What is NAD?
NAD = nicotinamide adenine dinucleotide
It is an important substance our bodies make in small quantities. Some supplements can bypass process-limiting steps we have to more directly encourage NAD to be made. Nicotinamide riboside is one supplement that gets this done and studies have shown taking it can even reverse liver and pancreatic cancer, along with minimizing other liver conditions.
Doses range from 150 to 450 mg, but the study that reversed those cancers was closest to the 450 mg a day.
There is no reason to take the larger amounts amounts unless you were specifically addressing an issue it can impact.