I only skimmed this article but seems to suggest that’s not a major concern with their treatment.
Pieper emphasized that current over-the-counter NAD±precursors have been shown in animal models to raise cellular NAD+ to dangerously high levels that promote cancer. The pharmacological approach in this study, however, uses a pharmacologic agent (P7C3-A20) that enables cells to maintain their proper balance of NAD+ under conditions of otherwise overwhelming stress, without elevating NAD+ to supraphysiologic levels.