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# Read a little further.

We gather the studies and regulatory sources used in these pages, with a note on the kind of question each can address.

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## Different sources answer different questions.

The age-related measurements explain why these four signals draw attention. They do not establish that administering the matching option changes the course of aging. A paper about a precursor is not a trial of NAD+ itself, and a study of free GHK is not automatically a study of GHK-Cu.

The FDA material concerns regulatory status and the limits of available evidence. It cannot supply a missing clinical result.

- [NAD+ and aging cells](https://pubmed.ncbi.nlm.nih.gov/24360282/) 2013 · Tissue NAD+ and cellular communication in aging research, including mechanistic work in mice. DOI: 10.1016/j.cell.2013.11.037

- [An early NAD+ infusion study](https://pubmed.ncbi.nlm.nih.gov/31572171/) 2019 · A small exploratory human infusion study measuring blood and urine metabolites, rather than long-term aging outcomes. DOI: 10.3389/fnagi.2019.00257

- [A controlled oral precursor study](https://pubmed.ncbi.nlm.nih.gov/29599478/) 2018 · A controlled human study of oral nicotinamide riboside, which is a precursor rather than direct NAD+ treatment. DOI: 10.1038/s41467-018-03421-7

- [MOTS-c in aging men](https://pubmed.ncbi.nlm.nih.gov/32182209/) 2020 · Observational measurements in healthy men, with different age patterns in blood and muscle. DOI: 10.18632/aging.102944

- [MOTS-c in exercise and mouse research](https://pubmed.ncbi.nlm.nih.gov/33473109/) 2021 · Research on the natural exercise signal alongside experiments administering MOTS-c to mice of different ages. DOI: 10.1038/s41467-020-20790-0

- [FDA’s MOTS-c evidence assessment](https://www.fda.gov/media/193347/download) 2026 · FDA staff’s review of the available MOTS-c evidence, including substantial human and animal safety gaps. https://www.fda.gov/media/193347/download

- [Growth-hormone signaling in older men](https://pubmed.ncbi.nlm.nih.gov/10522985/) 1999 · Human research investigating GHRH signaling and age-related differences in nighttime growth-hormone output. DOI: 10.1210/jcem.84.10.6063

- [GHRH in a small older-adult study](https://pubmed.ncbi.nlm.nih.gov/1379256/) 1992 · A small study measuring growth hormone and IGF-1 responses in older men, without establishing longevity benefit. DOI: 10.1210/jcem.75.2.1379256

- [FDA’s determination on former sermorelin products](https://www.federalregister.gov/d/2013-04827) 2013 · The FDA determination distinguishes the former products’ withdrawal from a withdrawal for safety or effectiveness reasons. https://www.federalregister.gov/d/2013-04827

- [FDA guidance on patient-specific compounding](https://www.fda.gov/media/174456/download) 2025 · FDA guidance relevant to components of previously approved drugs and patient-specific pharmacy preparation. https://www.fda.gov/media/174456/download

- [GHK, aging and preclinical research](https://pmc.ncbi.nlm.nih.gov/articles/PMC8789089/) 2020 · A review connecting the plasma GHK age observation with cell and animal research; it is not a human injection trial. DOI: 10.31491/apt.2020.03.014

- [GHK and gene activity in lung cells](https://pubmed.ncbi.nlm.nih.gov/22937864/) 2012 · Research involving free GHK and human lung cells, distinct from clinical treatment with GHK-Cu. DOI: 10.1186/gm367

- [FDA’s peptide safety concerns](https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks) 2026 · FDA’s safety concerns and withdrawn-nomination entries; the page identifies April 22, 2026 as its current date. https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks

- [FDA’s cosmetic and drug distinction](https://www.fda.gov/cosmetics/cosmetic-products/wrinkle-treatments-and-other-anti-aging-products) 2022 · FDA’s explanation of when intended use places an anti-aging product under drug rules rather than cosmetic rules. https://www.fda.gov/cosmetics/cosmetic-products/wrinkle-treatments-and-other-anti-aging-products

- [FDA’s explanation of compounding](https://www.fda.gov/drugs/human-drug-compounding/compounding-and-fda-questions-and-answers) 2025 · FDA’s account of pharmacy preparation and the absence of approval for compounded medicines. https://www.fda.gov/drugs/human-drug-compounding/compounding-and-fda-questions-and-answers

## Reading beyond a headline

The [four-signal overview](/what-fades/) connects the measurements without treating them as treatment targets. The [comparison](/compare/) keeps each substance and research setting distinct. A reported change in cells, animals or a blood measurement needs to remain attached to that setting when it is discussed elsewhere.

A provider’s assessment through Promise Peptides cannot supply missing research evidence.

![Four loose groups of research-paper sheets with their print falling completely out of focus.](/juventa-timber-f62c248e90a9/dust-in-window-light.webp)

![The back of an older adult’s silver-haired head and relaxed shoulders in soft daylight.](/juventa-timber-f62c248e90a9/og-default.webp)

## A question can be the next step.

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