There appears to be some danger in using NAD+ without the supervision of an experienced physician.
"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 chemical the parent comment linked is different.
NAD itself isn’t usually supplemented because it’s broken down by your digestive system. So NAD precursor supplements have been available for a while: NR and NMN specifically. These are the precursors they were talking about.
The actual drug used in this study has a different mechanism of action. It’s not directly available as a supplement, but like the parent commenter discovered you could technically find a chemical supply house to synthesize a tiny quantity of it.
Most people with Alzheimer’s are older and would probably trade having their cognitive abilities back even with increased risk of cancer