Somatropin (Recombinant Human Growth Hormone – HGH)

What is Somatropin?

Growth hormone (GH) is a protein hormone made by the pituitary gland at the base of the brain. It drives growth in childhood and helps control body composition, metabolism, bone strength and muscle throughout life.

Before 1985, children with growth hormone deficiency were treated with GH taken from the pituitary glands of deceased donors. That supply was withdrawn after it was linked to cases of Creutzfeldt-Jakob disease, a fatal brain infection. The same year, the first growth hormone made using recombinant DNA technology was approved. Today, all somatropin is made this way, by inserting the human GH gene into bacteria or other cells, which then produce pure hormone. It carries no risk of infection from human tissue.

Somatropin is a peptide hormone, not a steroid. It must be injected, because stomach acid and enzymes would destroy it if swallowed.

Long-acting growth hormone

Newer long-acting growth hormone products are injected once a week instead of daily, such as somapacitan (Sogroya), lonapegsomatropin (Skytrofa) and somatrogon (Ngenla). These are modified forms of growth hormone. They are not the same molecule as somatropin, but they treat similar conditions and may suit people who struggle with daily injections.

How does Somatropin work?

Growth hormone works in two ways: directly on tissues, and indirectly by making the liver produce a second hormone called IGF-1 (insulin-like growth factor 1).

1. Somatropin is injected and absorbed into the bloodstream.
2. It binds to growth hormone receptors on cells in the liver, bone, muscle and fat.
3. In the liver, this triggers the release of IGF-1, which carries much of GH's growth effect around the body.
4. In children, IGF-1 and GH act on the growth plates at the ends of long bones, making them lengthen.
5. In muscle, they increase protein building; in fat tissue, GH directly increases fat breakdown.
6. GH also raises blood sugar slightly by making the body less sensitive to insulin.

What changes can be expected?

In children: growth speed usually increases noticeably in the first year, often doubling in children with true growth hormone deficiency. Over years of treatment, many children reach an adult height close to their genetic target.

In adults with GH deficiency:

• More lean muscle and less body fat, especially around the waist
• Better bone density over time
• Improved energy, exercise capacity and quality of life for many
• Better cholesterol levels in some people

Why it only helps growth before growth plates close

Height increase depends on open growth plates. Once these fuse, usually in the late teens, somatropin can no longer increase height. In adults, it is used for its metabolic and body composition effects, not growth.

Why doctors monitor IGF-1

Because most of growth hormone's effects run through IGF-1, doctors use blood IGF-1 levels to judge whether the dose is right. Too low means the dose may need raising; too high raises the risk of side effects and is avoided.

Uses of Somatropin

Approved uses vary by brand and country. The most common are listed below.

Who is it for?

Somatropin is for children and adults with a confirmed diagnosis, usually made by a pediatric or adult endocrinologist. Diagnosis often involves:

• Careful growth measurements over time (in children)
• Blood tests for IGF-1 and other pituitary hormones
• Growth hormone stimulation tests, where medicines are given to see whether the pituitary releases enough GH
• Bone age X-rays and, often, a brain MRI

Who should not use it?

• People with active cancer
• People who are critically ill after open-heart or abdominal surgery, major trauma or acute respiratory failure (higher death rates were seen in studies)
• Children with Prader-Willi syndrome who are severely obese, have severe breathing problems or untreated sleep apnea
• People with active proliferative or severe diabetic retinopathy
• Children whose growth plates have closed, when the aim is to increase height
• People allergic to somatropin or ingredients in the product (some contain preservatives such as metacresol or benzyl alcohol)
• Healthy adults wanting it for anti-aging, weight loss or muscle building

How is Somatropin taken?

Somatropin is given as a small injection under the skin, usually once a day, most often in the evening to match the body's natural night-time GH release. Common sites are the thigh, belly, buttock or back of the upper arm. Most families and adult patients learn to inject at home using a pen device after training from a nurse.

Typical prescribed doses

Doses are based on body weight (children) or adjusted to IGF-1 levels (adults), and differ slightly between brands. The ranges below come from prescribing information and are shown only to explain medical use; your endocrinologist sets your dose.

Women taking oral estrogen often need higher doses, because oral estrogen reduces the liver's response to GH.

Practical tips

• Inject at about the same time each evening.
• Rotate injection sites to avoid lumps or loss of fat under the skin (lipoatrophy).
• Follow the instructions for your specific pen or vial; some must be mixed before use, which should be done gently without shaking.
• Missed dose: skip it and take the next dose at the usual time. Do not double up.
• Storage: most products are kept in the **refrigerator (2–8°C / 36–46°F)** and must not be frozen. Some can be kept at room temperature for a limited time; check your product leaflet.
• Dispose of needles in a proper sharps container.
• Keep a growth chart or diary, and bring it to clinic visits.

Precautions, monitoring and interactions

Tell your doctor about every health condition and medicine before starting somatropin. Key precautions include:

• Cancer history: people who had cancer, especially childhood cancer survivors treated with radiation to the head, need close monitoring for new tumors.
• Raised pressure in the skull (intracranial hypertension): report persistent headaches, vision changes, nausea or vomiting, especially early in treatment.
• Slipped capital femoral epiphysis (SCFE): in growing children, a new limp or hip or knee pain needs prompt assessment.
• Scoliosis: existing curvature of the spine may worsen during rapid growth.
• Blood sugar: GH reduces insulin sensitivity. People with diabetes or at risk need sugar monitoring; medicines may need adjusting.
• Thyroid: somatropin can unmask an underactive thyroid, so thyroid tests are checked.
• Cortisol: in people with pituitary disease, it can unmask low cortisol (adrenal insufficiency), which can be serious.
• Prader-Willi syndrome: sleep studies and weight control are needed before and during treatment because of a risk of breathing problems during sleep.
• Pancreatitis: rare, but report severe belly pain.