, and vice versa. The other difference is what happens to blood sugar. Growth hormone pushes it up; IGF-1, being an insulin relative, pulls it down, which is why the main danger of one is the opposite of the other.

Source [02]Source [21]

Does IGF-1 cause cancer?

The honest answer has three parts and none of them is a clean yes or no. In people, the amount of IGF-1 a body makes for itself tracks with breast cancer risk: across 206,263 women, each 5 nmol/l more came with an 11 per cent higher rate, and a genetic analysis designed to test causation found a much smaller effect that only just excluded zero. In rats given it daily for two years, tumours of the adrenal gland, skin and breast appeared. In treated children, the EU label states an increased risk and bars the medicine for anyone with a tumour or a history that raises the risk of one — but that statement rests on reports sent in voluntarily after approval, from a population whose size nobody knows, so it is not a rate. What nobody has done is measure cancer in a trial of people given IGF-1.

Source [02]Source [18]Source [19]

Can you buy IGF-1?

The approved medicine, only on prescription and effectively only for the rare childhood condition it is licensed for. Everything sold online as IGF-1 or IGF-1 LR3 is an unapproved product with no manufacturing oversight, and the one vial that has been chemically analysed and published turned out to contain a laboratory version of the protein with a purification tag still attached — something the analysts judged more likely to be a research by-product than a product made for injection, and whose effects in a human being have never been described. Neither IGF-1 nor IGF-1 LR3 appears anywhere on the US regulator's list of substances nominated for pharmacy compounding, updated 14 May 2026.

Source [02]Source [10]Source [22]

Each letter represents one amino acid.

1. [01]UniProt P05019 — human insulin-like growth factor 1; mature chain residues 49–118 gives the verified 70-residue one-letter sequence
2. [02]European Medicines Agency — Increlex (mecasermin), product information: indication, posology, contraindications, section 4.8 undesirable effects and section 5.1 Table 2 annual height results
3. [03]European Medicines Agency — Increlex EPAR: authorised, marketing authorisation issued 02/08/2007, holder Esteve Pharmaceuticals S.A., authorised under exceptional circumstances, under additional monitoring (2007)
4. [04]DailyMed — INCRELEX (mecasermin) injection, US prescribing information: contraindications, warnings, and section 6.1 clinical trials experience (hypoglycaemia in 30 of 71 subjects, 42 per cent)
5. [05]Drugs@FDA — INCRELEX, BLA 021839, original approval 30 August 2005, marketing status Prescription (2005)
6. [06]Drugs@FDA — IPLEX (mecasermin rinfabate recombinant), BLA 021884, original approval 12 December 2005, marketing status Discontinued (2005)
7. [07]Sorenson EJ et al. Subcutaneous IGF-1 is not beneficial in 2-year ALS trial, Neurology 2008;71(22):1770-5 (330 patients, randomised, double-blind, placebo-controlled, no difference on primary or secondary outcomes) (2008)
8. [08]Fryburg DA. Insulin-like growth factor I exerts growth hormone- and insulin-like actions on human muscle protein metabolism, Am J Physiol 1994;267(2 Pt 1):E331-6 (19 subjects; infused forearm responded, contralateral forearm did not) (1994)
9. [09]Dominikowski A et al. The emerging landscape of performance-enhancing peptides modulating the GH-IGF1 axis, Front Endocrinol 2026;17:1822475 (IGF-1 LR3 placed in the lowest evidence tier: no peer-reviewed human studies; describes the Glu3→Arg substitution and N-terminal extension) (2026)
10. [10]Kohler M et al. Detection of His-tagged Long-R³-IGF-I in a black market product, Growth Horm IGF Res 2010;20(5):386-90 (2010)
11. [11]ClinicalTrials.gov API v2, query.term="IGF-1 LR3": totalCount 0, checked 3 August 2026 ("Long R3 IGF-1" and "Long R3 IGF-I" also return 0)
12. [12]WADA World Anti-Doping Code International Standard — Prohibited List 2026, section S2.3: "Insulin-like growth factor 1 (IGF-1, mecasermin) and its analogues", prohibited at all times, non-Specified (2026)
13. [13]Laajoki LG et al. Solution structure and backbone dynamics of Long-[Arg3]insulin-like growth factor-I, J Biol Chem 2000;275(14):10009-15 — the source for LR3's Glu3→Arg substitution and its 13-amino-acid N-terminal extension, i.e. 83 residues against IGF-1's 70 (2000)
14. [14]Frequency and predictive factors of hypoglycemia in patients treated with rhIGF-1: data from the Eu-IGFD registry, Journal of Clinical Endocrinology and Metabolism (2023)
15. [15]Borasio GD et al. A placebo-controlled trial of insulin-like growth factor-I in amyotrophic lateral sclerosis, European ALS/IGF-I Study Group, Neurology (1998)
16. [16]Lai EC et al. Effect of recombinant human insulin-like growth factor-I on progression of ALS. A placebo-controlled study, North America ALS/IGF-I Study Group, Neurology (1997)
17. [17]Ramon-Krauel M et al. Near-adult height outcomes in patients treated with rhIGF-1 for severe growth failure: real-world IGFD registry data, Journal of Clinical Endocrinology and Metabolism (2026)
18. [18]Murphy N et al. Insulin-like growth factor-1, insulin-like growth factor-binding protein-3, and breast cancer risk: observational and Mendelian randomization analyses with ~430,000 women, Annals of Oncology (2020)
19. [19]Guevara-Aguirre J et al. Growth hormone receptor deficiency is associated with a major reduction in pro-aging signaling, cancer, and diabetes in humans, Science Translational Medicine (2011)
20. [20]Acerini CL et al. Randomised placebo-controlled trial of human recombinant insulin-like growth factor I plus intensive insulin therapy in adolescents with insulin-dependent diabetes mellitus, The Lancet (1997)
21. [21]Thompson JL et al. The effects of recombinant human insulin-like growth factor-I and growth hormone on body composition in elderly women, Journal of Clinical Endocrinology and Metabolism (1995)
22. [22]FDA — Bulk Drug Substances Nominated for Use in Compounding Under Section 503A, updated 14 May 2026 (no IGF-1 or IGF-1 LR3 entry in any category) (2026)