IGF-1 is a powerful growth-factor hormone involved in normal growth, tissue development, and blood-sugar regulation. The approved medical form, mecasermin (INCRELEX), is used only for rare pediatric IGF-1 deficiency - not general wellness or muscle-building. Because it lowers blood sugar and drives cell growth, the same biology that makes it potent also makes it risky outside its narrow medical use.
Mecasermin is recombinant human IGF-1 (rhIGF-1). It is FDA-approved for growth failure in pediatric patients 2 years and older with severe primary IGF-1 deficiency, or GH gene deletion with neutralizing antibodies to GH - and explicitly not a substitute for GH or for secondary IGF-1 deficiency. Its use requires meal-timed dosing, glucose monitoring, and skeletal/neoplasia surveillance. Adult enhancement use is unproven, high-risk, and anti-doping prohibited.
IGF-1 is a 70-amino-acid single-chain growth factor with three intramolecular disulfide bridges (~7,649 Da), sequence-identical to endogenous human IGF-1 and produced in E. coli. It activates IGF-1R tyrosine-kinase signaling, principally PI3K-AKT-mTOR and RAS-MAPK, with systemic activity modulated by IGFBP-3 / acid-labile-subunit binding, since clearance is inversely proportional to IGFBP-3. The modified analogs IGF-1 LR3 and des(1-3) IGF-1 are distinct molecules and are kept separate throughout this page.
IGF-1 is one of the most biologically powerful molecules in this atlas and one of the most misunderstood. The clinically approved product, mecasermin, has Grade A evidence for a single narrow purpose - pediatric severe primary IGF-1 deficiency. The mechanistic case for muscle and tissue growth is real but does not equal validated adult enhancement, and the same pathways that make IGF-1 potent drive hypoglycemia and neoplasia concerns.
IGF-1 works by binding a growth-factor receptor on cells. That single action tells tissues to grow, repair, and survive - and, like insulin, to pull sugar out of the blood, which is why it can cause low blood sugar.
All of IGF-1's effects flow from IGF-1R activation, which feeds the PI3K-AKT-mTOR protein-synthesis axis and the RAS-MAPK proliferation axis. In children with true IGF-1 deficiency this drives growth-plate activity and linear growth; in everyone it carries an insulin-like glucose-lowering effect and a mitogenic signal that underlies the neoplasia caution. IGFBP-3 binding governs how long IGF-1 lasts.
IGF-1 binds IGF-1R, a receptor tyrosine kinase, triggering autophosphorylation and IRS/Shc recruitment that activates PI3K-AKT-mTOR/S6K and RAS-RAF-MEK-ERK. The same receptor biology that supports chondrocyte proliferation, myofibrillar protein synthesis, and cell survival also produces hypoglycemia (hepatic glucose suppression + peripheral uptake) and proliferation signals relevant to neoplasia. Systemic PK is dominated by IGFBP-3/ALS ternary-complex binding.
IGF-1 dosing must be split cleanly. The only defensible clinical base is the INCRELEX label - pediatric severe primary IGF-1 deficiency, SC, meal-timed, glucose-monitored. Everything else (adult enhancement, recovery, anti-aging) is off-label, experimental, and anti-doping prohibited. Working unit: mg/kg per dose, with the calculator displaying mcg and U-100 units for draw math. Native rhIGF-1 / mecasermin is the subject here; IGF-1 LR3 and des(1-3) IGF-1 are different molecules and are not dosed from this page.
