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IGF-1 and human growth hormone (GH or HGH) are closely related but they are not the same hormone. Growth hormone is produced by the pituitary gland and stimulates the liver and other tissues to produce IGF-1. IGF-1 then mediates many of growth hormone’s effects on growth and tissue metabolism.
Written and medically reviewed by David Nazarian, MD — Board Certified in Internal Medicine.
What Is Growth Hormone?
Growth hormone is secreted in pulses, especially during sleep. Because levels rise and fall throughout the day, a random growth-hormone level is usually not useful for diagnosing a growth-hormone disorder.
What Is IGF-1?
IGF-1 is produced primarily by the liver in response to growth hormone and remains more stable in the bloodstream. For that reason, IGF-1 is often used as an initial laboratory marker when clinicians evaluate suspected growth-hormone excess or deficiency.
Is IGF-1 the Same as HGH?
No. HGH (growth hormone) is produced by the pituitary gland and signals tissues—including the liver—to produce IGF-1. IGF-1 is one of the major downstream mediators of growth-hormone action. They are part of the same physiologic pathway, but they are different hormones and are tested and treated differently.
What About IGF-1 LR3 vs HGH?
IGF-1 LR3 is a modified research form of IGF-1 and should not be confused with prescription recombinant human IGF-1 used for specific medical indications. An FDA substance identifier does not mean a product is FDA-approved. Patients should not treat IGF-1 LR3 as interchangeable with prescription growth hormone or approved IGF-1 therapy.
Are HGH and IGF-1 Used for Anti-Aging or Fat Loss?
Neither should be used simply to pursue anti-aging, muscle gain or routine weight loss in otherwise healthy adults. Prescription growth hormone and recombinant IGF-1 have specific medical indications and can cause clinically important adverse effects.
How Growth Hormone Disorders Are Diagnosed
Diagnosis requires clinical context and specialized testing. Suspected deficiency may require stimulation testing, while suspected growth-hormone excess may require IGF-1 testing and suppression testing. A single hormone level should not be interpreted in isolation.
What Are the Risks?
Growth-hormone and IGF-1 therapies can affect glucose metabolism, fluid balance, soft tissues and other organ systems. Treatment should therefore be limited to appropriate indications and monitored by a clinician familiar with endocrine disease.
Which Test Is More Useful?
IGF-1 is generally more useful than a random growth-hormone level because IGF-1 is more stable. The correct test depends on the suspected disorder and the patient’s age, symptoms and medical history.
For more information, see our IGF-1 testing and therapy, hormone testing, and growth hormone deficiency treatment pages. If your concern is based on symptoms or abnormal laboratory results, schedule a physician-led evaluation.
