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Sermorelin · Mechanism

What is growth hormone-releasing hormone (GHRH)?

The upstream signal, not the hormone. Where GHRH is made, how it reaches the pituitary, why growth hormone comes out in pulses, and what the measured age-related decline actually is.

Medically reviewed by the Kesbury Health Clinical Team · Last updated 2026-09-02

Quick answer

Growth hormone-releasing hormone (GHRH) is a hormone made in the hypothalamus whose job is to signal the anterior pituitary gland to produce and release growth hormone. It is not growth hormone itself. It is the upstream instruction. GHRH is a peptide, a short chain of amino acids; the full human form is 44 amino acids long and the first 29 carry the biological activity, which is why the pharmaceutical analog of that fragment appears in the research literature as GHRH(1-29) and in the clinic as sermorelin. The GHRH signal travels a short private blood supply from the hypothalamus to the pituitary, binds a receptor on somatotroph cells, and triggers a pulse of growth hormone. The size and frequency of those pulses fall with age, which has been measured directly in healthy adults [4].

Where GHRH is made and where it goes

GHRH is produced by neurons in the arcuate nucleus of the hypothalamus. Rather than entering the general circulation, it is released into the hypophyseal portal system, a short dedicated vascular link between the hypothalamus and the anterior pituitary. That anatomy matters: it means a small quantity of hormone reaches its target at high concentration without being diluted across the whole body.

At the pituitary, GHRH binds the GHRH receptor on somatotroph cells. Those cells respond by synthesising and releasing growth hormone into the bloodstream, where it acts on tissues directly and also drives the liver to produce insulin-like growth factor 1 (IGF-1).

Why the output comes in pulses

The growth hormone axis has an accelerator and a brake. GHRH stimulates release; somatostatin, also hypothalamic, inhibits it. The interplay produces bursts rather than a steady level, and the largest bursts are tied to slow-wave sleep. Van Cauter and colleagues reported in 1998 that approximately 70% of daily growth hormone output in men occurs during early sleep throughout adulthood [3], and Obal and Krueger reviewed GHRH's own role as a sleep-promoting substance in 2004 [2].

This is the practical reason IGF-1, not growth hormone, is the marker used to assess the axis. Growth hormone measured at a random moment may be near zero in a completely healthy person simply because no pulse is happening. IGF-1 integrates the signal over a longer window, which is why standardising its assay has been the subject of a formal consensus statement [5].

The GHRH to growth hormone to IGF-1 chain

  1. Hypothalamus releases GHRH into the portal circulation.
  2. Anterior pituitary somatotrophs respond with a pulse of growth hormone.
  3. Liver and peripheral tissues respond to growth hormone; the liver produces IGF-1.
  4. IGF-1 feeds back on the hypothalamus and pituitary, damping further release.

That final feedback step is the reason a GHRH analog behaves differently from injected growth hormone. Supplying growth hormone directly bypasses steps 1 and 2 and the loop that regulates them. Supplying the GHRH signal leaves the pituitary and the feedback in the circuit.

What changes with age

The decline is real and it has been quantified rather than asserted. In a 1991 study of healthy men, each decade of increasing age attenuated the growth hormone production rate by 14% and the half-life of circulating growth hormone by 6%, and relative adiposity independently reduced both the frequency and the amplitude of secretory bursts [4]. A 1992 controlled study found that older men had lower growth hormone and IGF-1 than young men and that twice-daily GHRH(1-29) injections over 14 days reversed that difference [1].

What has not been established is that reversing a laboratory difference reverses anything a person experiences. That gap between a marker and an outcome is the honest boundary of this topic.

GHRH in medicine

The GHRH analog sermorelin has been used diagnostically and therapeutically. A 1999 review covered its use in the diagnosis and treatment of children with idiopathic growth hormone deficiency, where increases in height velocity were sustained through 12 months of treatment [6]. In adults, Endocrine Society guidance for growth hormone deficiency sets out how the axis is evaluated and how therapy is titrated against clinical response and IGF-1 rather than fixed to a chart [7].

Kesbury Health does not prescribe growth hormone. Sermorelin is a different medication, compounded rather than FDA-approved as a finished product, and prescribed after an individual evaluation.

How physician-directed sermorelin works at Kesbury Health

  1. Complete a short online assessment about your goals, symptoms and health history. It takes about 60 seconds to begin.
  2. A licensed Kesbury Health physician reviews what you submitted and decides whether therapy is a reasonable fit for you, or whether something else should be looked at first.
  3. Baseline labs where they apply. The $179 Sermorelin Baseline Panel is a prerequisite for sermorelin therapy, and the results can end the conversation rather than continue it.
  4. If therapy is appropriate, the medication is compounded by a licensed U.S. pharmacy and shipped to your door, with dosing set to you rather than to a chart.
  5. Ongoing physician oversight adjusts the protocol over time, with a 90-day re-evaluation built into the sermorelin program.

