Growth Hormone (GH) & IGF-1

Growth hormone drives growth in childhood and supports tissue repair and metabolism throughout life. It works largely through a second hormone, IGF-1, which carries out many of its effects on the body.

What growth hormone and IGF-1 are

Growth hormone (GH, also called somatotropin) is a protein (peptide) hormone, not a steroid, so it acts on receptors at the cell surface rather than entering cells the way steroid hormones do. Once released, it travels to the liver and other tissues, prompting them to make insulin-like growth factor 1 (IGF-1). IGF-1 mediates many of GH's growth-promoting actions and circulates at steadier levels than GH itself, which is released in short bursts. In effect, GH is the fast, pulsing signal and IGF-1 is the slower, more constant messenger that carries much of the work forward.

GH also has some direct effects of its own, particularly on metabolism, that are separate from IGF-1. This is why the system is best understood as a partnership: GH and IGF-1 share growth-promoting duties, but they do not do exactly the same things.

Where they are produced

Growth hormone is produced by specialized cells (somatotrophs) in the anterior pituitary gland at the base of the brain. IGF-1 is produced mainly by the liver in response to GH, with smaller amounts made locally in other tissues such as bone and muscle, where it can act right where it is made. This two-step arrangement — GH from the pituitary, IGF-1 largely from the liver — is central to how the system works and to how it is tested.

What they do across body systems

• Growth in childhood: In children and adolescents, GH and IGF-1 drive the lengthening of bones at the growth plates and the growth of soft tissues, contributing to height until the growth plates close.
• Bone and muscle: They support the maintenance of bone density and muscle mass into adulthood.
• Tissue maintenance and repair: In adults, the system supports ongoing repair and turnover of several tissues.
• Metabolism: GH influences how the body uses fats and carbohydrates; it tends to promote the breakdown of fat for energy and can oppose some of insulin's actions, which is part of how it helps regulate body composition.
• Fluid and minerals: The system has modest effects on fluid balance and mineral handling.
• Other influences: Sleep, exercise, nutrition, and stress all affect GH release, linking the hormone to daily physiology.

Regulation and the feedback loop

GH release is controlled by the hypothalamus through two opposing signals: growth hormone–releasing hormone (GHRH), which stimulates release, and somatostatin, which suppresses it. A stomach-derived hormone, ghrelin, also stimulates GH release, which helps tie the system to feeding and fasting. The pituitary releases GH in pulses, often largest during deep sleep. As GH rises and IGF-1 increases, IGF-1 feeds back to the hypothalamus and pituitary to slow further GH release — a negative feedback loop that keeps the system in check. Because GH is released in bursts and changes quickly, a single random GH measurement can be hard to interpret, which is one reason IGF-1, with its steadier levels, is often measured instead.

Why GH is one of the hardest hormones to measure

Many hormones can be read reasonably well from a single blood draw, but GH is a notable exception, and understanding why explains how the system is tested. GH is released in brief pulses rather than at a steady rate, so two samples taken hours apart from the same healthy person can look very different — one might catch a peak and another a trough. On top of that, GH rises with deep sleep, exercise, fasting, and stress, and falls after eating, so the value depends heavily on what the person was doing beforehand. A single random number therefore carries little meaning on its own. The body's design partly solves this for clinicians: because GH drives the liver to make IGF-1, and IGF-1 changes slowly and stays relatively constant through the day, IGF-1 acts as a smoothed-out average of recent GH activity. When the question is about deficiency or excess rather than a quick snapshot, clinicians turn to dynamic tests that deliberately stimulate or suppress GH under controlled conditions, which give a far more reliable answer than chance timing of a single draw.

What high or low levels can be associated with

In childhood, lower GH activity can be associated with slower growth and short stature, while higher activity can be associated with excessive growth. In adults, a sustained excess (often from a pituitary tumor) can be associated with the gradual enlargement of hands, feet, and facial features, while a deficiency can be associated with changes in body composition, bone density, and energy. Certain pituitary conditions can raise or lower GH and IGF-1. These associations are qualitative and require careful clinical evaluation; see the conditions index for related topics.

Where the evidence is limited

Growth hormone is sometimes promoted as an "anti-aging," fitness, or rejuvenation product, because GH and IGF-1 decline gradually with age. It is important to be clear that these claims are not well supported. A natural decline with age does not establish that adding GH reverses aging or safely improves health, fitness, or appearance in people who are not deficient. Outside of a diagnosed deficiency managed by a specialist, evidence for benefit is limited, and GH can carry meaningful effects on blood sugar, fluid balance, and joints. Products sold as GH "boosters," "releasers," or "secretagogues" are likewise not established to provide the benefits often claimed. This page does not endorse such use; decisions about GH belong with a clinician. See the treatments index for how the site frames therapies generally.

How they relate to other hormones

The GH–IGF-1 system interacts with several other hormones. Thyroid hormone and adequate sex hormones are needed for normal growth, so deficiencies elsewhere can blunt growth even when GH is present. GH partly opposes insulin's action on blood sugar, linking it to glucose metabolism. And because pituitary tumors or damage can affect several hormones at once, GH problems are sometimes found alongside changes in other pituitary outputs. For a broader map, see the hormones index and the glossary.

How they are measured in blood

Because GH is released in pulses, clinicians often measure IGF-1, which reflects average GH activity more stably and is interpreted against age- and sex-specific reference intervals. When GH itself is assessed, it is usually through stimulation tests (to look for too little) or suppression tests (to look for too much) done under controlled conditions, rather than a single random draw. These dynamic tests are arranged and interpreted by a clinician. See the blood tests overview for context, and the glossary for terms.

The entries above are illustrative only and not diagnostic thresholds; values depend on the laboratory, the assay, the testing protocol, age, and sex.