I've been taking Alive by Nature's NMN powder sublingually with dilute DMSO to improve its penetration of the subl/bucal membranes and into the blood stream.
NMN weighs 343.22 Daltons so should absorb and be transported in the blood stream via sublingual/bucal administration. I add about a third dropper of DMSO/ionic water (~30% DMSO) to promote penetration. (I have a cocktail of ingredients that I take this way first thing in the morning.)
This tastes bad enough, but not too bad for a long-time LongeCity member.
I also occasionally administer NAD+ nasal spray.
I also occasionally take NR/pterostilbene. But I've been taking high-dose niacin and/or niacinamide for dozens of years with the addition of D-ribose this last year. (There is an age-related decrease in D-ribose production on the body, so supplementing D-ribose makes sense.)
So I wonder that one of the reasons I'm told by multiple individuals (voluntarily) that I look 20 years younger than my siblings is that I am and have long been replete in NAD+.
There are multiple methods to maintain NAD+, not just with NR.