For what it's worth, I used 5.6mL and had a poor reaction.
I did some followup testing on it a few days ago and i wonder if it might need some buffering as it's relatively acidic upon reconstitution. Based on reading it appears NAD+ breaks down relatively quickly in acidic
or alkaline environments so i'm not sure how long it will be worthwhile after reconstitution.
I can't say with any certainty that the acidity caused the reaction I had or not...but here's what the pH paper showed (Pure bacteriostatic water top, Reconstituted NAD+ bottom, it seemed to be somewhere between the 3 and 4 when comparing it in person).
View attachment 263634