Overview
Following subcutaneous injection, rhGH is absorbed with a bioavailability of approximately 75–80%, reaching peak serum concentrations (Cmax) within 2–4 hours. It is cleared primarily through hepatic and renal metabolism with a plasma half-life of 3–5 hours. IGF-1 levels rise with a delay of 8–24 hours post-injection and remain elevated for 12–18 hours, providing the sustained anabolic window. Chronic administration upregulates hepatic GHR density and increases basal IGF-1 substantially — clinical studies show IGF-1 increases of 30–60% from baseline at doses of 2–4 IU/day. GH also stimulates thyroid hormone metabolism, increasing T4-to-T3 conversion demands through deiodinase activity, potentially precipitating subclinical hypothyroidism.
Proposed mechanism
HGH binds to the GH receptor (GHR), a class I cytokine receptor, triggering JAK2-STAT5 signaling pathways that stimulate transcription of insulin-like growth factor 1 (IGF-1) primarily in the liver. IGF-1 then mediates most of the anabolic effects of GH — including protein synthesis, cellular proliferation, and longitudinal bone growth — while GH itself directly promotes lipolysis in adipose tissue via hormone-sensitive lipase activation. GH also antagonizes insulin signaling, increasing hepatic glucose output and promoting free fatty acid mobilization.
What the evidence supports
Randomised controlled trial data in humans exists and supports use in specific contexts.
Graded Clinical
Findings supported by randomised, controlled trials in humans, with pre-registered endpoints and published results.
Key citations
Representative primary sources, including results that did not favour the compound.
- [1]
Growth hormone and the insulin-like growth factor system in myogenesis
· Endocrine Reviews (doi:10.1210/er.2009-0024) · 2010
- [2]
Consensus guidelines for the diagnosis and treatment of adults with GH deficiency II (2007 revision)
· European Journal of Endocrinology (doi:10.1530/EJE-07-0631) · 2007
- [3]
Effects of growth hormone on glucose metabolism and insulin resistance in human
· Annals of Pediatric Endocrinology & Metabolism (doi:10.6065/apem.2019.24.2.92) · 2019
- [4]
Cancer risk following growth hormone use in childhood: implications for current practice
· Drug Safety (doi:10.2165/11632080-000000000-00000) · 2012
- [5]
GH replacement in hypopituitary adults: long-term effects on body composition — evidence from the KIMS database
· European Journal of Endocrinology (doi:10.1530/EJE-13-0286) · 2013
Citation records in this build are illustrative placeholders for the design.
Reference information for research purposes. Not medical advice, and not a recommendation to use any compound. Many entries describe substances that are not approved for human use.