Human growth hormone (HGH), also known as somatotropin, is a peptide hormone produced by the anterior pituitary gland located in the brain. It plays a crucial role in growth, cell regeneration, and cell reproduction in humans. HGH stimulates growth and development in children and adolescents and has important effects on various aspects of metabolism and body composition in adults.

The main functions of human growth hormone include:

1. Growth promotion: HGH stimulates the growth of bones and cartilage, primarily through the production of insulin-like growth factor 1 (IGF-1) in the liver. IGF-1, in turn, promotes cell growth and division, leading to increased bone length and thickness, as well as overall body growth.
2. Muscle growth and maintenance: HGH helps to increase muscle mass by stimulating protein synthesis and promoting the differentiation and proliferation of muscle cells. It also plays a role in muscle maintenance and repair by supporting the regeneration of muscle fibers.
3. Fat metabolism: HGH promotes lipolysis, the breakdown of fat stored in adipose tissue. This process releases fatty acids into the bloodstream, which can be used as an energy source by the body. HGH also helps to reduce the accumulation of fat by inhibiting its synthesis.
4. Carbohydrate metabolism: HGH has complex effects on carbohydrate metabolism, including promoting glucose production in the liver (gluconeogenesis) and reducing the sensitivity of peripheral tissues to insulin. These effects help to maintain blood glucose levels during periods of fasting or stress.
5. Cell regeneration and repair: HGH supports the regeneration of various tissues in the body, including skin, bones, and muscles, by promoting cell growth and division.

HGH levels naturally decline with age, which can contribute to changes in body composition, bone density, and muscle mass. In some cases, individuals may have a deficiency in growth hormone production, which can lead to growth disorders in children (e.g., short stature) or a condition called adult growth hormone deficiency in adults, characterized by reduced muscle mass, increased body fat, and decreased bone density.

Synthetic HGH is available as a prescription medication for the treatment of growth hormone deficiency and other medical conditions. However, the use of HGH for performance enhancement or anti-aging purposes is not approved by regulatory authorities and may be associated with various health risks and side effects.