Gabriel Alizaidy, MD, MS
Gabriel Alizaidy, MD, MS
Published Apr 23, 2025
The idea that sermorelin needs to be cycled is not just outdated; it was never clinically valid to begin with.
I recently watched a lecture from a well-known compounding pharmacy about the benefits of sermorelin and how healthcare providers can better utilize this peptide in their practice. It was pretty solid for the most part. The speaker explained how sermorelin is a synthetic analog of growth hormone-releasing hormone (GHRH) that stimulates the pituitary gland to release endogenous growth hormone (GH) in short, physiologic pulses. This mirrors how the body naturally operates, using tightly regulated feedback mechanisms like somatostatin to prevent overstimulation. Unlike recombinant human growth hormone (rhGH), sermorelin does not override this system. It works within it.
They also highlighted the benefits of increased IGF-1, which plays a central role in muscle growth, fat metabolism, recovery, and cognitive function. Raising IGF-1 through pituitary-driven GH release allows the body to reap these benefits without pushing GH or IGF-1 to supraphysiologic levels.
But toward the end of the talk, when the discussion shifted towards dosing, the speaker clearly and confidently stated that sermorelin should be cycled. That's where they lost me.
Cycling sermorelin comes from a misunderstanding of its pharmacology, often reinforced by old habits from bodybuilding forums where 5:2 (5 days on: 2 days off) dosing schedules were more about saving money than improving outcomes. With rhGH, the problem is not just constant exposure. It is the non-physiologic delivery that leads to abrupt spikes in GH levels, detached from the body's natural rhythm. Exogenous GH bypasses the hypothalamic-pituitary axis and delivers hormone in a flat, prolonged pattern known as square wave physiology. This disrupts normal feedback, causes GH levels to stay elevated for hours, and alters how tissues respond to the hormone. Over time, this may lead to downregulation of GH receptors, impaired signaling, and diminished therapeutic effect. For this reason, some providers suggest cycling, or taking breaks, to reset somatotroph sensitization.
An editorial published in Clinical Interventions in Aging explains why sermorelin avoids the issues seen with exogenous GH. It works through the body’s native signaling pathway, triggering short, self-regulated pulses of GH that preserve normal feedback. GH is released episodically, not continuously. This avoids square wave exposure (see image below), where hormone levels stay elevated for extended periods in a flat, unnatural pattern. That kind of exposure overrides normal feedback and contributes to receptor downregulation. In contrast, sermorelin allows the pituitary to continue functioning as intended.
Don't be a square (wave): sermorelin supports natural growth hormone rhythms.
The data are clear. In a study using 14 days of continuous intravenous infusion of GHRH in healthy men and a GH-deficient child, pulsatile GH release persisted, IGF-1 levels increased, and pituitary responsiveness remained intact. There was no desensitization, no depletion, and no loss of function.
An 8-day continuous subcutaneous infusion study confirmed the same. GH pulse frequency and amplitude increased. The GH reservoir remained available. Even high infusion doses produced no signs of pituitary fatigue. These studies used round-the-clock infusion. And yet the pituitary still responded.
Now compare that to how sermorelin is actually used. A single subcutaneous injection once per day, with a plasma half-life of 10 to 20 minutes. Exposure is brief, self-limited, and cleared within the hour. This creates a short signal to the pituitary, which then initiates GH release under full physiological control. It is nothing like administering rhGH.
Sermorelin was originally approved for children with growth hormone deficiency and prescribed as a daily injection. Not cycled. Clinical trials showed improved growth, increased IGF-1, and preserved pituitary function with long-term daily use.
There is no mechanistic or clinical rationale for taking breaks. Cycling sermorelin is a solution to a problem that does not exist. It comes from treating sermorelin like rhGH, when their actions could not be more different.
If the goal is to optimize GH in a physiologic and sustainable way, daily sermorelin use is the standard. That is what the science supports.
References
Vance ML, Kaiser DL, Martha PM Jr, Furlanetto R, Rivier J, Vale W, Thorner MO. (1989). Lack of in vivo somatotroph desensitization or depletion after 14 days of continuous GHRH administration in normal men and a GH-deficient boy. J Clin Endocrinol Metab, 68(1), 22–28. https://doi.org/10.1210/jcem-68-1-22 Brain C, Hindmarsh PC, Brook CGD, Matthews DR. (1988). Continuous subcutaneous GHRH analogue augments GH secretion with no desensitization of the somatotroph. Clin Endocrinol, 28(5), 543–549. https://doi.org/10.1111/j.1365-2265.1988.tb03689.x Walker RF. (2006). Sermorelin: A better approach to management of adult-onset GH insufficiency? Clin Interv Aging, 1(4), 307–308. https://doi.org/10.2147/ciia.2006.1.4.307 Geref (sermorelin acetate for injection) prescribing information. (n.d.). Retrieved from https://worldhealth.net/news/geref_seristim/
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