Growth Hormone Deficiency: Diagnosis and Treatment

Somatostatin and Growth Hormone Regulation

1 in 3,480 adults affected

Adult growth hormone deficiency is underdiagnosed, affecting body composition, bone density, cardiovascular risk, and quality of life. Diagnosis requires provocative testing because random GH levels are unreliable.

Stochholm et al., European Journal of Endocrinology, 2006

Stochholm et al., European Journal of Endocrinology, 2006

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Growth hormone is a 191-amino acid peptide released in pulses from the anterior pituitary, controlled by two opposing hypothalamic signals: growth hormone-releasing hormone (GHRH) stimulates release, while somatostatin suppresses it. When the system fails, whether from pituitary damage, hypothalamic disease, or idiopathic causes, growth hormone deficiency (GHD) develops. In adults, this is not merely a matter of lost height potential. GHD produces a clinical syndrome of increased visceral adiposity, reduced lean mass, decreased bone density, impaired lipid profiles, cardiovascular dysfunction, and diminished quality of life. The condition affects approximately 1 in 3,480 adults, though many cases go undiagnosed because symptoms overlap with normal aging. For how GH secretion patterns work in health, see why growth hormone is released in pulses.

What causes growth hormone deficiency in adults

Adult GHD divides into two categories. Childhood-onset GHD persists into adulthood in approximately 25% of cases; the remainder resolve, suggesting the developing brain had a different threshold for GH axis maturation. Adult-onset GHD is acquired, most commonly from pituitary adenomas (or their treatment with surgery or radiation), traumatic brain injury, subarachnoid hemorrhage, or infiltrative diseases like sarcoidosis and hemochromatosis.

Idiopathic GHD, where no structural cause is identified, accounts for a smaller proportion of adult cases but is the most diagnostically challenging. Because GH is secreted in pulses and levels are undetectable for most of the day, a single random GH measurement is clinically useless. IGF-1 (insulin-like growth factor-1), which reflects integrated GH activity over time, is more informative but has significant overlap between GHD and normal populations, particularly in the elderly and obese. For how the GH/IGF-1 relationship works mechanically, see the GH/IGF-1 axis explained.

Diagnosis: provocative testing and the macimorelin breakthrough

Because baseline measurements are insufficient, GHD diagnosis requires provocative stimulation tests that challenge the pituitary to produce a maximal GH response.

The insulin tolerance test

The insulin tolerance test (ITT) has been the gold standard since the 1960s. Intravenous insulin is administered to induce symptomatic hypoglycemia (blood glucose below 40 mg/dL), which is a potent stimulus for GH release. A peak GH response below 3-5 mcg/L (depending on the guideline) confirms severe GHD. The ITT simultaneously tests the hypothalamic-pituitary-adrenal axis, making it efficient for patients with suspected panhypopituitarism.

The drawbacks are considerable. The test requires physician supervision throughout, carries risks of seizures and altered consciousness in susceptible patients, and is contraindicated in patients over 65 or those with cardiovascular disease, epilepsy, or adrenal insufficiency. These limitations have driven the search for alternatives.

GHRH-arginine test

The GHRH-arginine test combines intravenous GHRH (1 mcg/kg) with arginine infusion. It was widely used until 2008 when the GHRH preparation was discontinued in the United States. BMI-adjusted cutoffs improved accuracy: peak GH below 11 mcg/L for BMI under 25, below 8 mcg/L for BMI 25-30, and below 4 mcg/L for BMI over 30. This test had 95% sensitivity and 91% specificity for GHD. The unavailability of GHRH created a diagnostic gap that macimorelin ultimately filled.

Macimorelin: the oral peptide diagnostic

Macimorelin (Macrilen) is an oral ghrelin receptor agonist that stimulates GH release by activating growth hormone secretagogue receptors (GHSR-1a) in the pituitary and hypothalamus. Garcia et al. (2013) validated the macimorelin test in a multicenter study, finding 92% concordance with the ITT using a peak GH cutoff of 2.8 mcg/L.^[1] The test is administered as a single oral dose, requires only three blood draws over 90 minutes, and has no contraindications related to cardiovascular disease or seizure history.

Wang et al. (2025) elucidated the molecular mechanism by which macimorelin binds the GHSR receptor, revealing distinct binding modes compared to ghrelin and the related drug anamorelin.^[2] Understanding these structural differences informs the design of next-generation ghrelin mimetics with improved diagnostic or therapeutic profiles.

The FDA approved macimorelin for adult GHD diagnosis in 2017, making it the first oral test for this condition. Current guidelines from the Growth Hormone Research Society (2019) recommend the ITT, macimorelin, and glucagon stimulation test as validated options. The arginine-alone test is no longer recommended due to poor sensitivity.

Symptoms and clinical features

Adult GHD produces a constellation of non-specific symptoms that overlap with depression, hypothyroidism, and normal aging. This overlap explains the high rate of underdiagnosis.

