Growth hormone comes out of the pituitary in bursts, not a steady stream. A healthy young adult produces somewhere between 10 and 20 discrete pulses a day, with the largest arriving in the first few hours of slow wave sleep, and between pulses serum GH falls to near-undetectable. That pattern is not incidental. The liver, muscle and fat respond differently to pulsatile versus continuous GH exposure, and continuous elevation is associated with receptor downregulation and the metabolic problems seen in acromegaly. Everything sensible about secretagogue use follows from taking pulsatility seriously.

Two different levers

The pituitary somatotroph has two relevant receptors. The GHRH receptor responds to hypothalamic growth hormone releasing hormone and raises cyclic AMP, which drives synthesis and release. The GHS-R1a receptor responds to ghrelin, works through a different (phospholipase C, calcium) pathway, and additionally suppresses somatostatin, the brake that limits GH release. Because they are separate pathways, a GHRH analogue and a ghrelin mimetic given together produce a larger pulse than either alone. That synergy is the entire rationale behind the CJC plus ipamorelin pairing.

Tesamorelin

The only one of the three with FDA approval. Tesamorelin is a stabilised GHRH(1-44) analogue with a trans-3-hexenoyl group on the N terminus that resists DPP-4 degradation. It was approved in 2010 for HIV-associated lipodystrophy on the strength of two phase 3 trials with roughly 800 patients between them, dosed at 2 mg subcutaneously daily. Over 26 weeks visceral adipose tissue fell by about 15 to 18 percent versus placebo, measured by CT at the L4-L5 level, with IGF-1 rising around 80 percent. When treatment stopped, visceral fat came back. It has since been studied in non-HIV NAFLD populations with reductions in liver fat fraction.

Tesamorelin preserves pulsatility because it amplifies existing GHRH-driven pulses rather than overriding them. Its half life is short, around 30 minutes to 2 hours subcutaneously.

CJC-1295

Here the naming causes genuine confusion and it is worth being precise. CJC-1295 with DAC (drug affinity complex) carries a maleimidoproprionic acid linker that binds covalently to serum albumin, extending half life to roughly 6 to 8 days. That produces a sustained elevation of GH and IGF-1 lasting a week or more, sometimes called a bleed rather than a pulse. CJC-1295 without DAC is modified GRF(1-29), often sold as Mod GRF 1-29 or CJC-1295 no-DAC, with a half life of about 30 minutes. These are pharmacologically different drugs sold under nearly the same name.

The DAC version was studied by Teichman and colleagues in 2006 in healthy adults at 30 to 60 mcg per kg. Mean GH rose 2 to 10 fold for six days and IGF-1 rose 1.5 to 3 fold, sustained for 9 to 11 days. That paper is often cited as proof of efficacy, and it does demonstrate the pharmacology cleanly, but note what it also demonstrates: continuous rather than pulsatile elevation, which is precisely the pattern the physiology argues against. Development was later discontinued.

Ipamorelin

A pentapeptide ghrelin receptor agonist, notable mainly for what it does not do. Earlier GHRPs (GHRP-2, GHRP-6, hexarelin) raise cortisol, prolactin and ACTH at doses that release GH, and GHRP-6 in particular causes strong hunger. Ipamorelin at comparable GH-releasing doses does not meaningfully move cortisol or prolactin in the studies by Raun and colleagues that characterised it. Half life is roughly 2 hours. It went through phase 2 for postoperative ileus and was not carried forward.

Why timing matters

Somatostatin release from the hypothalamus oscillates. Give a secretagogue during a somatostatin trough and you get a large pulse; give it during a peak and you get a blunted one. In practice this pushes toward:

  • Dosing at least two hours after food, particularly after carbohydrate or fat, because insulin and free fatty acids both suppress GH release
  • A dose immediately before sleep, to ride with rather than against the natural nocturnal pulse
  • Leaving three or more hours between doses so the pituitary is not continuously stimulated

Common practical ranges are 100 mcg ipamorelin and 100 mcg Mod GRF 1-29 per dose, one to three times daily, and 1 to 2 mg per week of CJC-1295 with DAC. Tesamorelin protocols follow the label at 1.4 to 2 mg daily. These are not from dose-finding trials in healthy people wanting body composition change, because those trials do not exist.

Measure IGF-1 rather than GH

A single serum GH reading is close to useless because of the pulsatility. Draw at the wrong minute and a well-responding person looks like a non-responder. IGF-1, produced mainly by the liver in response to GH, has a half life of about 12 to 15 hours bound to IGFBP-3 and integrates GH exposure over roughly a day, so it is the practical readout. Get a baseline before starting and repeat at six to eight weeks, and interpret against an age-adjusted reference range rather than an absolute number.

Side effects and honest limits

Water retention, numbness or tingling in the hands, joint aches and reduced insulin sensitivity all scale with IGF-1 elevation and are the same effects seen with exogenous GH. Injection site flushing is common with GHRH analogues. Fasting glucose and HbA1c are worth monitoring if you run a course for more than a couple of months.

The evidence gap is specific: tesamorelin has solid randomised data for visceral fat in a defined patient population. There is no comparable trial evidence that any of these three improves lean mass, strength, recovery or body composition in healthy trained adults. Elevated IGF-1 is a biomarker rather than an outcome.