Human growth hormone, commonly called HGH or simply growth hormone, is one of the body’s major metabolic hormones. Although it is best known for helping children grow, growth hormone remains active throughout adulthood and continues to influence body composition, bone health, metabolism and tissue maintenance.
Growth hormone is produced naturally by the pituitary gland and released into the bloodstream in pulses rather than at a constant rate. Many of its effects also involve another hormone called insulin-like growth factor 1, or IGF-1. Understanding this relationship helps explain why HGH continues to matter long after a person has stopped growing taller.
What Is Human Growth Hormone?
Human growth hormone is a peptide hormone produced by the anterior portion of the pituitary gland, a small endocrine gland located at the base of the brain. The medical abbreviation is GH, although HGH is commonly used when referring specifically to human growth hormone.
In children and adolescents, one of growth hormone’s most obvious roles is promoting normal physical growth. It contributes to the growth of bones and other tissues while the growth plates remain open. Once those growth plates have fused, additional growth hormone cannot make an adult taller.
That does not mean growth hormone becomes unnecessary after puberty. Adults continue producing GH throughout life because it has important roles in metabolism, bone and tissue maintenance, body composition and the regulation of several other biological processes.
Where Does HGH Come From?
Growth hormone production is controlled through communication between the hypothalamus and pituitary gland. The hypothalamus is an area of the brain involved in regulating many automatic and hormonal functions, while the pituitary releases hormones that communicate with tissues throughout the body.
Two important signals help control growth hormone secretion. Growth hormone-releasing hormone, or GHRH, stimulates the pituitary to release GH, while somatostatin inhibits its release. The balance between these and other signals allows GH levels to rise and fall throughout the day.
Growth hormone is therefore not normally released at one steady level. Instead, the pituitary produces short bursts known as pulses, with periods of relatively low circulating GH between them. This pulsatile pattern is an important part of how the natural growth hormone system functions.
How Does HGH Work?
Growth hormone can act directly on tissues, but many of its effects are also mediated through insulin-like growth factor 1. When GH reaches the liver and other tissues, it stimulates the production of IGF-1, which then carries out many of the growth and tissue-related effects associated with the growth hormone system.
This relationship is commonly referred to as the GH/IGF-1 axis. Growth hormone stimulates IGF-1 production, while rising IGF-1 levels also help signal the brain and pituitary to reduce additional GH secretion. This feedback system prevents normal hormone production from simply continuing unchecked.
GH and IGF-1 are closely connected, but they are not interchangeable hormones. Growth hormone has direct metabolic effects of its own, while IGF-1 performs many of the growth-promoting and tissue-supporting functions stimulated by GH.
What Does HGH Do in Adults?
The word “growth” can make HGH sound primarily like a childhood hormone, but its role in adults is much broader. Normal growth hormone activity helps maintain healthy body structure and participates in the regulation of muscle tissue, body fat, bone and metabolism.
One important area is body composition. Growth hormone influences the way the body stores and uses fat and is involved in maintaining lean tissue. Adults with clinically significant growth hormone deficiency can experience changes in fat distribution and lean mass, demonstrating that GH continues to have metabolic importance after physical growth has finished.
Growth hormone also contributes to normal bone metabolism and skeletal integrity. Bone is constantly being broken down and rebuilt throughout adulthood, and the GH/IGF-1 system is one of several hormonal systems involved in maintaining this process.
GH also interacts with carbohydrate and lipid metabolism. These effects are complex because growth hormone, IGF-1 and insulin all influence nutrient metabolism in different ways. Both too little and too much growth hormone can disrupt normal physiology, which is why medically prescribed growth hormone therapy is monitored rather than simply adjusted according to how someone feels.
The effects of HGH on muscle, fat loss and physical recovery deserve more detail than can reasonably fit into a general introduction. These areas are covered separately in our guide to HGH and body composition, muscle growth, fat loss and recovery.
When Does the Body Release Growth Hormone?
Growth hormone secretion changes considerably throughout a 24-hour period. Rather than maintaining a predictable concentration in the bloodstream, GH rises sharply during individual pulses and can then fall to very low levels between those pulses.
Some of the largest natural GH pulses are associated with sleep, particularly during the early portion of the night. Exercise, nutritional status, blood glucose, amino acids and other hormonal signals can also influence growth hormone secretion.
Age also affects this pattern. Natural growth hormone secretion is generally higher during childhood and adolescence and gradually declines during adulthood. However, a normal age-related reduction in GH is not the same thing as having a diagnosed growth hormone deficiency.
This distinction is important because lower GH or IGF-1 levels in an older adult do not automatically mean that growth hormone treatment is necessary. Clinical growth hormone deficiency is a specific endocrine disorder that requires appropriate medical evaluation.
HGH and IGF-1: What Is the Difference?
HGH and IGF-1 are often discussed together because they form part of the same hormonal system, but they perform different functions. HGH is released primarily by the pituitary gland and acts as one of the signals that stimulates IGF-1 production.
