NAD+ is not a peptide and not a drug. It is a coenzyme present in every cell, essential to converting food into usable energy and to the function of several repair enzymes, and its levels decline with age. That decline is real and it is the basis for an entire supplement category. The important thing to understand is that four different products are sold under this banner and they are not equivalent. Taking NAD+ itself by mouth is largely futile because the molecule is broken down before absorption. The precursors, nicotinamide riboside and nicotinamide mononucleotide, are absorbed and have genuine trials behind them, though the results are more modest than the marketing. Intravenous NAD+, sold by wellness clinics, has the weakest evidence of the four and the highest price.