The sublingual route of administration for NMN or NR may bypass the liver's first-pass metabolism, potentially leading to higher plasma concentrations without compensatory nicotinamide rise.

“well the SL route I lost about a lot sublingual put under your tongue try and get it taken up by that and let me explain why this is the case because it might not be obvious if you're listening because you might be saying why would putting it under your tongue be okay but swallowing it not and the reason is when a person swallows the medication it goes through from the stomach into the jejunum and the ileum usually in the jejunum which is the first part of the gut after the stomach it gets absorbed and that blood supply goes straight to the liver through this thing called the portal circulation and so most drugs actually have to be designed with that in mind either immune to the livers metabolism or design such that they're Pro drugs and the liver actually turns them into the right drug when you're talking about putting something under your tongue just like someone who for example carries around nitroglycerin if they run the risk of getting chest pain that drug gets directly absorbed into the circulation and doesn't go through the liver”