What it is
Somatropin is recombinant human growth hormone, made by recombinant DNA technology. The FDA label for one somatropin product describes a protein of 191 amino acids whose sequence is identical to that of human growth hormone of pituitary origin. It is FDA-approved for several specific conditions: in children, growth failure due to growth hormone deficiency, Prader-Willi syndrome, being born small for gestational age, Turner syndrome and idiopathic short stature, and in adults, growth hormone deficiency.
It is the reference point that growth hormone secretagogues and GHRH analogs are compared against, because it supplies growth hormone directly rather than stimulating its release. In the US, distributing it for non-approved uses is a federal offense, and it is prohibited by the World Anti-Doping Agency (WADA).
How it's thought to work
Somatropin binds growth hormone receptors directly, stimulating liver production of IGF-1, fat breakdown (lipolysis), protein synthesis and cellular growth. Unlike secretagogues, it bypasses pituitary regulation entirely, so natural feedback control does not limit exposure. The FDA label states that in children it stimulates linear growth and in patients with growth hormone deficiency normalizes IGF-1 concentrations, and that in adults with deficiency it results in reduced fat mass and increased lean body mass.
What the research says
Somatropin has decades of clinical use: the product whose label is cited here has had US approval since 1987, and the label summarizes clinical studies in adult growth hormone deficiency, Prader-Willi syndrome, small for gestational age, Turner syndrome and idiopathic short stature. It is FDA-approved for those conditions only.
Reported side effects
The FDA label describes fluid retention in adults (edema, joint pain, muscle pain and nerve compression syndromes including carpal tunnel syndrome), usually transient. It also warns that impaired glucose tolerance and diabetes mellitus may be unmasked during treatment, that new-onset type 2 diabetes has been reported, and that long-term overdosage could produce signs of gigantism or acromegaly, meaning excess growth of soft tissue and bone.
Reconstitution
Somatropin is supplied as a lyophilized (freeze-dried) powder in vials or pen cartridges whose strength is labeled in international units (IU) as well as milligrams; the PeptidesAI encyclopedia lists 10 IU (about 3.3 mg) vials and 36 IU (about 12 mg) pen cartridges.
Worked example. A 3.33 mg vial is 3,330 mcg. Reconstituted with 1 mL of BAC water, that works out to 3,330 mcg ÷ 1 mL = 3,330 mcg/mL. On a U-100 insulin syringe, where each unit is 0.01 mL, each unit holds 3,330 × 0.01 = 33.3 mcg. Use the peptide reconstitution calculator to work out the concentration and units for any vial size and water volume.
Important notes
Somatropin is FDA-approved for specific indications only. In the US, distribution for non-approved uses, including anti-aging or athletic use, is a federal offense, and it is prohibited by WADA. The label states that therapy is to be supervised by a physician experienced in the diagnosis and management of the conditions it treats, and it lists contraindications including acute critical illness and active malignancy.
Sources
- GENOTROPIN (somatropin) for injection, for subcutaneous use - Prescribing Information. U.S. Food and Drug Administration, 2025. Fda label
Frequently asked questions
These questions cover the same ground as the sections above, in a shorter format.
What is somatropin?
Recombinant human growth hormone (191 amino acids), identical in sequence to the pituitary hormone and FDA-approved for growth hormone deficiency and several other specific conditions.
How is somatropin thought to work?
It binds growth hormone receptors directly, stimulating IGF-1 production, fat breakdown, protein synthesis and growth, and it bypasses the pituitary's own regulation.
What does the research on somatropin say?
It has decades of clinical use, and the FDA label summarizes studies in children and adults for its approved conditions only.
What are the reported side effects of somatropin?
Fluid retention, joint and muscle pain, carpal tunnel symptoms, glucose intolerance, and with long-term excess, acromegaly-type changes.
How much is one unit from a 3.33 mg Somatropin (HGH) vial?
With 1 mL of BAC water, a 3.33 mg vial is 3,330 mcg/mL, so one unit on a U-100 syringe (0.01 mL) holds 33.3 mcg.
The full entry, plus the calculator
The PeptidesAI app has the complete encyclopedia entry for Somatropin (HGH) — one of 70 compounds covered — plus the reconstitution calculator, a dose log and reminders. Free to download on iPhone.
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