Recombinant human IGF-1, sold as Increlex. FDA-approved twice-daily injection for children who cannot make IGF-1 and grow very slowly.
Also called Increlex, rhIGF-1, rhIGF-I, Recombinant human IGF-1, Insulin-like growth factor 1, IGF-1, Somatomedin C, Iplex (mecasermin rinfabate)
When Mecasermin's status or evidence changes, it's in the next morning's email.
Mecasermin is lab-made human insulin-like growth factor 1 (IGF-1), with the same 70 amino acids as the body's own. Normally the pituitary releases growth hormone, the liver answers by making IGF-1, and IGF-1 drives most of a child's growth in height. Some children make plenty of growth hormone but little IGF-1, most often because of Laron syndrome, where the growth hormone receptor does not work. Growth hormone injections do nothing for them. Mecasermin supplies the missing IGF-1 directly. Sold as Increlex, FDA approved it in August 2005 for children 2 and older with severe primary IGF-1 deficiency.
The evidence comes from small open-label studies, which is expected for a disease this rare. In 76 children treated for up to 12 years, growth rose from 2.8 cm a year to 8.0 cm a year in the first year, then settled lower but stayed above baseline for up to 8 years. In 21 children treated to adult height, they ended a mean 13.4 cm taller than predicted, though most still finished below the normal adult range.
Because IGF-1 acts a lot like insulin, low blood sugar is the main risk: 42% of children had at least one episode in trials, and 4 had seizures or passed out. The dose must be given within 20 minutes of a meal. Enlarged tonsils, raised pressure in the skull and cases of cancer reported after approval are on the label. Outside this use, trials in ALS (330 patients) and Duchenne muscular dystrophy (17 boys treated) found no benefit to muscle function. Eton Pharmaceuticals bought the US rights from Ipsen in December 2024.
What it binds to, and what happens inside the body after that, step by step.
Mecasermin activates the type 1 IGF receptor, which is closely related to the insulin receptor. In growth plates this drives the cell growth that lengthens bones. It also pushes glucose, fatty acids and amino acids into tissues, which is why it can drop blood sugar like insulin. In children with severe primary IGF-1 deficiency it replaces the IGF-1 their liver does not make despite normal or high growth hormone.
Human results and animal results are kept apart below. A result in rats tells you a mechanism is plausible. It does not tell you what happens in a person.
FDA-approved on open-label data: in children with severe primary IGF-1 deficiency, mecasermin roughly triples growth rate in the first year and adds about 13 cm to adult height. Outside that use, randomized trials in ALS and Duchenne muscular dystrophy found no benefit to muscle function, and a 6-week study in type 2 diabetes lowered blood sugar but caused significant side effects in some patients, and only half finished it. There is no human evidence for bodybuilding, fat loss or anti-aging use.
76 children with growth hormone insensitivity, up to 12 years
Growth rose from 2.8 to 8.0 cm a year in year 1; low blood sugar in 49%, lipohypertrophy 32%, tonsil or adenoid enlargement 22%.
Read the study21 children treated to adult or near-adult height, mean 10 years
Mean adult height 13.4 cm above that expected without treatment; most still below the normal adult range.
Read the study330 people with ALS, 2 years, double-blind
No difference from placebo in muscle strength, function or tracheostomy-free survival at 0.05 mg/kg twice daily.
Read the study38 boys with Duchenne muscular dystrophy on steroids (17 treated, 21 controls)
6-minute walk distance did not change; growth rate was 6.5 vs 3.3 cm a year.
Read the study12 obese adults with type 2 diabetes, 6 weeks
HbA1c fell from 10.4% to 8.1% at 100 mcg/kg twice daily; significant side effects occurred in some patients, and only 6 of 12 completed the full 6 weeks.
Read the studyNo preclinical studies are listed as key studies here. The human data above carries the evidence.
When a new Mecasermin study in people is published, the daily email covers it.
These are questions the published research has not answered.
The label limits use to severe primary IGF-1 deficiency (height and IGF-1 both at least 3 standard deviations below average, with normal or high growth hormone) and growth hormone gene deletion with neutralizing antibodies. It is not a substitute for growth hormone and is not for IGF-1 deficiency caused by growth hormone deficiency, malnutrition, low thyroid or steroid treatment. A second product, Iplex (mecasermin rinfabate, IGF-1 bound to IGFBP-3, Insmed), also appears on FDA's 2020 list of drugs deemed biologics. Increlex lost EU orphan status in August 2017 at the end of its 10-year exclusivity; the EU marketing authorization holder is Esteve. Prohibited at all times under WADA S2.3, which names mecasermin.
When the FDA or WADA changes Mecasermin's status, it's in the next morning's email.
How much of Mecasermin is left after a single dose
Simple first-order model from the published half-life. Real clearance varies with dose, route, kidney and liver function and formulation. This is not a dosing schedule.
This table records the doses that trials and approved labels used, with the source for each row. It is a record of research, not a recommendation, and it is open to free members.
Which symptoms are expected and which mean stop and get help: side effects and red flags.
Tap a claim to see what the studies found.
No trial has tested it for muscle growth in healthy people. In boys with Duchenne muscular dystrophy and in ALS, it did not improve muscle function.
Increlex is a licensed biologic made under FDA oversight. Research IGF-1 products, including IGF-1 LR3, are different molecules or unverified material.
The label limits it to severe primary IGF-1 deficiency and growth hormone gene deletion with antibodies. It is not for children with growth hormone deficiency.
Long-term treatment added a mean 13.4 cm, but most patients still finished below the normal adult range.
These pairings come up often. Almost none have been tested together in a trial, and the evidence note on each says so plainly.
Discussed online as a way to stack muscle-building signals.
EvidenceNo trial has tested this in healthy adults. Both drugs affect blood sugar in different directions, and WADA bans both. Any such use is outside the label.
Not supplied as a powder. Increlex comes as a 40 mg/4 mL solution in a multiple-dose vial: refrigerate at 2 to 8 C, protect from light, do not freeze (label).
No mixing needed. After first opening, keep refrigerated and use within 30 days (label).
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