Growth hormone-releasing hormone (GHRH) is the hypothalamic peptide that tells the pituitary to release growth hormone (GH). Native GHRH is rapidly degraded in blood, so research and drug development have produced a family of modified analogs designed to last longer or resist enzymatic breakdown. Three come up repeatedly in the literature: tesamorelin, sermorelin and CJC-1295. They are often discussed as if they were interchangeable, but they differ in structure, duration of action, and the quality of the evidence behind them. This article compares them. For the clinical trial history of tesamorelin specifically, see our in-depth tesamorelin overview.
The Axis They Act On
GH secretion is pulsatile and is shaped by three main inputs: GHRH (stimulatory), somatostatin (inhibitory), and ghrelin (stimulatory). GH acts on the liver and other tissues to produce insulin-like growth factor 1 (IGF-1), which feeds back to the hypothalamus and pituitary. A GHRH analog works upstream of the pituitary: it binds the GHRH receptor on somatotroph cells and prompts the pituitary to release the GH it has stored. Researchers often emphasize that, because this route keeps the feedback loop intact, GH release remains subject to somatostatin and IGF-1 regulation, in contrast to exogenous GH, which bypasses the axis. That is a design rationale rather than a proven clinical advantage.
Structure and Design
- Native GHRH is a 44-amino-acid peptide. The first 29 residues retain the biological activity.
- Sermorelin is GHRH(1-29) amino-terminal fragment, the shortest sequence that keeps full activity. It is rapidly cleaved by dipeptidyl peptidase-IV (DPP-IV) and has a very short half-life, on the order of minutes (Walker, Clin Interv Aging 2006;1:307-308, discussing its pharmacology).
- Tesamorelin is a 44-amino-acid GHRH analog with a trans-3-hexenoyl group added to the N-terminal tyrosine. This modification protects against DPP-IV degradation while keeping receptor activity. It is approved in the United States for reduction of excess abdominal fat in HIV-infected adults with lipodystrophy (FDA approval 2010, marketed as Egrifta).
- CJC-1295 is a modified GHRH(1-29) analog. The form with a "drug affinity complex" (DAC) carries a reactive linker that binds covalently to circulating albumin, giving it a much longer half-life. The non-DAC version, often called modified GRF(1-29), has amino-acid substitutions for stability but a short duration of action.
Pharmacokinetics at a Glance
| Analog | Length | Stabilization strategy | Reported duration |
|---|---|---|---|
| Sermorelin | 29 aa | None (native fragment) | Very short (minutes) |
| Tesamorelin | 44 aa | N-terminal trans-3-hexenoyl group | Short; once-daily dosing in trials |
| CJC-1295 (no DAC) | 29 aa | Amino-acid substitutions | Short |
| CJC-1295 (with DAC) | 29 aa + linker | Albumin binding | Days (published half-life roughly a week) |
The Evidence Behind Each
Tesamorelin has the strongest evidence base. It was studied in randomized, placebo-controlled trials in HIV-associated abdominal fat accumulation, including Falutz et al. (N Engl J Med 2007;357:2359-2370) and Stanley et al. (JAMA 2014;312:380-389), the latter examining visceral and liver fat. These led to its regulatory approval for that narrow indication. Outside that indication, its use remains investigational.
Sermorelin was previously marketed in the United States as a diagnostic and treatment agent in pediatric GH deficiency and was later discontinued commercially for business reasons, not a published safety finding. Its literature is older, and much of it addresses diagnostic stimulation testing.
CJC-1295 with DAC was characterized in a human study by Teichman and colleagues, who reported that single and multiple doses produced prolonged, dose-related increases in GH and IGF-1 in healthy adults (J Clin Endocrinol Metab 2006;91:799-805). It is not an approved medicine, and the published human literature is limited in size and duration. The loss of GH pulsatility with a long-acting analog (a continuous "bleed" of GH-stimulating signal) is a recognized concern in the field and part of why shorter-acting analogs are often preferred for modeling physiological pulses in research.
Research Design Considerations
- Match the analog to the question. Studying acute pituitary responsiveness favors a short-acting analog; studying sustained receptor stimulation or downstream IGF-1 effects favors a long-acting one.
- Measure the right readouts. Pulsatile GH needs frequent sampling; IGF-1 is a slower integrated marker.
- Account for species differences. GHRH receptor pharmacology and DPP-IV activity differ between rodents and humans.
Regulatory Notes
Of the three, only tesamorelin is an FDA-approved product, for a single indication. Research-grade material is not the approved product.
Sources
- Falutz J, et al. Metabolic effects of a growth hormone-releasing factor in patients with HIV. N Engl J Med 2007;357:2359-2370.
- Stanley TL, et al. Effect of tesamorelin on visceral fat and liver fat in HIV-infected patients with abdominal fat accumulation: a randomized clinical trial. JAMA 2014;312:380-389. JAMA Network
- Teichman SL, et al. Prolonged stimulation of growth hormone (GH) and insulin-like growth factor I secretion by CJC-1295, a long-acting analog of GH-releasing hormone, in healthy adults. J Clin Endocrinol Metab 2006;91:799-805.
- Walker RF. Sermorelin: a better approach to management of adult-onset growth hormone insufficiency? Clin Interv Aging 2006;1:307-308.
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