The results of peptides acting on the growth hormone axis are measured with three kinds of measure: the IGF-1 level in the blood, body composition, meaning lean mass, fat mass and waist circumference, and simple tests of physical function. Research has used the same measures for forty years. Below is exactly what those studies measured, and which of those measures you can repeat yourself.
Three kinds of measure that come back in every study
The first measure is hormonal. Growth hormone is released in pulses, so a single blood measurement says little. That is why researchers measure IGF-1, insulin-like growth factor, which is produced in the liver under the influence of growth hormone and stays at a steady level through the day. It shows whether the axis responded at all.
The second measure is body composition: lean mass, fat mass and waist circumference. The third is physical function, measured with tests such as tandem walking or stair climbing. Together they give a picture that bathroom scales cannot, because scales show one number with no split between muscle and fat.
The 1990 study that started this discussion
That year the New England Journal of Medicine published a paper on growth hormone in men over sixty. The study took in 21 healthy men aged 61 to 81 whose IGF-1 level did not exceed 350 units per litre. Twelve of them received growth hormone subcutaneously three times a week for six months, and nine received nothing.
In the treated group IGF-1 rose into the range typical of young people, 500 to 1500 units per litre. Lean mass rose by 8.8 per cent, fat mass fell by 14.4 per cent, and lumbar spine density rose by 1.6 per cent. Skin thickness increased by 7.1 per cent, although that change did not reach statistical significance. In the untreated group none of these values changed.
What a secretagogue did in older people
In 2009 the Journal of Clinical Endocrinology and Metabolism described a study on capromorelin, an oral growth hormone secretagogue. It included 395 women and men aged 65 to 84 with mild functional limitation. Participants received one of four doses or placebo, and the study was planned for two years.
IGF-1 rose in every group receiving the drug, in proportion to the dose. After six months body weight rose by 1.4 kg, against a fall of 0.2 kg on placebo. Lean mass rose by 1.4 kg against 0.3 kg, and tandem walk time improved by 0.9 seconds. After a year stair climbing improved too. Fatigue, insomnia and a small rise in fasting glucose and glycated haemoglobin were also recorded, which shows that the metabolic measurement matters here as much as the functional one.
Tesamorelin and visceral fat
The most recent summary comes from 2026 and concerns tesamorelin, the only GHRH analogue approved as a medicine. The meta-analysis covered four randomised trials and a total of 909 patients with HIV-associated lipodystrophy. Tesamorelin at 2 mg reduced visceral fat and waist circumference, on average by 1.61 centimetres against placebo. The authors also noted more frequent discontinuation of treatment in the active group.
More about the molecule itself is in the guide to tesamorelin, and a map of the whole family in the guide to growth hormone peptides.
The measures side by side
| Measure | What it shows | How it was measured in the studies |
|---|---|---|
| IGF-1 from blood | whether the growth hormone axis responded | monthly, from a single draw |
| lean and fat mass | the direction of change in body composition | at the start and end of the period |
| waist circumference | the amount of fat around the abdomen | with a tape measure, at the same spot |
| tandem walk, stairs | physical function | a timed test every few months |
| glucose and glycated haemoglobin | the metabolic response | from blood, together with the other tests |
Which of these you can repeat yourself
IGF-1 is measured in an ordinary laboratory from a single blood draw, so it is a measure available outside a research study too. Waist circumference you can measure with a tape, always at the same spot and the same time of day. Record body weight in the morning, and take photos in the same light, otherwise a comparison after two months will show nothing.
Rhythm matters more than equipment. In the studies described, body composition was measured every few months, because changes of this kind take time. A week is too short to see anything, and daily weighing mainly shows fluctuations in body water.
Where this comparison ends
All the studies described above concern growth hormone or approved medicines, given to patients for defined indications. The peptides in our catalogue are sold as material for laboratory research and have no such human studies. The figures from these papers therefore describe the mechanism and the way of measuring, not a promised result. The status of each molecule is explained in the guide to the legal status of peptides.
It is also worth keeping in mind how long the molecule itself acts, because that decides when a measurement makes sense. Half-lives are gathered in the guide to how long a peptide stays in the body. Prices and availability for every item are on the price list, and the compounds are described in the shop.
Frequently asked questions
Why measure IGF-1 rather than growth hormone?
Growth hormone is released in pulses, so a single measurement says little. IGF-1 stays stable through the day and therefore serves as a marker of response.
How quickly do changes in body composition show?
In the studies described, body composition was measured after six and twelve months, because over a shorter time the differences are too small.
How large was the change in the 1990 study?
Lean mass rose by 8.8 per cent, fat mass fell by 14.4 per cent, and lumbar spine density rose by 1.6 per cent.
Does a secretagogue change metabolic results?
In the capromorelin study a small rise in fasting glucose and glycated haemoglobin was recorded, alongside improved body composition and function.
Do these figures apply to peptides from the shop?
No. They come from studies on growth hormone and approved medicines, while the peptides in the catalogue are sold as material for laboratory research.
Sources
- Rudman D, Feller AG, Nagraj HS et al. Effects of human growth hormone in men over 60 years old. New England Journal of Medicine, 1990, 323(1): 1-6. https://doi.org/10.1056/NEJM199007053230101
- White HK, Petrie CD, Landschulz W et al. Effects of an oral growth hormone secretagogue in older adults. Journal of Clinical Endocrinology and Metabolism, 2009, 94(4): 1198-1206. https://doi.org/10.1210/jc.2008-0632
- Ditta AM, Naeem RM, Sami MM et al. Efficacy and Safety of Tesamorelin in People Living With HIV (PLWH) With Lipodystrophy: A Systematic Review and Meta-Analysis. Journal of the International Association of Providers of AIDS Care, 2026, 25. https://doi.org/10.1177/23259582261475549