Intravenous NAD+ administration likely increases intracellular NAD+ levels indirectly through breakdown into NR and NMN, though it may not be the most efficient method.

“so i think you end up with you know probably effective nad supplementation when you go the iv route in other words taking iv nad will probably increase into intracellular nad levels though not directly because there's not a transporter but it goes through this sort of circuitous route to get there so it might not be the most efficient way to do it”

“in other words when you give intravenous nad there is no transporter to take nad into a cell but that nad breaks down into things like nr and nmn and in the vascular system we know that those things can get taken up at least into some cells”

“Oral vs. IV nicotinamide riboside”