Understanding GHRH Analogs

Growth hormone-releasing hormone (GHRH) analogs are synthetic peptides that bind the GHRH receptor on pituitary somatotroph cells, prompting the release of endogenous growth hormone (GH). Three analogs dominate the published literature: Sermorelin, CJC-1295, and Tesamorelin. All three engage the same receptor, but they differ sharply in structure, half-life, and the shape of the GH pulse they produce.

Sermorelin (GRF 1-29)

Sermorelin is a truncated 29-amino-acid fragment of native GHRH and the shortest sequence that retains full biological activity. Its plasma half-life is roughly 10–20 minutes, which closely mimics the body's natural pulsatile GH release. Because clearance is rapid, downstream negative feedback from IGF-1 and somatostatin remains intact, preserving physiologic rhythm.

CJC-1295

CJC-1295 is modified GRF 1-29 with four amino-acid substitutions that resist enzymatic degradation. It exists in two forms. CJC-1295 without DAC (Modified GRF 1-29) has a half-life of about 30 minutes and produces discrete GH pulses similar to Sermorelin. CJC-1295 with DAC adds a Drug Affinity Complex that binds serum albumin, extending the half-life to roughly 5–8 days. The pharmacokinetic study by Teichman et al. (2006) reported sustained 2- to 10-fold GH elevations and 1.5- to 3-fold IGF-1 elevations from a single dose, but this produces a continuous "GH bleed" rather than physiologic pulses.

Tesamorelin

Tesamorelin is a stabilized GHRH(1-44) analog with an N-terminal trans-3-hexenoic acid group that resists dipeptidyl peptidase-IV cleavage. Its half-life is roughly 26–38 minutes in HIV-infected adults. It is the only GHRH analog in this group with FDA approval, indicated for the reduction of excess visceral adipose tissue in HIV-associated lipodystrophy, supported by randomized controlled trials published in NEJM (Falutz et al., 2007) and JAIDS.

Pulse Modulation at a Glance

• Sermorelin & CJC-1295 (no DAC): short pulses, preserved feedback, physiologic profile.
• CJC-1295 with DAC: sustained elevation, blunted pulsatility, weekly dosing in research models.
• Tesamorelin: short half-life with daily dosing, robust IGF-1 response, best-characterized clinical profile.

References

• Teichman SL, et al. Prolonged stimulation of GH and IGF-1 secretion by CJC-1295. J Clin Endocrinol Metab. 2006;91(3):799–805.
• Falutz J, et al. Metabolic effects of tesamorelin in HIV lipodystrophy. N Engl J Med. 2007;357:2359–2370.
• Walker RF. Sermorelin: a better approach to management of adult-onset GH insufficiency? Clin Interv Aging. 2006;1(4):307–308.