0.04-0.08 mg/kg twice daily SC (40-80 mcg/kg per dose).0.04 → 0.08 → 0.12 mg/kg BID (max). Use the lowest effective tolerated dose.| Band | Dose basis | Daily exposure | Evidence basis |
|---|---|---|---|
| Low / initiation | 0.04 mg/kg BID | 0.08 mg/kg/day | FDA label starting range |
| Standard / mid | 0.08 mg/kg BID | 0.16 mg/kg/day | FDA label starting/titration range |
| High / labeled max | 0.12 mg/kg BID | 0.24 mg/kg/day | FDA maximum labeled dose |
| Non-label adult enhancement | Not established | Not established | D/P only - do not present as validated |
| Body weight | 0.04 mg/kg | 0.08 mg/kg | 0.12 mg/kg (max) |
|---|---|---|---|
| 15 kg | 0.60 mg | 1.20 mg | 1.80 mg |
| 25 kg | 1.00 mg | 2.00 mg | 3.00 mg |
| 35 kg | 1.40 mg | 2.80 mg | 4.20 mg |
| 45 kg | 1.80 mg | 3.60 mg | 5.40 mg |
| 55 kg | 2.20 mg | 4.40 mg | 6.60 mg |
| 65 kg | 2.60 mg | 5.20 mg | 7.80 mg |
| 75 kg | 3.00 mg | 6.00 mg | 9.00 mg |
| 85 kg | 3.40 mg | 6.80 mg | 10.20 mg |
| 95 kg | 3.80 mg | 7.60 mg | 11.40 mg |
| 105 kg | 4.20 mg | 8.40 mg | 12.60 mg |
This table mathematically extends label per-dose math by weight, but the approved population is pediatric severe primary IGFD. Larger body weights are shown for calculator completeness, not to imply adult-enhancement validation.
| Trigger | Action | Rationale |
|---|---|---|
| Dose tolerated ≥1 week, no hypoglycemia | Increase by 0.04 mg/kg per dose, up to 0.12 mg/kg BID | Matches FDA titration logic |
| Meal / snack skipped | Withhold the dose | Label says not to dose when a meal/snack is omitted |
| Frequent hypoglycemia symptoms | Reduce dose; continue glucose monitoring | IGF-1 has hypoglycemic effects |
| Severe hypoglycemia / seizure | HOLD - urgent medical evaluation | Severe hypoglycemia including seizures reported |
| Papilledema, visual change, headache, nausea/vomiting | HOLD - evaluate for intracranial hypertension | Label warning |
| Limp, hip or knee pain | HOLD - evaluate for slipped capital femoral epiphysis | Label warning |
| New neoplasm / malignancy | DISCONTINUE | Label: discontinue if malignant neoplasia develops |
| Closed epiphyses (growth-promotion use) | CONTRAINDICATED - stop growth-promotion use | No linear-growth benefit; label contraindication |
| Assessment | Purpose | Validated for IGF-1? |
|---|---|---|
| Preprandial glucose | Hypoglycemia safety | Yes - label-supported for initiation/titration |
| IGF-1 serum level / SDS | Exposure and disease-context tracking | Endocrine context only; not for enhancement |
| IGFBP-3 | PK / clearance context | Mechanistic, not a standalone target |
| Fundoscopic exam | Intracranial-hypertension screen | Yes - label-supported |
| Tonsil/adenoid exam, sleep-apnea symptoms | Lymphoid-hypertrophy screen | Yes - label-supported |
| Hip/knee pain assessment | SCFE screen | Yes - label-supported |
| Cancer history / neoplasm surveillance | Safety exclusion & monitoring | Yes - label warning/contraindication |
| A1c / fasting insulin / lipids | Metabolic overlay | Not validated as IGF-1 dosing control |
For research/education only. The approved product (INCRELEX) is a ready 10 mg/mL solution (40 mg / 4 mL); research vial + BAC-water rows are math only, not dosing recommendations. Native rhIGF-1 / mecasermin only - not IGF-1 LR3 or des(1-3) IGF-1.
Confirm diagnosis (severe primary IGFD or GH-gene-deletion with neutralizing antibodies), open epiphyses, preprandial glucose, IGF-1/IGFBP-3, fundoscopy, tonsil/adenoid exam, scoliosis assessment, malignancy exclusion.
Preprandial glucose monitoring until a well-tolerated dose is established; confirm meal-timed dosing and that doses are withheld when meals are missed.
Growth velocity and height SDS, hypoglycemia symptom review, hip/knee pain (SCFE), visual symptoms/headache (intracranial hypertension), snoring/sleep apnea (lymphoid hypertrophy).
IGF-1 levels for exposure context, scoliosis progression during rapid growth, fundoscopy as indicated, ongoing neoplasia surveillance.