Body composition changes: Increased visceral adiposity with redistribution of fat from peripheral to central depots. Reduced lean body mass with preserved or increased total body weight. The visceral fat and growth hormone connection covers this relationship in detail.

Metabolic effects: Adverse lipid profiles with increased LDL cholesterol and decreased HDL. Increased insulin resistance. Elevated inflammatory markers including C-reactive protein and interleukin-6.

Bone: Decreased bone mineral density, particularly at the lumbar spine and femoral neck. Increased fracture risk that improves with GH replacement over 2-5 years.

Cardiovascular: Reduced cardiac output, increased arterial intima-media thickness, endothelial dysfunction, and a 1.5-2 fold increased cardiovascular mortality risk in untreated GHD.

Quality of life: Fatigue, social isolation, reduced exercise capacity, impaired concentration, and decreased emotional well-being as measured by the QoL-AGHDA (Quality of Life Assessment of GH Deficiency in Adults) questionnaire.

Vergani et al. (2021) investigated the ghrelin-LEAP-2 axis in adult GHD and found that ghrelin levels were reduced in GHD patients compared to controls, while the LEAP-2/ghrelin ratio was elevated.^[3] LEAP-2 (liver-expressed antimicrobial peptide-2) is an endogenous ghrelin antagonist. This shifted ratio may represent a metabolic adaptation to the insulin resistance and increased fat mass characteristic of GHD, suggesting the appetite-GH signaling axis is disrupted at multiple levels in this condition.

Treatment: GH replacement therapy

Recombinant human GH

Daily subcutaneous injections of recombinant human growth hormone (rhGH) have been the standard treatment since the 1990s. Available formulations (somatropin) include Genotropin, Norditropin, Humatrope, Omnitrope, and Saizen. Dosing is individualized, starting at 0.2-0.3 mg/day and titrated based on IGF-1 levels, clinical response, and side effects. The target is an IGF-1 in the upper half of the age-adjusted normal range.

Treatment consistently improves body composition (decreased fat mass, increased lean mass), bone density (after 2+ years), lipid profiles, and quality of life scores. Cardiovascular outcomes data are observational but suggest reduced mortality with treatment. The primary limitations are the daily injection burden and cost (approximately $800-1,500/month without insurance in the United States).

Long-acting formulations

The shift to weekly GH administration represents a major advance in treatment convenience. Somapacitan (Sogroya), approved by the FDA in 2020, uses albumin binding to extend the half-life. Lonapegsomatropin (Skytrofa), initially approved for pediatric GHD, had its indication expanded to adults in 2025.

Liu et al. (2025) tested an Fc-growth hormone fusion protein in rhesus macaques and demonstrated dose-dependent half-life extension: 23.7 hours at the lowest dose, increasing to 76.1 hours at the highest dose.^[4] IGF-1 and IGFBP-3 levels remained elevated for 28-42 days after injection. No adverse effects were observed across single doses up to 62.5 mg/kg and repeated doses over 29 weeks. This Fc-fusion approach joins other long-acting strategies including PEGylation and transcon technology in the pipeline for next-generation GH therapies.

Peptide secretagogues: stimulating endogenous GH

Rather than replacing GH directly, several peptide classes stimulate the body's own GH production. None are FDA-approved for adult GHD, but they represent an active area of research and off-label clinical use.

GHRH analogs (sermorelin, CJC-1295, tesamorelin): These act on pituitary GHRH receptors. Tesamorelin is the only FDA-approved GHRH analog, but specifically for HIV-associated lipodystrophy, not GHD. Sermorelin was previously FDA-approved for pediatric GHD diagnosis but was withdrawn from the market. CJC-1295 and its effects on IGF-1 are documented in research settings. For the upstream hypothalamic signal, see GHRH: the growth hormone releasing signal.

Growth hormone releasing peptides (GHRP-2, GHRP-6, hexarelin): These synthetic peptides activate the ghrelin receptor (GHSR-1a) to stimulate GH release. GHRP-6 also produces pronounced hunger through the same receptor system. GHRP-2 is used diagnostically in some countries for GHD testing.

Oral ghrelin mimetics (MK-677/ibutamoren): MK-677 increases GH and IGF-1 levels through oral dosing, but has not completed regulatory approval for any indication. It raises fasting glucose and appetite as expected from ghrelin receptor activation.

Leone et al. (2020) demonstrated that GHRH deficiency in mice promotes inflammation-associated carcinogenesis through mechanisms independent of GH/IGF-1 levels.^[5] GHRH-deficient mice showed increased pro-inflammatory cytokines (TNF-alpha, IL-6) and accelerated colon carcinogenesis, suggesting GHRH has direct anti-inflammatory roles in peripheral tissues beyond its GH-releasing function. This finding raises the question of whether GHRH analog therapy might provide benefits that GH replacement alone does not.

