NAD+ can make your mitochondria work better if you have trouble making or recycling it. If you have enough already (and that's not your problem, its unlikely it will help.
Nicotinamide riboside is not the same thing. It's a couple of conversions short of NAD+. If your pathway isn't working, it won't convert to NAD+. I've tried it multiple times, at high doses, and it hasn't done anything at all for me, ergo, my pathway doesn't work.
NADH is closer. It recycles back to NAD+. I've found 10-20mg of the Enada NADH product to help for a couple of hours, enough to get through a workout in the gym (though I still had POTS slow me down).
I learned I'm getting 150mg of NAD+ in my IVs, which does the most for me. I feel almost normal for 36-48 hours and can exercise. I've been taking 25-50mg a day of the sublingual product, before exercise, and my life has been more normal.
It helps my mitochondria make more ATP, but it is not solving my antibodies, any infections I may still have, any nutrient deficiencies, or my MCAS problem.
And, I seem to have a peroxynitrite problem due to low BH4 recycling which leads to ssuperoxide production as my mitochondria make ATP. So, increasing ATP production can increase superoxide production and damage mitochondrialndrial membranes if enough superoxide dismutase cannot be produced (which may be the case with homozulygous SOD SNPs).
Enhancing BH4 production and recycling, reducing peroxynitrite production, increasing SOD production, and providing nutrients to replenish membranes might be helpful co-strategies. Some may need additional CoQ10, carnitine, etc. as well.
So, it may be wise for at least some of us to move cautiously with this one unless we have the supports in place.
Dumping a huge amount of NAD+ into someone with ME/CFS seems, at best, a short term solution, unless one has fixed every other possible problem and only needs ATP alone. Certainly, NAD+ can help processes that use it to work better, but I doubt its a cure and it seems cavalier of someone to market it as a CFS cure.
I trust my doctor, who is quite familiar with it (as well as with the use of AMP in IVs) and he felt the 150mg of NAD+ as a part of a balanced nutrient and mitochondrial support program was appropriate for me as we work on the other pieces.