Most compounds in this category ask the pituitary to release growth hormone. Somatropin is the hormone, made to the exact human sequence.
HGH 191AA · Recombinant human growth hormone
Growth hormone is a protein released by the pituitary gland in pulses, mostly during sleep. It acts directly on tissues and also prompts the liver to make IGF-1, a second hormone that carries much of the growth signal. Researchers study it because it sits at the centre of growth, body composition and metabolism across the lifespan. It has one of the largest clinical literatures of any compound in this catalogue, in defined medical conditions.
Human growth hormone is a 191-amino-acid protein produced by the anterior pituitary. Somatropin is the recombinant form: the same sequence, produced in engineered cells rather than extracted from tissue. “191AA” in the product name signals that exact-sequence form, as distinct from an early recombinant version that carried an extra methionine (192 amino acids) and was more likely to provoke antibodies (Ayyar, 2011).
The number describes the main form, not the only one. The pituitary also secretes smaller natural variants, including a 20 kDa isoform produced by alternative splicing of the same gene (Baumann, 2009). Growth hormone acts through its own receptor on many cell types — muscle, bone, fat, liver — and one of its effects in the liver is to increase production of IGF-1 (insulin-like growth factor 1). Both direct actions and IGF-1-mediated actions contribute to its biology; the “somatomedin hypothesis” that IGF-1 explains everything has been revised as evidence for direct effects accumulated (Le Roith et al., 2001).
The clinical history runs from pituitary-extracted hormone in the 1950s, halted in 1985 after cases of Creutzfeldt–Jakob disease were traced to contaminated extracts, to recombinant somatropin from 1985 onward (Ayyar, 2011). Decades of randomised trials in children with growth hormone deficiency and other growth disorders, and in adults with confirmed deficiency, underpin its registered uses. A review by Ranke and Wit summarises that literature and the open questions (Ranke and Wit, 2018).
Because pituitary release is pulsatile and hard to sample, research usually measures IGF-1 as a steadier proxy. That is a practical choice, not a statement that IGF-1 is the whole mechanism. Research in people without deficiency — ageing, body composition, athletic performance — is a separate and more contested literature, in which effects on lean mass have generally not translated into measured functional gains, and adverse effects such as fluid retention and joint pain are consistently reported.
The well-established evidence is for registered indications in patients with confirmed deficiency or defined growth disorders, using registered medicines with known potency and sterility. It does not describe the material supplied here, which is a research reagent. Recombinant proteins are sensitive to handling and vary between manufacturers in potency and impurity profile, which is why batch documentation matters more for a protein than for a small synthetic peptide. Growth hormone is prohibited at all times in sport under WADA category S2.
Somatropin is a Schedule 4 (prescription-only) medicine in Australia, registered for defined growth hormone deficiency and growth disorders. The material supplied here is a research reagent, not a registered medicine. Growth hormone is prohibited at all times in sport under WADA category S2.
Sources and status checked 2026-09-22
HGH 191AA — sizes and pricing