Mecasermin

Mechanism and glucose effects

Mecasermin supplies human insulin-like growth factor 1, or IGF-1. This protein helps bones and other tissues grow. It also lowers blood glucose, which makes food intake and glucose monitoring central to treatment.⁴⁶⁶

Who Increlex is for

The US label covers children aged 2 and older with severe primary IGF-1 deficiency, or a growth-hormone gene deletion with neutralizing antibodies to growth hormone. Diagnosis combines marked short stature, very low IGF-1 and normal or elevated growth hormone.⁴⁶⁶

Finding the cause of low IGF-1

Low IGF-1 can also result from poor nutrition, hypothyroidism, growth-hormone deficiency or corticosteroid treatment. These conditions require assessment of the underlying cause and fall outside the Increlex indication.⁴⁶⁶

Name	What it refers to
Mecasermin	Recombinant human IGF-1 with the native 70-amino-acid sequence. Increlex is a prescription product containing it.
Mecasermin rinfabate	IGF-1 combined with IGF-binding protein 3. It has a separate product history and study program.
Growth hormone	A different hormone that normally stimulates IGF-1 production.

How much did growth improve?

The first year produced the largest increase in growth rate.

2.8 to 8.0 cm/year

Mean growth velocity rose from 2.8 cm/year before treatment to 8.0 in the first year. Later annual means were lower: 5.8 in year two and 4.3 in year eight. The number with measurements fell from 58 to 13 across those years.⁴⁶⁶

Growth measurements

The US program pooled five studies, mostly open label. Children had severe IGF-1 deficiency and received treatment under specialist care. Growth velocity records how quickly a child grows during a year; final height requires follow-up through the end of growth.⁴⁶⁶

13.4 cm above historical expectations

Twenty-one children were treated continuously for an average of 10 years. Their final or near-final height averaged 13.4 cm above the height predicted from historical untreated Laron-syndrome data. Three reached the normal adult-height range; nine also received a GnRH analogue to delay puberty.⁴⁶⁸

How to read the long-term result

The adult-height paper followed a selected group from the larger treatment program and used historical controls. The European label and Study 1419 registry report overlapping patients.^468,469,470

A newer near-adult follow-up

An observational analysis of the Global IGFD Registry included 102 patients who reached near-adult height. Their mean height standard-deviation score improved by 0.9 during treatment, which lasted a median of 3.9 years. Treatment had begun at a mean age of 11.8 years.⁴⁷⁹

What needs monitoring?

Low blood sugar is the main immediate risk.

30 children had hypoglycemia

Five children had severe episodes needing help, and four had seizures or loss of consciousness. Fourteen of the 30 already had a history of low blood sugar. The label links treatment to food intake and glucose checks, especially when treatment starts.⁴⁶⁶

Headaches and vision changes

Intracranial hypertension occurred in three children in the US safety group. The label calls for eye examinations before treatment and during follow-up. Headache, nausea, vomiting and visual symptoms warrant assessment.⁴⁶⁶

Tonsils, breathing and rapid growth

Enlarged tonsils occurred in 11 of the 71 children, and seven had surgery. Monitoring also covers snoring, sleep apnea, scoliosis and hip problems during rapid growth. FDA expanded the hip warning in July 2025 to include osteonecrosis with slipped capital femoral epiphysis; a new limp or hip or knee pain needs assessment.^466,471

Cancer warnings

The current US label contraindicates Increlex in children with malignant neoplasia or a history of malignancy. Malignant tumors have been reported after treatment; whether mecasermin caused them is unknown. The UK safety review found cases during authorized use as well as off-label or excessive use.^466,472

Pregnancy and breastfeeding

The US label has no available human pregnancy data and no information on mecasermin in human milk, effects on a breastfed infant or milk production.⁴⁶⁶

The medicine and the label

Increlex is an approved prescription medicine. Its label varies by country.

Jurisdiction	Label scope
United States	Age 2 and older: severe primary IGF-1 deficiency, or GH-gene deletion with neutralizing GH antibodies.
European Union	Ages 2 to 18: severe primary IGF-1 deficiency, using the EU diagnostic criteria.
Canada	Ages 2 to 18: severe primary IGF-1 deficiency. The current monograph was revised in May 2026.

A small pharmacokinetic study

The often-quoted 5.8-hour half-life came from three children with severe primary IGF-1 deficiency after a single subcutaneous dose. Their responses varied substantially.^466,473

Growing after the growth plates close

Increlex is contraindicated for growth treatment after the growth plates have closed. The long-term height studies began treatment in childhood, while growth was still possible.^466,468

Compounding in the United States

FDA identifies Increlex as a licensed biological product. Its current compounding guidance says biological products are ineligible for the exemptions under sections 503A and 503B. Separate FDA guidance addresses mixing, dilution and repackaging of licensed biologics.^474,475,476

Competitive sport

The 2026 WADA list prohibits IGF-1, including mecasermin, and its analogues at all times under S2.3. The published 2027 list retains that classification.^477,478

Research beyond childhood growth

Native IGF-1 has also been studied in adults and in rare neurological conditions.

