Epitalon, NAD/NMN and GHK-Cu are stacked because each targets a different ageing lever — pineal/telomere signalling, cellular NAD+ supply, and copper-dependent repair/collagen respectively — so the convention is "cover several mechanisms at once" rather than push one hard. That logic is mechanistic and plausible; it is not backed by any trial of the three run together. The strongest individual evidence sits with NMN; the weakest with Epitalon.
There is no validated marker set for this combination, but a longevity stack is one where baseline bloods are most worth having — metabolic panel, fasting glucose/HbA1c and lipids give NMN something to read against, and a clinician conversation matters before adding injected compounds (Epitalon, GHK-Cu) on top of a supplement. Limited combination safety data is a reason for more caution, not less. General information, not medical advice.