Extra glucose vigilance with insulin or other glucose-lowering agents; additive hypoglycemia is a hard caution.
Malignant neoplasia (discontinue), severe hypoglycemia/seizure, hypersensitivity/anaphylaxis, intracranial hypertension, or closed epiphyses when used for growth promotion.
IGF-1's combinations are dominated by caution, not synergy. The GH axis naturally produces IGF-1, but mecasermin is not a GH substitute and is not for secondary deficiency. The pairings most discussed in performance circles (insulin, anabolics) compound exactly the risks - hypoglycemia, organ growth, neoplasia - that make IGF-1 hazardous, so the engine treats them as constraints.
Active malignancy or a history of malignancy is a labeled contraindication for INCRELEX, and treatment should be discontinued if malignant neoplasia develops. For page logic, flag malignancy or cancer predisposition as a hard stop, not a soft caution. Likewise, treat closed epiphyses (for growth promotion), recurrent hypoglycemia or inconsistent food intake, and competitive-sport status as exclusion conditions. And keep native rhIGF-1, IGF-1 LR3, and des(1-3) IGF-1 separate - they do not share dosing, PK, or safety claims.
IGF-1's safety profile is well documented because mecasermin is an approved drug with postmarketing surveillance. The dominant acute risk is hypoglycemia - severe enough to cause seizures and tied directly to meal timing - and the dominant chronic concern is mitogenic: a malignant-neoplasia warning that makes cancer history a hard stop. Pediatric growth use adds skeletal and lymphoid risks (SCFE, scoliosis, adenotonsillar hypertrophy, intracranial hypertension).
| Condition | Concern | Severity |
|---|---|---|
| Pediatric malignancy / history of malignancy | Labeled contraindication | Absolute |
| Current or predisposition to neoplasia | Mitogenic biology + label warning | High |
| Known hypersensitivity to mecasermin / excipients | Allergic reaction / anaphylaxis | High |
| Closed epiphyses (growth-promotion use) | No linear-growth benefit; inappropriate indication | High |
| Recurrent hypoglycemia / inconsistent food intake | Severe hypoglycemia risk | High |
| Intracranial-hypertension symptoms | Papilledema / visual risk | High |
| Active sleep apnea / tonsillar hypertrophy | Potential worsening | Medium-High |
| Hip/knee pain or limp in a growing child | SCFE evaluation needed | High |
| Scoliosis history | Monitor progression during growth acceleration | Medium |
| Concurrent insulin / glucose-lowering drugs | Additive hypoglycemia | High |
| Competitive athlete | WADA-prohibited exogenous IGF-1 | Absolute |
At initiation and through titration until a well-tolerated dose is established; the primary hypoglycemia guardrail. Reinforce meal-timed dosing.
Baseline malignancy exclusion and ongoing vigilance; discontinue on any new malignant neoplasia. Cancer history is a hard stop.
At baseline and if symptoms suggest intracranial hypertension (headache, visual change, nausea/vomiting). Hold and evaluate as needed.
Assess hip/knee pain or limp at each visit; monitor scoliosis during rapid growth. Hold and evaluate on red flags.
Tonsil/adenoid exam and sleep-apnea symptom screen for lymphoid hypertrophy; refer if obstructive symptoms develop.
Growth velocity and height SDS for efficacy; periodic IGF-1 for exposure context (not a standalone enhancement endpoint).
IGF-1 has Grade A/B clinical evidence for a single endocrine-replacement indication: pediatric severe primary IGF-1 deficiency. The mechanistic case for muscle and tissue growth is biologically strong but preclinical, and it does not translate into validated adult enhancement. The honest summary is that the same powerful biology creates the hypoglycemia, neoplasia, organ-growth, and anti-doping risks.
The label defines the indication (pediatric severe primary IGFD or GH-gene deletion with neutralizing antibodies), the SC-only meal-timed dosing (0.04-0.12 mg/kg BID), the warnings (hypoglycemia, neoplasia, intracranial hypertension, SCFE, scoliosis, lymphoid hypertrophy), and the contraindications.
An integrated clinical review describes 92 patients in Study 1419 - mostly Laron syndrome - with severe short stature and long-term mecasermin exposure, in whom mean height SDS improved during treatment. Core efficacy evidence for the approved population.
