Sermorelin, Growth Hormone, and the Slow Decline of the Somatotropic Axis

Men in their fifties and sixties ask me about sermorelin more than any other peptide, often after an anti-aging clinic told them their growth hormone was low and that a nightly injection would hand back the body they had at thirty. They want to know whether any of that is true, and the answer takes a while to assemble, because sermorelin sits in an unusual place where the physiology is solid, the marketing is loud, and the human trials are small and mostly thirty years old.

How your growth hormone axis works

Growth hormone doesn't trickle out steadily, and the rhythm explains everything that follows. Your hypothalamus releases growth hormone releasing hormone, or GHRH, a peptide that travels a short distance to the anterior pituitary and tells the somatotroph cells there to fire off a burst of growth hormone. Those bursts come in pulses, and the largest of them arrive during deep slow-wave sleep, the heaviest stage of non-dreaming sleep. Growth hormone then reaches the liver, which answers by making insulin-like growth factor 1, or IGF-1, the messenger that carries out much of what we credit to growth hormone and the number your physician measures because it holds steady between pulses. Two other signals shape the rhythm, since somatostatin acts as the brake that shuts a pulse down and keeps the system self-limiting, while ghrelin, the stomach peptide that rises when you're hungry, acts as a second accelerator through its own receptor on the pituitary.

The whole system winds down with age. Iranmanesh and colleagues, sampling blood every 10 minutes for 24 hours in 21 healthy men aged 21 to 71, calculated that each decade of adult age cut the daily growth hormone production rate by about 14 percent, and that each single unit of body mass index knocked off another 6 percent [1]. Clinicians sometimes call that drift the somatopause. Sleep tracks it closely, and in a pooled analysis of 149 healthy men aged 16 to 83, Van Cauter and colleagues found that deep slow-wave sleep fell from 18.9 percent in early adulthood to 3.4 percent by midlife, with growth hormone secretion falling in parallel and the association holding independently of age [2]. This means a man of 50 has already lost most of the deep sleep that used to drive his largest nightly pulse.

What sermorelin is, and where it came from

Sermorelin is GHRH(1-29), the first 29 amino acids of your own growth hormone releasing hormone and, as Prakash and Goa described in their 1999 review, the shortest synthetic fragment that keeps the full biological activity of the natural hormone [3]. Given under the skin, it stimulates growth hormone release from the anterior pituitary and nothing else. The FDA approved it in 1997 as Geref for children with growth hormone deficiency, where a nightly subcutaneous dose of 30 micrograms per kilogram increased height velocity over 12 months in some children, though less than daily somatropin did [3]. The manufacturer later withdrew it, not for harm but because it couldn't compete commercially with recombinant growth hormone [4]. Every sermorelin prescription written in the United States today is compounded, which means it isn't FDA-approved, and its FDA-approved relative is recombinant growth hormone itself.

Why prompt the gland instead of replacing the hormone

The case for a secretagogue, a drug that prompts your own gland to secrete rather than supplying the finished hormone, rests on where the feedback sits. Inject growth hormone and you bypass the pituitary, so the dose you chose is the exposure your tissues get, at a level no pulse generator regulates. Stimulate with GHRH instead and the pituitary still answers to somatostatin, so release stays episodic and self-limiting and an overdose is difficult to produce [4]. My read is that this argument is real physiology rather than marketing, and it's also the reason sermorelin can never do what growth hormone does at high dose, since a self-limiting system is by definition a weaker lever.

What the human trials in older adults found

Three small trials carry most of the weight here, and they found consistent hormonal changes with inconsistent effects on how people function. Corpas and colleagues gave 10 healthy old men GHRH(1-29) twice daily for 14 days at 0.5 mg and again at 1 mg, and at the higher dose their 24-hour growth hormone output and IGF-1 rose until they matched those of healthy young men [5]. Khorram and colleagues ran the longest trial, a placebo-controlled study of nightly GHRH analog injections at 10 micrograms per kilogram for 16 weeks in 10 women and 9 men aged 55 to 71. They found higher nocturnal growth hormone, IGF-1 that rose within 2 weeks but drifted back toward baseline by 16 weeks, and greater skin thickness in both sexes. Lean body mass, insulin sensitivity, well-being, and libido increased in the men only, with transient hyperlipidemia as the sole side effect [6]. Vittone and colleagues took 11 healthy men aged 64 to 76 with low IGF-1 and gave 2 mg of GHRH(1-29) nightly for 6 weeks, which raised nocturnal growth hormone release yet left IGF-1 unchanged, improved 2 of 6 strength measures, and produced no change in body composition, glucose, or lipids [7].

