Educational reference only. Informational material drawn from peer-reviewed literature. Not medical advice and not a recommendation to use, dose, or modify any therapy. Decisions about hormone therapy should be made with a qualified healthcare provider.
Overview
Overview
IGF-1 (Insulin-like Growth Factor 1) is a peptide hormone primarily produced by the liver in response to growth hormone signaling. It mediates most of the growth-promoting effects of growth hormone, including muscle protein synthesis, bone growth, and cellular proliferation.
Mecasermin is recombinant human IGF-1, sold under the brand name Increlex. It's an FDA-approved medication for treating severe primary IGF-1 deficiency in children, a rare condition where the body produces growth hormone but fails to produce IGF-1 in response.
Off-label use in adults for muscle growth, recovery, and performance enhancement exists in performance circles, though the cost of pharmaceutical Increlex makes this rare. Most off-label users actually use IGF-1 LR3 (a research peptide variant) rather than pharmaceutical mecasermin.
Forms
Available forms & half-lives
| Form | Approximate half-life |
|---|---|
| Free IGF-1 (unbound) | 10–20 minutes |
| IGF-1 bound to IGFBP-3 | 4–6 hours |
What it does
Main effects
- Muscle hypertrophy: IGF-1 directly stimulates muscle protein synthesis
- Recovery enhancement: promotes tissue repair, particularly tendons and ligaments
- Hyperplasia (new muscle cell formation): distinguishing feature from compounds that only cause hypertrophy
- Anti-aging protocols: used in some longevity practices despite mixed evidence
- Body recomposition: used in performance contexts for the anabolic and tissue-repair effects above
- Treatment of severe primary IGF-1 deficiency in children (Laron syndrome, growth hormone insensitivity syndrome): FDA-approved indication
What to watch for
Common side effects
- Hypoglycemia (severe and rapid): IGF-1 acts at insulin receptors (~1/10 potency); blood sugar can drop fast enough to cause loss of consciousness without prompt carbohydrate intake
- Tumor growth promotion: promotes cellular proliferation broadly; epidemiological studies link elevated IGF-1 with prostate, colorectal, and breast cancer risk
- Cardiac hypertrophy: with chronic supraphysiological use; cardiovascular consequences are not benign
- Organ enlargement: enlarged spleen, kidneys, tonsillar hypertrophy with long-term abuse
- Acromegaly-like features: jaw/feature changes, enlarged hands/feet with chronic high IGF-1
- Suppression of endogenous GH production via negative feedback
- Injection site reactions: multiple daily injections required due to short half-life
Key facts
Key facts worth knowing
- Hypoglycemia is rapid and severe. IGF-1 has approximately 1/10 the insulin potency at insulin receptors. At typical doses, blood sugar can drop quickly enough to cause loss of consciousness if a user doesn't eat soon after injection. A glucometer and fast-acting carbohydrate (juice, glucose tabs, candy) are non-optional. Severe hypoglycemia is a medical emergency requiring glucose or glucagon.
- FDA-approved as Increlex (2005) for severe primary IGF-1 deficiency in children (Laron syndrome, growth hormone insensitivity syndrome). Off-label adult use is not technically illegal but is uncommon due to prohibitive cost ($15,000–30,000+/month without insurance covering the medical indication). FDA. Increlex (mecasermin [rDNA origin] injection) prescribing information. Ipsen Biopharmaceuticals. Approved 2005.
- Most performance users use IGF-1 LR3, not mecasermin. LR3 is a modified version with substituted amino acids and an N-terminal extension. LR3 has dramatically longer half-life (12–15 hours vs. 10–20 minutes), doesn't bind IGFBP-3, and is more potent at any given dose. It is sold as a research peptide and is the form most commonly used in performance contexts.
- Tumor growth promotion is the central long-term concern. IGF-1 promotes cellular proliferation broadly, including any existing cancer cells. Multiple epidemiological studies link elevated IGF-1 with increased cancer risk, particularly prostate, colorectal, and breast. For users with any cancer history or risk factors, this is a serious concern.
- WADA-prohibited at all times: S2 category (Peptide Hormones, Growth Factors). Detectable in modern testing. Athletes subject to testing should not use this compound under any circumstances. WADA. Prohibited List 2024/2025. S2: Peptide Hormones, Growth Factors, Growth Factor Mimetics and Related Substances.
- Secretagogues and direct IGF-1 enter the GH axis at different points. Growth hormone secretagogues raise IGF-1 indirectly, by stimulating the pituitary's own pulsatile GH release, so hepatic IGF-1 production stays downstream of the axis's normal negative feedback. Exogenous IGF-1 bypasses that regulation: it supplies the hormone directly, and the resulting elevation suppresses endogenous GH secretion through the same feedback loop.
Legal status
Legal status
FDA-approved as Increlex (2005) for severe primary IGF-1 deficiency in children. Prescription-only in the US. Not a DEA-scheduled controlled substance. Off-label adult use is technically legal with a prescription but cost-prohibitive without insurance. Research peptide IGF-1 (including LR3) operates in a legal gray area; quality and legality vary by jurisdiction. Banned at all times by WADA (S2 category).