Body composition

A four-week randomized study assigned 16 healthy elderly women to growth hormone or one of two native IGF-1 doses. Lean mass and nitrogen retention increased in the higher-dose IGF-1 group, alongside headaches, lethargy, joint symptoms and bloating. The trial had no placebo group.⁴⁸⁰

Rett syndrome

A placebo-controlled crossover trial enrolled 30 girls with Rett syndrome. Mecasermin produced no significant improvement on its primary measures; some symptom and EEG measures worsened. Twelve serious adverse-event episodes occurred during the study.⁴⁸¹

ALS

A Cochrane review included three randomized trials with 779 participants. One trial favored IGF-1 on a functional score; the European trial and a later 330-person trial found no significant benefit on their primary measures. All three had high risk of bias, and survival benefit was unproven.⁴⁸²

Research and treatment in other countries

Japan has a distinct mecasermin product and a broader set of indications.

Japan: Somazon

The Japanese Somazon label covers selected insulin-receptor disorders as well as growth failure in certain growth-hormone-resistant conditions. It summarizes clinical experience in 12 people with insulin-receptor abnormalities and three with growth-hormone-resistant growth disorders.⁴⁸³

China: national clinical guidance

China's 2025 rare-disease guideline describes recombinant IGF-1 as a treatment for severe primary IGF-1 deficiency. The guideline discusses the treatment class; a current Chinese product authorization was not verified for this chapter.⁴⁸⁴

Russia: two children with Donohue syndrome

A 2026 report from the NMRC Endocrinology Center describes improved weight or growth in two children receiving mecasermin with nutritional and supportive care. Cardiomyopathy persisted in one child. The account was published by the treating institution and had no comparison group.⁴⁸⁵

Common questions

Growth results, side effects, cost and practical questions.

01 What is mecasermin, and who is Increlex for?

Mecasermin is recombinant human IGF-1. In the US, Increlex is labeled for growth failure in children age 2 or older with severe primary IGF-1 deficiency, or a GH-gene deletion with neutralizing GH antibodies. Diagnosis also includes growth measurements and growth-hormone testing.^466,486

02 How is Increlex given?

The US label describes Increlex as a 10 mg/mL solution injected under the skin, with the dose individualized by the specialist and tied to food because of low blood sugar risk.⁴⁶⁶

03 How much does Increlex cost, and does insurance cover it?

Current cash prices and insurer rules require current pharmacy and plan records beyond this page. The pharmacy and insurer can give the case-specific amount and coverage criteria.

04 Is mecasermin the same as IGF-1 LR3 or rinfabate?

No. Increlex contains native-sequence recombinant human IGF-1. Mecasermin rinfabate is a complex of IGF-1 and IGF-binding protein-3, while products sold as IGF-1 LR3 are separate from both.^466,486,467

05 Is Increlex used for bodybuilding or muscle gain?

Increlex is not approved for bodybuilding or muscle gain. A four-week study in 16 healthy elderly women found increased lean mass in the higher-dose native rhIGF-I group, but it had no placebo arm and did not test bodybuilding or athletic performance.^466,480

06 What side effects can Increlex cause?

Low blood sugar is the main immediate risk. The label also covers intracranial hypertension, enlarged tonsils or adenoids and sleep apnea, slipped capital femoral epiphysis, scoliosis progression, injection-site changes, hypersensitivity and neoplasia monitoring.^466,487,472

07 How much height did children gain?

In the US label's 58-child paired set, mean growth velocity rose from 2.8 to 8.0 cm/year in year one. Later annual means were lower, and the contributing group shrank to 13 by year eight. In 21 continuous-treated patients followed from childhood, mean height was 13.4 cm above historical untreated expectation after about 10 years; only three reached the normal range and nine also received a GnRH analog.^466,488,468

08 How does mecasermin work, and what does its half-life mean?

IGF-1 receptor signaling supports growth and also lowers glucose by increasing peripheral uptake and reducing liver output. In three children with severe primary IGF-1 deficiency, the label reports an apparent terminal half-life of 5.8 hours after one specified subcutaneous exposure.⁴⁶⁶

09 Is Increlex FDA approved?

Yes. FDA records show original US approval of Increlex in 2005, and the current label remains for the narrow pediatric indications described above.^474,489,466

10 Can adults or people with closed growth plates grow taller with it?

No verified study here shows height gain after growth plates have closed, and the US label lists closed epiphyses as a contraindication for growth treatment. The 21 near-adult patients had started treatment in childhood and were followed for about 10 years.^466,468

11 Is Increlex the same as HGH?

No. Growth hormone is upstream and normally stimulates IGF-1 production; mecasermin supplies IGF-1 activity directly. The US label says Increlex is not a substitute for growth hormone.⁴⁶⁶

12 How serious is low blood sugar with Increlex?

In the US label safety set, 30 of 71 children reported low blood sugar; five had severe episodes and four had a seizure or loss of consciousness. The label ties dosing to food and glucose monitoring, especially when treatment begins.⁴⁶⁶

13 How should Increlex be stored?

The US label says unopened and opened Increlex vials are refrigerated at 2 to 8 C, protected from direct light and not frozen. It says opened vials are discarded after 30 days.⁴⁶⁶

14 What if a child cannot eat or a dose is missed?

The US label says a dose is withheld when the child cannot eat shortly before or after it, and a later dose is not increased to make up for one that was omitted. Families should use the exact product instructions and the treating team's plan.⁴⁶⁶

15 Does mecasermin cause cancer?

In the US, Increlex is contraindicated in children with malignant neoplasia or a history of malignancy. Malignant tumors have been reported after treatment, but the current US label says the relationship to mecasermin is unknown; UK regulators note that cases also occurred within authorized use.^466,472