Key takeaways
- Human growth hormone (HGH, or somatropin) is a hormone the pituitary makes naturally. The recombinant form replaces what is missing in people with a diagnosed growth hormone deficiency.
- It acts on tissues directly and through liver-produced insulin-like growth factor 1 (IGF-1), shaping muscle, bone, and fat metabolism.
- The strongest evidence is in adults and children with confirmed deficiency, identified through endocrine stimulation testing rather than symptoms or age alone.
- A 2020 phase 3 randomized controlled trial and a more recent phase 3 trial in adults both support modern once-weekly long-acting replacement, alongside an established record for daily somatropin.
- Recombinant growth hormone (Genotropin and similar products) is FDA approved for growth hormone deficiency in both children and adults, which is the population the research centers on.
What is growth hormone?
Human growth hormone (HGH, also called somatropin or somatotropin) is a hormone produced naturally by the pituitary gland at the base of the brain. In childhood it drives normal growth, and throughout life it helps regulate body composition, metabolism, bone strength, and how the body uses fats, proteins, and carbohydrates. Levels are highest in youth and decline gradually with age, which is a normal part of human physiology rather than a disease in itself.
The therapeutic form, recombinant human growth hormone, is identical to the hormone the body makes. It is used to replace what is missing in people who have a diagnosed growth hormone deficiency. That replacement model is what the established research is built around.
How it works
The pituitary releases growth hormone in pulses. It acts directly on tissues and indirectly by prompting the liver to produce insulin-like growth factor 1 (IGF-1), and together these signals influence muscle and bone, fat metabolism, and tissue maintenance. When the pituitary does not make enough, this cascade is blunted, which can affect body composition, energy, bone density, and metabolic health in adults.
Replacement restores growth hormone toward normal physiological levels in people who are genuinely deficient. Like other hormone replacement, the goal is to correct a measured shortfall, not to push levels above normal. That distinction is central to using HGH safely and appropriately.
What the evidence supports in diagnosed deficiency
The strongest and most established evidence for HGH concerns adults and children with diagnosed growth hormone deficiency. A 2021 review in Reviews in Endocrine and Metabolic Disorders outlines current concepts for diagnosing adult growth hormone deficiency, describing how growth hormone stimulation testing identifies an appropriate candidate. That review also catalogs what untreated deficiency looks like in adults: increased visceral fat, reduced lean mass and bone density, unfavorable lipids, and impaired quality of life. A companion 2021 review in the same journal examined deficiency and replacement therapy in adults, including its impact on survival, and reported that modern replacement brings mortality in this population close to that of the general population. Accurate diagnosis is the foundation the rest of the evidence rests on.
The interventional evidence comes from phase 3 trials of long-acting replacement. A 2020 phase 3 randomized controlled trial published in the Journal of Clinical Endocrinology and Metabolism evaluated once-weekly somapacitan, a long-acting form of growth hormone, in adults with growth hormone deficiency. It significantly reduced truncal fat and improved visceral fat and lean body mass versus placebo, with a safety profile in line with daily growth hormone. A more recent phase 3 trial, foresiGHt (NCT04615273), compared once-weekly lonapegsomatropin against both placebo and a daily somatropin product in 264 adults with growth hormone deficiency, using change in trunk fat as its primary measure. Together these trials, the highest tier of clinical evidence, support both daily and modern once-weekly replacement in this diagnosed population.
This is also a compound with a long approved track record. Recombinant somatropin (for example Genotropin) is FDA approved for growth hormone deficiency in adults and in children, and for several pediatric growth-failure conditions such as Turner syndrome and being born small for gestational age. The approved use and the clinical evidence point to the same place: HGH is for correcting a diagnosed deficiency. The research does not establish a benefit for healthy adults using it simply to slow aging, build muscle, or boost performance, and that is where the current evidence stops.
Who it may suit
HGH replacement is intended for people with a confirmed growth hormone deficiency, defined by diagnosis rather than symptoms or age. Whether it is relevant for a given person is a clinical decision that belongs with a licensed physician who can review the full picture, including bloodwork and medical history. We do not provide dosing or administration guidance, and this article does not replace that evaluation.
The evidence
Selected references, each verified against primary sources (PubMed, ClinicalTrials.gov, and the FDA label). Explore the full, filterable research library on our Science page.
This article is for educational purposes only and is not medical advice, a diagnosis, or a treatment recommendation. Growth Hormone (HGH) is discussed in the context of the published research; inclusion of a study does not imply a guaranteed outcome. Many of these compounds are investigational and not approved for the uses described in all jurisdictions. Any treatment decision should be made with a qualified physician. Individual results vary.