What those trials don't contain matters as much as what they do, since nobody measured whether these men fell less often, lived longer, or avoided a single disease.

The cautionary story of growth hormone itself

The enthusiasm for all of this traces back to one 1990 trial. Rudman and colleagues gave recombinant growth hormone to 12 healthy men aged 61 to 81 for six months and measured an 8.8 percent rise in lean body mass, a 14.4 percent fall in fat mass, and a 1.6 percent gain in lumbar bone density against 9 untreated controls [8]. That paper launched an industry, and the follow-up was less kind. Liu and colleagues pooled 18 randomized study populations of growth hormone in healthy older adults for a 2007 systematic review in the Annals of Internal Medicine, and found a 2.1 kg decrease in fat mass and a 2.1 kg increase in lean mass with no change in body weight. The treated groups also had significantly more soft tissue edema, joint pain, carpal tunnel syndrome, and gynecomastia, along with a higher rate of new diabetes and impaired fasting glucose [9]. Their conclusion was that growth hormone can't be recommended as an antiaging therapy, and I agree with it.

What remains unknown, and who shouldn't use it

No trial has tested whether sermorelin extends life, prevents disease, or preserves independence, and the largest published study ran only 16 weeks in 19 people. The theoretical worry is cancer, since IGF-1 drives cell growth and survival. Renehan and colleagues, in a meta-regression of 21 studies covering 3,609 cancer cases, found higher circulating IGF-1 associated with prostate cancer and premenopausal breast cancer, with odds ratios near 1.5 comparing the 75th with the 25th percentile [10]. Those are observational associations at natural IGF-1 levels rather than evidence that a peptide causes cancer, though they're reason enough that we don't offer any growth hormone secretagogue to a person with an active malignancy, and we don't use it in pregnancy or in anyone whose glucose is already drifting upward.

What to do

Everything that raises your own growth hormone output carries more evidence than the injection does, and all of it is unglamorous. Protect deep sleep first, because slow-wave sleep is where your largest pulse lives and losing it tracks the hormonal decline directly [2]. Lift heavy things on a schedule, since resistance training builds the lean mass that people hope a peptide will give them, and it does so with decades of trial evidence behind it. Then go after the two variables that suppress the axis hardest, visceral fat and fasting insulin, because adiposity alone cut daily growth hormone secretion by 6 percent per body mass index unit [1]. I've written separately on how sleep drives your mitochondria.

When we do use sermorelin, we use it in someone who has already fixed sleep, training, and insulin, who understands that the evidence supports a rise in growth hormone and IGF-1 rather than a longer life, and who wants labs followed while they try it. Anyone selling it as an anti-aging cure is ahead of the data by about three decades.

Ask a provider about sermorelin

References

1. 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. J Clin Endocrinol Metab. 1991. PMID: 1939523
2. Van Cauter E, Leproult R, Plat L. Age-related changes in slow wave sleep and REM sleep and relationship with growth hormone and cortisol levels in healthy men. JAMA. 2000. PMID: 10938176
3. Prakash A, Goa KL. Sermorelin: a review of its use in the diagnosis and treatment of children with idiopathic growth hormone deficiency. BioDrugs. 1999. PMID: 18031173
4. Walker RF. Sermorelin: a better approach to management of adult-onset growth hormone insufficiency? Clin Interv Aging. 2006. PMID: 18046908
5. Corpas E, Harman SM, Piñeyro MA, et al. Growth hormone (GH)-releasing hormone-(1-29) twice daily reverses the decreased GH and insulin-like growth factor-I levels in old men. J Clin Endocrinol Metab. 1992. PMID: 1379256
6. Khorram O, Laughlin GA, Yen SS. Endocrine and metabolic effects of long-term administration of [Nle27]growth hormone-releasing hormone-(1-29)-NH2 in age-advanced men and women. J Clin Endocrinol Metab. 1997. PMID: 9141536
7. Vittone J, Blackman MR, Busby-Whitehead J, et al. Effects of single nightly injections of growth hormone-releasing hormone (GHRH 1-29) in healthy elderly men. Metabolism. 1997. PMID: 9005976
8. Rudman D, Feller AG, Nagraj HS, et al. Effects of human growth hormone in men over 60 years old. N Engl J Med. 1990. PMID: 2355952
9. Liu H, Bravata DM, Olkin I, et al. Systematic review: the safety and efficacy of growth hormone in the healthy elderly. Ann Intern Med. 2007. PMID: 17227934
10. Renehan AG, Zwahlen M, Minder C, et al. Insulin-like growth factor (IGF)-I, IGF binding protein-3, and cancer risk: systematic review and meta-regression analysis. Lancet. 2004. PMID: 15110491