Swallowed and injected do not deliver the same molecule
In mice tracked with isotope labels, both compounds injected reached tissues around the body intact. Swallowed, the liver broke them into plain nicotinamide first.
What the study found
Swallowed, both molecules are taken apart before they get far
In mice tracked with isotope labels, nicotinamide riboside and nicotinamide mononucleotide given by injection reached tissues intact. Swallowed, the same two molecules were broken down in the liver into plain nicotinamide first. The pill and the drip are not delivering the same thing.
The caveat · A side result, not the study's aim
This was one result among many in a study built to map how fast NAD is made and consumed across tissues, not a comparison it was powered to make. It tracks where the molecule goes, not whether anything follows from its arriving. No equivalent measurement has been made in people.