# Three compounds, one axis, three very different distances from proof

> Compare Ipamorelin, CJC-1295 and Tesamorelin — Growth Hormone Axis Research Peptides — steroidnpeptides — A side-by-side reading of three Growth Hormone Axis research peptides: which receptor each acts on, what its strongest human study actually measured, how long each one lasts, and how far apart their evidence bases really are.

**SIDE BY SIDE**

Two receptors, half-lives spanning three orders of magnitude, and one approval between them. The differences that matter are not the ones the marketing emphasises.

## The short version

All three compounds on this desk end up doing the same thing: making the pituitary gland release more of the body's own growth hormone. They get there two different ways.

Ipamorelin uses the *ghrelin receptor* — the one the hunger hormone acts on. CJC-1295 and tesamorelin use the receptor for *growth-hormone-releasing hormone*, the brain's own signal. Same destination, different doors.

The bigger difference is how long each one lasts. Ipamorelin is measured in hours [4]. CJC-1295's long-acting form is measured in days [9]. Tesamorelin was given daily in its trials [15][17].

The biggest difference of all is evidence. Tesamorelin has an approval and a 52-week trial programme behind it [14][17]. CJC-1295 has a few early studies of hormone levels. Ipamorelin has one human trial that did not work [3]. Those three positions are not close together, and no summary that lists the compounds as a menu of similar options is being honest about them.

## Two receptors, one hormone

The growth hormone axis has two natural upstream inputs to pituitary somatotroph cells. Growth-hormone-releasing hormone from the hypothalamus is one; ghrelin, acting at the GHS-R1a receptor, is the other. The compounds here divide cleanly along that line.

CJC-1295 and tesamorelin are both engineered analogues of growth-hormone-releasing hormone, and both exist because the native hormone is destroyed within minutes by dipeptidyl peptidase-IV. They solve that problem differently. Tesamorelin attaches a trans-3-hexenoic acid group to the N-terminus. CJC-1295 substitutes four residues internally and, in its long-acting DAC form, adds a linker that bonds covalently to circulating albumin — an approach demonstrated in rats to give a four-fold increase in growth hormone area-under-curve over the unconjugated peptide, with the compound detectable in plasma beyond 72 hours [12].

Ipamorelin sits on the other input entirely. It is a selective GHS-R1a agonist, and its defining property is what it leaves alone: unlike the earlier growth-hormone-releasing peptides, it does not meaningfully raise ACTH, cortisol or prolactin.

That the two pathways are separate and converge on the same cell is genuine pharmacology, and it is the reason a GHRH analog and a ghrelin-receptor agonist are so often discussed as a pair. What does not exist is a trial of that pair. The combination rests entirely on single-agent data for each half.

## What each one was actually studied for

| Compound | Receptor target | Strongest human evidence | What that study measured | Regulatory status |
|---|---|---|---|---|
| Ipamorelin | Ghrelin receptor, GHS-R1a | One Phase 2 RCT, 114 adults [3] | Time to first tolerated meal after bowel resection — endpoint missed [3] | Not approved anywhere; research chemical |
| CJC-1295 | GHRH receptor | Early pharmacology in healthy adults [9][10] | Plasma growth hormone and IGF-1 concentrations over days [9][10] | Not approved; original programme discontinued |
| Tesamorelin | GHRH receptor | Five pooled RCTs [13]; 52-week programme, 273 participants [17] | Visceral adipose tissue in square centimetres [13][15][17] | Approved in the US in 2010, HIV-associated lipodystrophy only [14] |

Read the fourth column rather than the first. The compounds differ far less in what they do to the pituitary than in what anybody has bothered to measure afterwards, and the fourth column is the only one that records that.

## Evidence maturity, ranked honestly

**Tesamorelin.** Five randomised controlled trials pooled in a 2026 meta-analysis, showing a visceral-fat reduction of 27.71 square centimetres (95% CI -38.37 to -17.06), trunk fat down 1.18 kilograms, hepatic fat fraction down 4.28 percentage points and lean body mass up 1.42 kilograms, all at p<0.001 and without serious adverse events [13]. A six-month *JAMA* trial in 50 adults with a -42 square centimetre treatment effect (p=0.005) and a net hepatic fat reduction of 2.9 percentage points (p=0.003) [15]. A 52-week programme in 273 participants against 137 on placebo, sustaining an 18% visceral-fat reduction (p<0.001 against baseline) [17]. This is what a mature evidence base looks like.