Care is delivered by telehealth to residents of the ten states where your Kesbury Health physician is licensed: Alabama, District of Columbia, Delaware, Florida, Maryland, Michigan, New Jersey, Ohio, Pennsylvania and Texas. Eligibility is confirmed during the assessment.

Frequently asked questions

What is GHRH?

Growth hormone-releasing hormone is a hormone made in the hypothalamus that signals the anterior pituitary gland to produce and release growth hormone. It is a peptide of 44 amino acids in its full human form, and the first 29 carry the biological activity. GHRH is not growth hormone; it is the upstream signal that tells the body to make its own.

Where is GHRH made and what does it act on?

It is produced by neurons in the arcuate nucleus of the hypothalamus and released into the hypophyseal portal circulation, a short private blood supply that carries it directly to the anterior pituitary. There it binds the GHRH receptor on somatotroph cells, which respond by releasing growth hormone in a pulse.

What is the difference between GHRH and sermorelin?

Sermorelin is a synthetic version of the biologically active fragment of GHRH, the first 29 amino acids, which is why it appears in the literature as GHRH(1-29). GHRH is the natural hormone; sermorelin is the pharmaceutical analog of its active part.

Why does growth hormone come out in pulses?

Because the axis is regulated by two opposing hypothalamic signals: GHRH, which stimulates release, and somatostatin, which inhibits it. The interaction between them produces bursts rather than a steady level, with the largest bursts tied to slow-wave sleep [3]. This is also why a single random growth hormone measurement tells you very little.

Does GHRH activity change with age?

Yes, and the change has been quantified. A 1991 study of healthy men reported that each decade of increasing age reduced the growth hormone production rate by 14% and the half-life of circulating growth hormone by 6%, with relative adiposity acting as an independent negative factor [4]. A 1992 controlled study found that older men had lower growth hormone and IGF-1 than young men and that twice-daily GHRH(1-29) reversed that difference over 14 days [1].

See what your own axis looks like

Take the free 60-second Kesbury Health assessment. Where sermorelin is under consideration, the baseline panel measures IGF-1 first, and the result is allowed to change the answer.

Start your free 60-second assessment →

Kesbury Health is a LegitScript-certified (#51875982) telehealth longevity practice licensed in ten states. Sermorelin and NAD+ are compounded medications prescribed by a licensed physician after review. Compounded medications are not FDA-approved. This page is educational and is not individualized medical advice. Statements on this page have not been evaluated by the FDA. Individual results vary.

References (primary sources)

Every reference below was checked against its PubMed record on 2026-09-02. Links open the abstract.

  1. Corpas E, Harman SM, Pineyro MA, Roberson R, Blackman MR. Growth hormone (GH)-releasing hormone-(1-29) twice daily reverses the decreased GH and insulin-like growth factor-I levels in old men. Journal of Clinical Endocrinology and Metabolism. 1992;75(2):530-535. doi:10.1210/jcem.75.2.1379256. PMID 1379256.
  2. Obal F Jr, Krueger JM. GHRH and sleep. Sleep Medicine Reviews. 2004;8(5):367-377. doi:10.1016/j.smrv.2004.03.005. PMID 15336237.
  3. Van Cauter E, Plat L, Copinschi G. Interrelations between sleep and the somatotropic axis. Sleep. 1998;21(6):553-566. PMID 9779515.
  4. Iranmanesh A, Lizarralde G, Veldhuis JD. Age and relative adiposity are specific negative determinants of the frequency and amplitude of growth hormone (GH) secretory bursts and the half-life of endogenous GH in healthy men. Journal of Clinical Endocrinology and Metabolism. 1991;73(5):1081-1088. doi:10.1210/jcem-73-5-1081. PMID 1939523.
  5. Clemmons DR. Consensus statement on the standardization and evaluation of growth hormone and insulin-like growth factor assays. Clinical Chemistry. 2011;57(4):555-559. doi:10.1373/clinchem.2010.150631. PMID 21285256.
  6. Prakash A, Goa KL. Sermorelin: a review of its use in the diagnosis and treatment of children with idiopathic growth hormone deficiency. BioDrugs. 1999;12(2):139-157. doi:10.2165/00063030-199912020-00007. PMID 18031173.
  7. Molitch ME, Clemmons DR, Malozowski S, Merriam GR, Vance ML. Evaluation and treatment of adult growth hormone deficiency: an Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology and Metabolism. 2011;96(6):1587-1609. doi:10.1210/jc.2011-0179. PMID 21602453.

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