The question of whether growth hormone stimulation (via peptides) is superior to growth hormone replacement (via rhGH) for adult GHD lacks a definitive answer. Secretagogues preserve pulsatile GH patterns and feedback regulation, which direct GH replacement bypasses. But pulsatile delivery also means lower and less predictable peak GH levels. For the related debate about whether growth hormone peptides can build muscle and the relationship between GH pulses and sleep quality, the evidence remains mixed.

Monitoring and long-term considerations

GH replacement dosing is guided by serum IGF-1, maintained in the upper half of the age-appropriate normal range. Over-replacement risks fluid retention, carpal tunnel syndrome, joint pain, and theoretical concerns about cancer promotion, addressed in the growth hormone cancer debate. Under-replacement leaves patients symptomatic with persistent body composition abnormalities.

Monitoring every 6-12 months includes IGF-1, fasting glucose, lipid panel, and body composition assessment. Bone densitometry should be performed at baseline and every 2 years. MRI surveillance is needed for patients with known pituitary pathology.

For pediatric GHD, the treatment landscape and diagnostic approach differ; see growth hormone deficiency in children for that evidence base.

What remains uncertain

The optimal duration of GH replacement in adults is undefined. Most guidelines recommend indefinite treatment if benefit is demonstrated, but long-term data beyond 10-15 years is limited. Whether treatment should be adjusted in elderly patients (over 70) who have physiological GH decline is debated.

The role of combination secretagogue therapy (GHRH analog + GHRP) versus monotherapy GH replacement has not been tested in a randomized trial for adult GHD. Small studies suggest combination secretagogues produce GH pulses that more closely mimic physiology, but clinical superiority has not been established.

Whether GH replacement modifies cardiovascular mortality in GHD, versus merely improving surrogate markers, remains an open question. Observational data is consistent with benefit, but no randomized mortality trial has been conducted or is likely to be.

The Bottom Line

Adult growth hormone deficiency is a clinical syndrome characterized by adverse body composition, metabolic, cardiovascular, and quality of life changes. Diagnosis requires provocative testing; macimorelin, an oral ghrelin receptor agonist, has joined the ITT as an FDA-approved diagnostic option. Treatment with daily recombinant GH is effective, and weekly long-acting formulations are transforming the convenience equation. Peptide-based secretagogues that stimulate endogenous GH release represent an alternative approach under investigation, though none are approved for GHD treatment.

Frequently Asked Questions

How is growth hormone deficiency diagnosed in adults?

Adult GHD requires provocative stimulation testing because random GH levels are undetectable for most of the day. The insulin tolerance test (ITT) is the gold standard, with GHD confirmed at peak GH below 3-5 mcg/L. Macimorelin, an oral ghrelin agonist, was FDA-approved in 2017 as an alternative with 92% concordance versus ITT (Garcia et al., 2013). The glucagon stimulation test is also validated.

What are the symptoms of growth hormone deficiency in adults?

Adult GHD causes increased belly fat, reduced muscle mass, decreased bone density, adverse cholesterol profiles, fatigue, reduced exercise capacity, and impaired quality of life. These symptoms overlap with normal aging, which is why the condition is underdiagnosed. Cardiovascular mortality risk is 1.5-2 times higher in untreated GHD patients.

What is macimorelin and how does it test for GH deficiency?

Macimorelin (Macrilen) is an oral ghrelin receptor agonist that stimulates GH release. A single oral dose is given, and blood is drawn at 30, 45, and 60 minutes. A peak GH below 2.8 mcg/L confirms GHD. The test requires no IV access, has no cardiovascular contraindications, and takes about 90 minutes to complete (Garcia et al., 2013).

How is adult growth hormone deficiency treated?

Standard treatment is daily subcutaneous injections of recombinant human growth hormone (somatropin), dosed at 0.2-0.3 mg/day and adjusted based on IGF-1 levels. Weekly long-acting formulations (somapacitan, lonapegsomatropin) are now available and approved. Treatment improves body composition, bone density, lipid profiles, and quality of life. Peptide secretagogues that stimulate endogenous GH production are used off-label but are not FDA-approved for GHD.

Can peptides like GHRP-6 or MK-677 treat growth hormone deficiency?

Growth hormone releasing peptides (GHRP-2, GHRP-6, hexarelin) and oral ghrelin mimetics (MK-677/ibutamoren) stimulate endogenous GH release and can elevate IGF-1 levels. However, none are FDA-approved for treating GHD. They preserve pulsatile GH patterns, but produce less predictable GH levels than direct GH replacement. Clinical trials comparing secretagogues to rhGH for GHD outcomes have not been conducted.

Do you need growth hormone injections every day?

Daily injections were the only option until recently. Somapacitan (Sogroya), approved in 2020, allows weekly injections for adult GHD. Lonapegsomatropin was expanded to adult use in 2025. Fc-GH fusion proteins under development show half-lives exceeding 60 hours in primate models (Liu et al., 2025), suggesting even less frequent dosing may become possible.