What it is
Growth hormone is made by the pituitary, a pea-sized gland under the brain. In children it drives growth in height; in adults it helps regulate body fat, muscle, bone and blood sugar. Much of its effect runs through a second hormone, IGF-1, made mainly in the liver when growth hormone rises.
Somatropin is the lab-made version. It has exactly the same 191 building blocks as the natural hormone and is produced by bacteria or cultured cells carrying the human gene. It is a prescription medicine sold under several brand names and is injected under the skin, usually every day.
Three newer once-a-week products, Sogroya, Skytrofa and Ngenla, are related but chemically different molecules, described below only for comparison.
Somatropin is a non-glycosylated, single-chain 191-residue protein (22,124 Da per the Genotropin label) with a sequence identical to pituitary hGH. It binds the growth hormone receptor, a cytokine-family receptor that signals through JAK2 and STAT5, stimulating hepatic IGF-1 synthesis and exerting direct effects: lipolysis, nitrogen retention, sodium and phosphate retention, and reduced insulin sensitivity. It also inhibits 11β-HSD1, which can unmask central adrenal insufficiency.
Genotropin label pharmacokinetics in adults with GH deficiency: subcutaneous bioavailability about 80%, Tmax about 6 hours, apparent clearance 0.3 L/h/kg, volume 1.3 L/kg, terminal half-life 3.0 hours subcutaneously versus 0.4 hours intravenously, the difference reflecting slow absorption. Clearance is by proteolysis in liver and kidney.
The weekly products differ structurally: somapacitan carries an L101C substitution with an albumin-binding side chain; lonapegsomatropin is somatropin transiently linked to a 4 × 10 kDa methoxy-PEG carrier and releases unmodified somatropin; somatrogon fuses hGH to C-terminal peptides from the hCG β chain.
Who made it and when
From 1963 to 1985, American children short of growth hormone were treated with hormone extracted from the pituitary glands of people who had died, supplied by a government program. In 1985 three young men treated this way died of Creutzfeldt-Jakob disease, a fatal brain disease caused by infectious proteins, and distribution stopped at once. Of nearly 7,700 US recipients, 36 had developed the disease as of November 2020.
A lab-made replacement arrived the same year. Genentech had shown in 1979 that bacteria could make the hormone, and its product Protropin was approved in October 1985. Protropin carried one extra building block; Lilly’s Humatrope, approved in 1987, matched the natural hormone exactly. Several more brands followed through 2006.
The NIH-funded National Hormone and Pituitary Program distributed cadaveric pituitary hGH from 1963 to 1985. HHS halted distribution in 1985 after three recipients died of CJD; it has identified 36 cases among nearly 7,700 US recipients, none among patients who began treatment after 1977, when an additional purification step was introduced.
Goeddel et al. (Nature 1979) expressed a hybrid synthetic/cDNA hGH gene in E. coli. Genentech’s Protropin (somatrem, methionyl-hGH, 192 residues) was approved on 18 October 1985 as the company’s first product and ceased production in 2004. FDA’s 2020 list of deemed biologics licences gives initial approval dates for the somatropin applications: Humatrope 1987, Nutropin 1993, Zomacton 1995, Genotropin 1995, Serostim and Saizen 1996, Norditropin (current application) 2000 and Omnitrope 2006. Genentech discontinued all Nutropin AQ NuSpin formulations in the US on 31 December 2024 for business reasons. The weekly analogues followed: Sogroya (adults 2020, with pediatric indications added through February 2026), Skytrofa (children 2021, adults 2025) and Ngenla (children 2023).
What the data say
In the labelled conditions, trials reported increased growth in children and, in adults with a proven deficiency, less body fat and more lean mass. Outside those conditions the controlled evidence is thin.
A small 1990 study in older men reported more lean mass and less fat after six months. Growth hormone later became widely promoted as an “anti-aging” treatment, a use the FDA has never approved. Larger trials in older adults confirmed modest changes in body composition but little or no gain in strength, with frequent swelling, joint pain, carpal tunnel syndrome and new diabetes or high blood sugar. In recreational athletes, sprint capacity rose slightly and fell back after stopping. In very sick intensive-care patients, high doses roughly doubled the death rate.
Rudman et al. (NEJM 1990; 12 treated, 9 untreated men aged 61–81) reported lean body mass +8.8% and adipose mass −14.4% after 0.03 mg/kg three times weekly for six months. In the NIA trial (Blackman et al., JAMA 2002; n=131, 26 weeks), GH alone increased lean mass by 3.1 kg in men and 1.0 kg in women; strength did not rise significantly, edema affected 39% of women and arthralgia 41% of men on GH, and diabetes or glucose intolerance occurred in 18 GH-treated men versus 7. A systematic review of 18 study populations (220 GH-treated participants) found fat mass −2.1 kg and lean mass +2.1 kg with unchanged weight, more edema, arthralgia, carpal tunnel syndrome and gynaecomastia, and concluded that the evidence did not support GH as an anti-ageing therapy (Liu et al., 2007).
Meinhardt et al. (2010; n=96) found sprint capacity +3.9% after 2 mg/day for eight weeks, with no change in endurance, strength or power. Takala et al. (1999; n=532) reported in-hospital mortality of 39% versus 20% and 44% versus 18% in critically ill adults. FDA judged the French SAGhE mortality signal inconclusive in 2011.
Regulatory picture
Approval: somatropin is fully FDA approved, but only for what each brand’s label lists: growth failure in children from growth hormone deficiency and several genetic or birth-related conditions, growth hormone deficiency in adults, and, for Serostim, wasting in adults with HIV.
Compounding: since March 2020 somatropin has been regulated as a biological product, and pharmacies may not compound copies of it.
Distribution: unusually, federal law limits distribution outside the label. Since 1990 it has been a felony to distribute growth hormone, or hold it intending to distribute it, for any use other than an FDA-authorised one on a doctor’s order: up to five years in prison, or ten if a minor is involved.
Sport: the World Anti-Doping Agency prohibits growth hormone at all times.
Approval: each brand holds a biologics licence, deemed on 2020-03-23 under section 7002(e) of the BPCI Act. Labelled Genotropin regimens, as historical label facts: pediatric GH deficiency 0.16–0.24 mg/kg/week, Prader-Willi syndrome 0.24, Turner syndrome 0.33, idiopathic short stature up to 0.47 and small for gestational age up to 0.48 mg/kg/week, each divided into 6 or 7 subcutaneous injections; adult GH deficiency starting at no more than 0.04 mg/kg/week (maximum 0.08) or about 0.2 mg/day without weight adjustment, titrated to IGF-1.
Compounding: FDA’s March 2020 notice states that transitioning biological products are not eligible for the 503A and 503B exemptions, so the compounding field is recorded as restricted.
Distribution: 21 U.S.C. 333(e), in its 1990 form, covers somatrem, somatropin and analogues, treats convictions as Controlled Substances Act felonies for forfeiture purposes, and authorises DEA investigation. The 2007 systematic review above notes that distribution as an anti-ageing agent is illegal in the US.
Sport: WADA 2026 section S2.2.3 lists growth hormone and its analogues, naming lonapegsomatropin, somapacitan and somatrogon.
