A sentence that starts with "a study confirmed" can mean very different things. Sometimes it stands for seven volunteers and one night in a laboratory, sometimes two thousand patients and a year of follow-up, and sometimes a mouse missing one protein. Below are six things to check in every such sentence, with examples from studies cited on this site.
First: who took part
The most important split is between humans, animals and cell cultures. A result from an isolated heart describes an isolated heart and nothing more. A paper on hexarelin in Circulation Research from 2002 showed an action through the CD36 protein in perfused hearts and in mice. The molecule as a whole is described in the guide to hexarelin, but no conclusion about its action in humans follows from that paper.
For part of our range the data come only from animals, and we say so plainly. That is the case with MOTS-c and SLU-PP-332, as the MOTS-c page shows.
Second: how many people
Hormone studies with sleep recordings are usually run on groups of seven. That was the size of the studies on ghrelin from 2003, on hexarelin from 2004 and on GHRP-2 from 1998. A group of that size can detect a large change, but not a moderate one.
At the other end are registration trials for medicines, run on thousands of people over many months. The difference is clear when you compare the weight loss peptides gathered in the guide to semaglutide, tirzepatide and retatrutide.
Third: how the substance was given
The route of administration changes the result enough to be a study topic of its own. GHRP-6 worked when given into the nose and did not work when swallowed, even though the oral dose was ten times larger. This is covered in the guide to peptide routes of administration.
In the sleep studies administration was intravenous, in hospital, over several hours. Figures from such a protocol do not describe a vial dissolved at home, and that is the honest limit of how they can be used.
Fourth: how long it lasted
One night, four weeks and a year give three different kinds of knowledge. The CJC-1295 study from 2006 ran for 28 and 49 days in two parts, with rising doses and a placebo group. That is why it can give a half-life and the length of time IGF-1 stayed above baseline.
A short protocol says nothing about the effects of longer use. Time figures for the whole catalogue are gathered in the guide to peptide half-lives.
Fifth: what exactly was measured
A hormone in the blood is not the same as the result someone is after. A rise in growth hormone after an injection is a substitute marker, not muscle gain or faster healing. Such a marker is called a surrogate endpoint, and it is often mistaken for the goal.
| What the text says | What stands behind it |
|---|---|
| Raised growth hormone | a blood concentration measurement, usually over one day |
| Raised IGF-1 | an indirect measurement, reflecting longer action of the axis |
| Reduced body weight by so many per cent | a clinical outcome, requiring a long study with a placebo group |
| Sped up healing in a rat | an animal model, with no direct translation to humans |
Sixth: was the difference significant
In scientific writing you will meet two different phrasings. Statistically significant means the difference from placebo cannot be explained by chance. A tendency or trend means the result pointed one way but did not cross the significance threshold.
The 1999 GHRP-6 study has both kinds of result at once. After nasal administration the rise in growth hormone was significant, while the rise in ACTH was only noted as a trend. A seller who gives both with one word wipes out the whole difference.
How we apply this on this site
For every number we try to say where it comes from: the journal, the year and who the study was done on. Where there are no human data, we say there are none instead of reaching for animal results. That applies to items that sell well too, because the truth about the state of research does not depend on what happens to be in the basket.
All compounds are sold as material for laboratory research, and we give no protocols of use with them. The reasons are explained in the guide to the legal status of peptides, and the full catalogue with prices is on the price list.
Frequently asked questions
Can a result from rats be applied to humans?
Not directly. An animal model points the direction for research, not the action in humans.
Why do peptide studies include so few people?
Protocols with hormone measurements and EEG recordings are expensive. A group of seven is typical for them.
What is a surrogate marker?
An indirect measurement, such as a hormone concentration, used in place of the outcome that really matters.
How does a trend differ from a significant result?
A trend did not cross the threshold of statistical significance, so it may be down to chance.
Where can I check the sources of the figures in your guides?
We give the journal and the year in the text. With those you can find the paper in scientific publication databases.
Sources
- Bodart V, Febbraio M, Demers A et al. CD36 mediates the cardiovascular action of growth hormone-releasing peptides in the heart. Circulation Research, 2002, 90(8): 844-849. https://doi.org/10.1161/01.res.0000016164.02525.b4
- Weikel JC, Wichniak A, Ising M et al. Ghrelin promotes slow-wave sleep in humans. American Journal of Physiology - Endocrinology and Metabolism, 2003, 284(2): E407-E415. https://doi.org/10.1152/ajpendo.00184.2002
- Frieboes RM, Antonijevic IA, Held K et al. Hexarelin decreases slow-wave sleep and stimulates the secretion of GH, ACTH, cortisol and prolactin during sleep in healthy volunteers. Psychoneuroendocrinology, 2004, 29(7): 851-860. https://doi.org/10.1016/S0306-4530(03)00152-5
- Moreno-Reyes R, Kerkhofs M, L'Hermite-Balériaux M et al. Evidence against a role for the growth hormone-releasing peptide axis in human slow-wave sleep regulation. American Journal of Physiology, 1998, 274(5): E779-E784. https://doi.org/10.1152/ajpendo.1998.274.5.E779
- Teichman SL, Neale A, Lawrence B et al. Prolonged stimulation of growth hormone (GH) and insulin-like growth factor I secretion by CJC-1295, a long-acting analog of GH-releasing hormone, in healthy adults. Journal of Clinical Endocrinology and Metabolism, 2006, 91(3): 799-805. https://doi.org/10.1210/jc.2005-1536
- Frieboes RM, Murck H, Antonijevic IA, Steiger A. Effects of growth hormone-releasing peptide-6 on the nocturnal secretion of GH, ACTH and cortisol and on the sleep EEG in man: role of routes of administration. Journal of Neuroendocrinology, 1999, 11(6): 473-478. https://doi.org/10.1046/j.1365-2826.1999.00364.x