Mecasermin: evidence, FDA status and research

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Mecasermin is pharmaceutical IGF-1, and in bodybuilding circles it is treated as a muscle-building hormone, even though its only approved use is to make very short children grow.

Studies say

Uncontrolled follow-up of 76 children with IGF-1 deficiency showed growth velocity roughly tripling in the first year, enough for approval in a rare disease but not for an A, and there are no trials for any other use.

Why grade B. The approval rests on open-label, uncontrolled studies: the cited 2007 report followed 76 children with severe primary IGF-1 deficiency for up to 12 years, using each child's pre-treatment growth rate as the comparison. No placebo-controlled trial exists, which is defensible for a rare pediatric disease but keeps the grade at B. The off-label uses promoted online (muscle growth, recovery) have no human trials at all. ¹²

FDA. Approved. Mecasermin (Increlex) was approved in 2005 for growth failure in children with severe primary IGF-1 deficiency, or with growth hormone gene deletion who have developed neutralizing antibodies to growth hormone. It is not approved for any adult use or for muscle building. ²

Written from 2 cited sources. Fact-checked 2026-10-27: 14 claims checked, 4 corrected. Last refreshed 2026-10-27. Not physician reviewed.

Evidence checklist

Randomised controlled trial Open-label, uncontrolled studiesno
Human study over 100 people 76 children followed up to 12 yearsyes
More than one research group Mostly sponsor-run registration studiesno information
Clinical outcomes, not surrogate markers Height velocity in childrenyes
Human safety data beyond case reports Hypoglycemia rates from label datayes

Drawn from the cited studies below. A dash means the sources give no information.

What it is

Mecasermin is recombinant human insulin-like growth factor 1 (IGF-1), a 70-amino-acid protein identical to the one the liver makes in response to growth hormone. IGF-1 is the hormone that actually drives most childhood bone growth; growth hormone works largely by raising it. Children whose bodies cannot make IGF-1 despite normal or high growth hormone (Laron syndrome and related conditions) do not respond to growth hormone therapy, and mecasermin was developed to replace the missing hormone directly. ¹²

It was approved in 2005 and is sold as Increlex, now made by Eton Pharmaceuticals in the US. The label limits it to children 2 years and older with severe primary IGF-1 deficiency, defined by very short height, very low IGF-1, and normal or high growth hormone, and to children with growth hormone gene deletions who have made antibodies against injected growth hormone. ²

How it works

IGF-1 binds the IGF-1 receptor on growth plate cartilage, muscle, and many other tissues, triggering cell division and protein synthesis. In the growth plate that lengthens bone. Because IGF-1 is structurally related to insulin and binds the insulin receptor weakly, it also lowers blood glucose, which is why hypoglycemia is the main acute side effect and why the drug is given shortly after a meal. ²

What human research shows

The cited 2007 study pooled 76 children with severe primary IGF-1 deficiency treated with mecasermin for up to 12 years. Height velocity rose from an average of 2.8 cm per year before treatment to 8.0 cm per year in the first year, then declined in later years while remaining above baseline for up to 8 years. Final adult heights improved compared with untreated historical patients but stayed well below population norms. ¹

No randomized comparison exists, and no trials have tested mecasermin for muscle growth, athletic performance, or any adult indication. Observations from the pediatric population cannot be transferred to those uses. ¹²

Study	Model	Finding
Long-term mecasermin in severe primary IGF-1 deficiency (Chernausek 2007)	Humans, n=76 children, open-label uncontrolled, up to 12 years	Height velocity rose from 2.8 to 8.0 cm per year in year one and stayed above baseline; hypoglycemia was the main side effect. ¹
Increlex prescribing information	FDA label	Approved for severe primary IGF-1 deficiency and GH gene deletion with neutralizing antibodies; warnings for hypoglycemia, tonsillar hypertrophy, intracranial hypertension, and malignancy. ²

Safety

Hypoglycemia is the most common adverse effect, reported in about half of children in the registration studies, with a few experiencing seizures. The label also lists enlarged tonsils and adenoids (which can cause snoring and sleep apnea), intracranial hypertension, fat accumulation at injection sites, progression of scoliosis, and slipped capital femoral epiphysis, a hip problem of fast-growing children. ¹²

Because IGF-1 drives cell growth, the label contraindicates it in children with cancer or a history of cancer. Whether long-term IGF-1 exposure raises cancer risk later in life is unknown; the treated population is small and follow-up is limited. Adults using it off-label have no safety data to draw on. ²

Questions for your clinician

Is mecasermin approved for muscle building or any adult use?
How is low blood sugar managed with each dose?
How are tonsil size and hearing checked during treatment?

Questions people ask

Which children is mecasermin meant for?

Growth failure in children whose bodies cannot make IGF-1 despite normal growth hormone, and in children with growth hormone gene deletion who have antibodies to growth hormone. Those are the only approved uses. ²

How is it different from growth hormone?

Growth hormone works mainly by telling the liver to make IGF-1. Mecasermin is IGF-1 itself, so it works in children whose problem is downstream of growth hormone. ¹²

Does mecasermin build muscle in adults?

There are no human trials of mecasermin for muscle growth or performance. The only published efficacy data come from children with a rare deficiency. ¹

What hazards come with treatment?

Low blood sugar is the main one, affecting about half of treated children. Enlarged tonsils, raised pressure in the skull, hip problems, and a theoretical cancer risk are also on the label. ¹²

Citations

Chernausek 2007, J Clin Endocrinol Metab: Long-term treatment with recombinant IGF-1 in children with severe IGF-1 deficiency doi.org
FDA 2025: Increlex (mecasermin) prescribing information accessdata.fda.gov