Adult growth hormone deficiency (AGHD) is a recognized clinical condition with defined diagnostic criteria, FDA-approved treatment, and documented symptoms. It is distinct from the normal age-related decline in growth hormone (GH) secretion that occurs in healthy adults, often called somatopause, and from the supraphysiologic growth hormone use that occurs in athletic doping.

Growth hormone secretion peaks in adolescence and declines by approximately 14% per decade throughout adulthood. By age 60, GH secretion is typically 25-50% of young adult levels. This normal decline is not AGHD; it does not produce the biochemical or clinical profile that meets the criteria for the condition, and treating it with growth hormone replacement is not approved or supported by evidence.

Causes of Genuine Adult GHD

Adult GHD almost always results from damage to the hypothalamus or pituitary, the structures that produce the growth hormone-releasing hormone (GHRH) and growth hormone that drive the system.

Common causes:

  • Pituitary adenoma (benign tumor) treated with surgery or radiation, pituitary function damage is a common consequence of treatment
  • Craniopharyngioma, a tumor near the pituitary that frequently causes hypopituitarism
  • Traumatic brain injury, the pituitary sits in a bony socket (sella turcica) that can be damaged in head trauma
  • Radiation therapy to the brain or head-neck region
  • Hypophysitis (autoimmune pituitary inflammation)

Idiopathic AGHD, occurring without an identifiable cause, is rare in adults and should prompt thorough evaluation before accepting the diagnosis.

How AGHD Presents

Adult GHD produces a recognizable but nonspecific symptom cluster:

  • Reduced lean muscle mass despite regular exercise
  • Increased visceral fat, particularly abdominal
  • Reduced exercise capacity and energy
  • Impaired quality of life, assessed by the Quality of Life Assessment of GHD in Adults (QoL-AGHDA)
  • Reduced bone mineral density over time
  • Adverse lipid profile (lower HDL, higher LDL and triglycerides)

These symptoms overlap with hypothyroidism, low testosterone, depression, and other conditions that need to be excluded before attributing symptoms to GHD.

Diagnosis: Why Random GH Testing Does Not Work

Growth hormone is secreted in pulses, primarily during deep sleep, with very low or undetectable levels between pulses. A random blood GH measurement is virtually meaningless, a normal person can have an undetectable GH at 2 pm because the secretory pulse occurred at 4 am.

Diagnosis requires a dynamic stimulation test:

Insulin tolerance test (ITT): The reference standard. Insulin is injected to induce hypoglycemia, which is a potent stimulus for GH secretion. In normal individuals, GH rises above 5.1 ng/mL (some guidelines use 3 ng/mL as the threshold). A blunted response indicates GHD. The ITT requires close clinical supervision because of hypoglycemia risk.

Glucagon stimulation test: An alternative used when the ITT is contraindicated (history of seizures or cardiovascular disease). Less sensitive than the ITT but safer.

Macimorelin stimulation test: An oral GHRH secretagogue approved specifically for GHD testing in 2017. Growing evidence supports it as an alternative to the ITT with less patient burden.

IGF-1 (insulin-like growth factor-1): A liver-produced hormone whose levels reflect average GH secretion over days. Low IGF-1 in the context of a pituitary lesion and consistent symptoms supports GHD but is not sufficient alone for diagnosis. IGF-1 declines with age, obesity, and malnutrition, reducing its specificity.

Treatment: Recombinant Human Growth Hormone

FDA-approved recombinant human growth hormone (rhGH) is available under multiple brand names (Norditropin, Genotropin, Humatrope, Saizen) and administered by daily subcutaneous injection. Treatment is approved for AGHD in adults with biochemical confirmation.

Documented benefits of rhGH in confirmed AGHD:

  • Improved body composition (reduced fat mass, increased lean mass)
  • Improved exercise capacity
  • Improved bone mineral density over 12-24 months
  • Improved lipid profiles
  • Improved quality of life scores

Starting doses are low (0.1-0.2 mg/day) and titrated upward based on IGF-1 response to avoid side effects: fluid retention, carpal tunnel syndrome, joint pain, and glucose intolerance. Women require higher doses than men because estrogen reduces GH sensitivity.

What AGHD Treatment Is Not

Human growth hormone is heavily promoted in anti-aging contexts and by direct-to-consumer wellness clinics. The FDA has specifically stated that growth hormone is not approved for anti-aging, bodybuilding, or general wellness. The normal age-related GH decline does not constitute GHD.

Prescribing and using rhGH outside of medical necessity is associated with significant costs, risks (glucose intolerance, potential cancer concerns), and legal issues. HGH is a Schedule II controlled substance.

For how growth hormone interacts with testosterone in men’s hormone panels, see How to Read a Hormone Blood Panel: Key Values Explained.