A long-term efficacy and safety analysis of recombinant human IGF-1 in children with severe IGF-1 deficiency supports growth outcomes in the indicated pediatric population, reinforcing the durability of the approved use.
Mecasermin was investigated for safety, pharmacokinetics, and exploratory outcomes in Rett syndrome - a separate research context that is not the approved growth-failure use and should not be read as enhancement evidence.
Satellite cells contribute to IGF-1-induced skeletal-muscle hypertrophy in preclinical models, and IGF-1 increases human myotube size and protein synthesis in vitro. Strong mechanism, but not validated adult clinical hypertrophy.
USADA/WADA classify all forms of exogenous IGF-1 as prohibited in and out of competition, and warn that products claiming IGF-1 may be diluted, mislabeled, or contaminated. IGF-1 sits within the peptide-hormones/growth-factors class on the WADA Prohibited List.
IGF-1 has strong clinical evidence only for a narrow endocrine-replacement indication - pediatric severe primary IGF-1 deficiency / growth failure. Mechanistic evidence for muscle growth, tissue repair, and anabolic signaling is biologically strong but does not equal validated adult-enhancement protocols. The largest concern for non-medical use is that the same mitogenic and insulin-like pathways that make IGF-1 powerful also create hypoglycemia, neoplasia, and organ-growth risk, alongside anti-doping prohibition. Native rhIGF-1, IGF-1 LR3, and des(1-3) IGF-1 must be evaluated separately.
| Evidence type | Summary | Grade |
|---|---|---|
| FDA-label clinical evidence | Approval anchored in pediatric severe primary IGFD growth-failure studies + long-term experience | A/B |
| Study 1419 / integrated review | 92 patients, mostly Laron syndrome; mean height SDS improved | B |
| Long-term rhIGF-1 treatment | Growth outcomes supported in severe IGF-1 deficiency | B |
| EU-IGFD registry | 281 patients; long-term safety surveillance | B |
| Rett syndrome exploratory | Safety/PK and exploratory outcomes; separate from approved use | B/C |
| Skeletal-muscle mechanism | PI3K-AKT-mTOR + satellite-cell biology; preclinical/in vitro | C/P |
| Anti-doping / misuse | Exogenous IGF-1 prohibited; contamination/mislabeling risk | D |
The single most important comparison on this page is internal: native rhIGF-1 (mecasermin) is not the same as IGF-1 LR3 or des(1-3) IGF-1. Those analogs were engineered to dodge IGF-binding proteins, changing their potency, duration, and risk - and they carry no comparable approval. GH/somatropin sits upstream, raising endogenous IGF-1 but indicated and dosed differently.
| Feature | IGF-1 / mecasermin | IGF-1 LR3 | Des(1-3) IGF-1 | GH / somatropin |
|---|---|---|---|---|
| Positioning | Endocrine replacement for severe primary IGFD | Modified long-Arg3 analog (research/performance) | Truncated N-terminal analog | Upstream GH therapy raising endogenous IGF-1 |
| Mechanism class | Native IGF-1R agonist | IGF-1 analog, altered IGFBP binding | IGF-1 analog, reduced IGFBP binding | GH receptor / JAK-STAT → hepatic IGF-1 |
| Evidence tier | Strongest for pediatric IGFD | Mostly preclinical / practice-pattern | Mostly preclinical | Approved for multiple GH indications |
| Route | SC only (INCRELEX) | Research injection contexts | Research contexts | SC |
| Regulatory status | FDA-approved, narrow indication; WADA banned | Not FDA-approved; distinct registry identity; WADA banned | Not approved as mainstream therapy; WADA banned | FDA-approved (specific indications); not an INCRELEX substitute |
| Binding-protein behavior | Normal IGFBP-3/ALS binding | Largely evades IGFBP binding (longer free action) | Reduced IGFBP binding | Acts via GH receptor, not IGF-1R |
| Key caution | Hypoglycemia, neoplasia, SCFE (pediatric) | Altered potency/duration; do not apply native dosing | Different binding/potency profile | Different indication and dosing; not a substitute |