Much of circulating IGF-1 is produced by the liver in response to growth hormone, although other tissues can produce IGF-1 locally as well. IGF-1 then interacts with receptors throughout the body and contributes to effects involving bone, cartilage and other tissues.
There is another practical difference between the two hormones: their blood levels behave differently. Growth hormone can rise and fall dramatically over relatively short periods, while IGF-1 tends to remain considerably more stable. This is one reason IGF-1 measurements can provide useful information when doctors are evaluating the growth hormone system.
We will cover this relationship in considerably more detail in a dedicated guide to the HGH and IGF-1 axis.
Why a Single HGH Blood Test Can Be Misleading
Because HGH is released in pulses, a random blood test can capture either a temporary peak or one of the periods when very little growth hormone is circulating. A low GH reading at one moment therefore does not necessarily mean that someone has a growth hormone deficiency.
Doctors evaluating suspected GH disorders may measure IGF-1 and, when appropriate, use specialized growth hormone stimulation or suppression testing. These tests evaluate how the growth hormone system responds under controlled conditions rather than relying entirely on a single random GH measurement.
Testing is an important topic on its own, particularly because GH and IGF-1 results are frequently misunderstood. A separate guide will look more closely at HGH blood tests, IGF-1 levels and how growth hormone deficiency is evaluated.
What Is Synthetic HGH?
The growth hormone used as medication is manufactured using recombinant DNA technology and is generally referred to as recombinant human growth hormone. The pharmaceutical name somatropin is commonly used for recombinant GH products.
Somatropin is designed to reproduce the biological activity of naturally occurring human growth hormone. Prescription growth hormone is used medically for specific conditions, including confirmed growth hormone deficiency and certain other approved indications depending on the patient and jurisdiction.
Synthetic HGH should not be confused with supplements marketed as “HGH boosters,” “HGH releasers” or similar products. Growth hormone itself is a peptide hormone, and genuine pharmaceutical growth hormone is not simply an over-the-counter nutritional supplement.
For Canadians, the rules surrounding prescription HGH, approved somatropin products and the legal status of obtaining growth hormone are covered separately in our guide to HGH laws and prescriptions in Canada.
Is HGH the Same as Somatropin?
In everyday discussion, HGH and somatropin are often used almost interchangeably, but there is a small distinction. HGH can refer broadly to human growth hormone, including the hormone naturally produced by the body, while somatropin refers to manufactured recombinant human growth hormone used as a medication.
Modern recombinant somatropin has the same 191-amino-acid sequence as the main form of human growth hormone naturally produced by the pituitary. Different pharmaceutical HGH products can still differ in their formulation, delivery device, concentration, approved indications and storage requirements.
Those differences matter when handling prescription HGH. Storage and reconstitution instructions should always be based on the specific product being used rather than assuming that every HGH product has identical requirements. Our HGH reconstitution and storage guide covers that subject separately and works alongside the HGH reconstitution calculator.
Can HGH Make an Adult Taller?
No. Once the growth plates at the ends of the long bones have fused, growth hormone cannot restart normal height growth. Growth plates typically close following puberty, which is why HGH has very different effects in adults than it does in growing children.
Extremely high growth hormone levels in adults can still cause abnormal tissue and bone changes, but this is not the same as becoming taller. Chronic excessive GH production in adulthood is associated with a medical condition called acromegaly and requires medical evaluation and treatment.
Is Growth Hormone Still Important After 40?
Growth hormone production generally declines with age, but adults continue producing it throughout life. The GH/IGF-1 system remains involved in normal metabolism, body composition, bone maintenance and other physiological processes well beyond early adulthood.
It is important, however, to separate normal age-related hormonal changes from true growth hormone deficiency. Lower GH secretion with advancing age does not by itself establish a medical reason to use prescription growth hormone.
The relationship between HGH, aging and claims surrounding “anti-aging” treatment is substantial enough that we will examine it separately rather than trying to answer it in a few paragraphs here.
The Bottom Line
Human growth hormone is much more than a hormone that makes children grow. Produced by the pituitary gland and closely connected with IGF-1, GH remains part of the body’s metabolic and tissue-regulation systems throughout adulthood.
Its effects involve body composition, bone metabolism, nutrient metabolism and the maintenance of normal tissues, while its natural secretion follows a highly variable pulsatile pattern. This also explains why understanding HGH requires looking at the entire GH/IGF-1 system rather than focusing on a single growth hormone blood level.
For anyone concerned about abnormal growth hormone levels or possible growth hormone deficiency, proper medical testing is more useful than trying to interpret symptoms or a single laboratory value in isolation. From here, the individual subjects of HGH body composition, side effects, Canadian prescription rules, testing, anti-aging research and HGH reconstitution can each be explored in greater detail without trying to force every aspect of growth hormone into one guide.
Medical Disclaimer: This guide is for educational purposes only and is not a substitute for medical advice or the instructions provided with a prescribed HGH product. Human growth hormone (HGH) is a prescription medication in Canada. Reconstitution, storage and handling requirements can vary by product, so always follow the manufacturer’s instructions and guidance from your pharmacist or healthcare provider.