It is unclear if oral NAD precursors like NMN, NR, niacin, and nicotinamide can achieve effective doses in humans due to breakdown to niacin in the gut.

“what's entirely unclear is what raising blood NAD translates to in terms of getting more NAD into cells I don't know that that's specifically cells like skeletal muscles right I think based on Josh Rabinowitz his work I also had Josh Rabinowitz on the podcast to talk about this um and I trust Josh on this um much more than I would trust any marketing material um because he doesn't have a dog in this fight right right he just you know he just does the work and um what Josh's research soed which is basically NAD flux research has demonstrated that look the liver is probably the place of greatest uptake uh in addition to blood and that's about all we know like it's not clear how much of this is getting into other cells”