What is somatropin?

What is somatropin?

Somatropin is human growth hormone made by bacteria. Scientists put the human gene for the hormone into Escherichia coli, a common lab bacterium. This is called recombinant DNA technology. The bacteria then build the hormone for us. The finished protein is a chain of 191 amino acids, the small building blocks that make up every protein. Its order of building blocks is identical to the growth hormone your own pituitary makes. The Humatrope label gives a weight of about 22,125 daltons. The Genotropin label gives 191 building blocks and 22,124 daltons. A dalton is a tiny unit used to weigh molecules.

Because the chain matches the natural hormone, somatropin is a copy of the hormone. It is not a signal that asks the body to release hormone.

That is the main difference from the other peptides in this hub. Those are different molecules, and they press different switches on different cells. The page on HGH and releasing peptides puts the groups side by side.

A chain of 191 building blocks is long for a hormone. Is it a peptide or a protein? The page on peptides and proteins explains the naming habit. Chain length alone is not a strict line between the two.

How does somatropin act in the body?

Somatropin works by docking onto a receiver on the outside of a cell. That receiver is called the growth hormone receptor. It is "dimeric", which means it works as a pair. According to the Humatrope label, docking sends a message into the cell. The cell then reads certain genes and builds new proteins from them. The label names three: IGF-1, IGF binding protein-3 and the acid-labile subunit. IGF-1 means insulin-like growth factor 1. It is a second hormone that carries part of the growth hormone message onward. So growth hormone often works through a relay, not only directly.

The label says somatropin has direct effects on tissues and on how the body handles fuel. It also has indirect effects that pass through IGF-1. The label lists effects on growth plates, on how much sugar the liver releases, on how the body builds protein and on how it breaks down fat. This page repeats the label's account of how the hormone works. It does not repeat the details of approved use.

The label does not describe the steps between the receiver and the new proteins. A 2010 review in Nature Reviews Endocrinology fills in that picture. It describes the receptor as a pair that already exists before the hormone arrives. When the hormone docks, the two halves shift position. That shift switches on JAK2, an enzyme attached to the inside of the receptor. An enzyme is a protein that speeds up a chemical step. JAK2 then tags the receptor and other proteins with phosphate groups, which works like flipping them to "on".

A 1992 study in Science took a 3D snapshot of the hormone stuck to the outer part of its receptor. It showed one hormone molecule holding two receptor molecules, like one hand gripping two handles. This was a picture of purified proteins in the lab, not of a living body.

What is somatropin approved for?

The Humatrope label, approved by the FDA, lists uses in children and in adults. In children it lists poor growth because the body makes too little growth hormone. It also lists short height linked to Turner syndrome, short height with no known cause (idiopathic short stature), SHOX deficiency, and short height in children born small for their stage of pregnancy. In adults it lists replacing growth hormone when the body lacks it. These are named uses of a prescription medicine, and each one is tied to a diagnosis. The approval covers somatropin products only. It is not an approval of any releasing peptide.

The Genotropin label splits adults who lack growth hormone into two groups. In the first group the problem started in adulthood. It came from disease of the pituitary or the hypothalamus, a nearby control area of the brain, or from surgery, radiation or injury. In the second group the problem started in childhood.

The Genotropin label also notes how doctors usually confirm the diagnosis in adults. They generally use a growth hormone provocative test. That is a clinical test that checks how the pituitary responds when it is challenged.

What do the Australian and sport records say about somatropin?

In Australia, somatropin has its own Schedule 4 entry, and Appendix D clause 5 applies. Schedule 4 is the prescription-only group. This comes from the October 2026 Poisons Standard, instrument F2026L01327, checked line by line on 16 October 2026. The national medicines database, the Australian Register of Therapeutic Goods (ARTG), lists one somatropin medicine, Genotropin, ARTG 78811, in the same check. In sport, the WADA 2026 Prohibited List names growth hormone, its analogues and fragments at S2.2.3. The list has applied since 1 January 2026, and it bans these substances at all times.

A registered product is approved only for the uses and form written on its own entry. One ARTG listing for one product does not approve every product with the same ingredient.

What Schedule 4 and Appendix D mean explains both Poisons Standard terms. The legal status page lists the matching rows for the releasing peptides.

Evidence limits

What do the label and records not tell a reader about somatropin?

That is why the hub keeps the three groups apart. The label supports statements about somatropin, and only somatropin.

The pages on CJC-1295 and ipamorelin report what studies of those compounds measured. Their results are not somatropin results.