This has links to the free study that found a metabolite from NAD creation has some bad effects:
https://pubmed.ncbi.nlm.nih.gov/34580423/
Strangely, early nicotinamide riboside studies pointed to the creation of a large amount of 4-pyridone-3-carboxamide-1-β-D-ribonucleoside (4PYR) as a good indication that the supplementation was making what the body needed. Of course, there are multiple metabolites the body makes, but this bad one appears to come from an excess situation, from other items I read. It would seem better to time-release it, not have a big dose all at once.
Thanks