Limited clinical data: While animal studies are promising, more research is needed to confirm the efficacy and safety of oral NAD+ supplementation in humans, particularly regarding optimal dosages and long-term effects.
Brain barrier challenge: Crossing the blood-brain barrier to reach the brain is a significant obstacle for orally administered NAD+ precursors.

I was taking it for about a year plus. I hadn't taken it for a month or so. I'm not sure if I saw any differences because I take so many other supplements. I may go back to it.