NAD+ is not a stimulant. It is the substrate your mitochondria use to convert food into ATP and the substrate sirtuins and PARPs use to maintain the genome. Every cell in your body runs on it.
Levels fall steadily with age — by roughly half between twenty and fifty. The downstream consequences are predictable: less energy, slower DNA repair, dampened sirtuin signaling, drifting circadian rhythm. Most modern longevity protocols start here because everything else assumes there is enough NAD+ to do the work.
Sub-Q delivery sidesteps the absorption problem with oral precursors. The molecule arrives intact, refills the intracellular pool, and the rest of the longevity stack has a substrate to work against.