**CJC-1295.** Three small human studies. Dose-dependent two- to ten-fold growth hormone elevation for six days or more, IGF-1 up one-and-a-half to three-fold for nine to eleven days, half-life 5.8 to 8.1 days [9]. Pulsatility preserved, basal growth hormone up roughly 7.5-fold, mean growth hormone up about 46%, IGF-1 up about 45% at one week [10]. A serum proteomic signature in 11 men that tracks IGF-1 [8]. Every endpoint is a laboratory measurement of the axis itself. None is a clinical outcome.

**Ipamorelin.** One Phase 2 trial in 114 patients that missed its primary endpoint at 25.3 hours against 32.6 on placebo, p=0.15 [3]. One pharmacokinetic study, eight volunteers per dose level, half-life about 2 hours, a single growth hormone pulse peaking near 40 minutes [4]. The remainder is animal work: bone growth rising from 42 to 52 micrometres per day in rats [5], and a 24% reduction in chemotherapy-associated weight loss in ferrets [1]. There is also a 28-day rat study of a different GHS-R1a agonist showing dose-dependent myocardial degeneration, which is a class-level warning rather than an ipamorelin finding [2].

The ordering is not a ranking of usefulness or of interest. It is a ranking of how much has actually been measured.

## Duration is the practical difference

The three compounds differ in duration by roughly three orders of magnitude, and duration governs nearly everything else about how they behave.

Ipamorelin's terminal half-life in humans is approximately 2 hours, with clearance of 0.078 litres per hour per kilogram and a steady-state volume of distribution of 0.22 litres per kilogram. The growth hormone response arrives as one discrete pulse peaking around 40 minutes after administration [4]. Exposure is brief by design.

CJC-1295 in its DAC form has an estimated half-life of 5.8 to 8.1 days, keeps growth hormone elevated for six days or more after a single dose, and holds IGF-1 above baseline for nine to eleven days after one dose and up to 28 days after several [9]. It is worth restating that the no-DAC form sold under the same name behaves nothing like this.

Tesamorelin sits between them in practice. It was administered daily at 2 milligrams throughout its trial programme [15][17], which implies an exposure profile requiring daily replacement rather than one lasting for days.

Duration is also the axis along which the reported downsides sort themselves. Fluid retention, glycaemic drift and cumulative IGF-1 exposure all track sustained elevation rather than transient pulses, which is why community accounts consistently describe the long-acting form as the one that produces more of them.

## What none of them was studied for

Not one study in the reference list on this desk enrolled healthy, trained adults to measure strength, hypertrophy or body-composition change in that population. That sentence is worth reading twice, because the entire popular framing of these compounds assumes the opposite.

The lean-mass number that circulates most widely — an increase of 1.42 kilograms — comes from a pooled analysis of randomised trials in adults with HIV-associated lipodystrophy who were being treated for fat redistribution [13]. It is a real result in a real population, and that population is not the one doing the searching.

Ipamorelin's body-composition-adjacent data are a rat bone-growth experiment measuring micrometres per day [5] and a ferret study of chemotherapy weight loss [1]. CJC-1295's human data end at hormone concentrations and a proteomic signature [8][9][10]. There is no head-to-head trial of any two of these three compounds against each other, and the combination protocol discussed most often online has never been trialled for any outcome at all.

This desk also does not cover anabolic-androgenic steroids, which are a controlled-substance class, and does not present any compound here as an alternative to, a substitute for, or a component of anything in that category. All three compounds are prohibited in sport at all times under category S2 of the World Anti-Doping Agency list; CJC-1295 has been identified by mass spectrometry in a preparation seized in an anti-doping context [7]. Those are facts about the compounds, recorded here because they are part of the published picture.

## The one place with comparable human numbers

Glucose handling is the single question on which the three compounds can almost be compared directly, and even there the data are lopsided.

Tesamorelin has the cleanest record. Two weeks of 2 milligrams daily in 13 healthy men raised mean overnight growth hormone by 0.5 micrograms per litre (p=0.004) and IGF-1 by 181 micrograms per litre (p<0.0001), while fasting glucose (p=0.93) and insulin-stimulated glucose uptake (p=0.61) were both unchanged [16]. Over 52 weeks in the patient population, glucose changes were not clinically significant [17].

For CJC-1295 and ipamorelin, no equivalent controlled human glycaemic dataset exists. What can be said is mechanistic: growth hormone is glucose-sparing and reduces peripheral insulin sensitivity when sustained, and ipamorelin has an additional growth-hormone-independent insulinotropic action on pancreatic islet tissue in ex vivo preparations. Those two influences pull in opposite directions, and nobody has measured where they land in a person.

The asymmetry is the lesson. One compound has been through the studies that would answer the question. The other two have not, and the absence of a finding is not the same as a reassuring one.

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A reference desk on the growth hormone axis: it reports what the trials measured and names the species they measured it in, and it covers neither anabolic pharmacology nor any way of obtaining anything.