An important molecule still needs a good trial
NAD+ is a coenzyme, a molecule that helps enzymes work. It helps cells use energy and maintain themselves. It isn't a peptide, despite often appearing in the same online conversation.
A review of NAD+ and ageing biology explains why it interests researchers. But knowing a molecule is essential doesn't show that giving more improves someone's health.
What did the supplement studies test?
NR means nicotinamide riboside. NMN means nicotinamide mononucleotide. Both are precursors: substances the body can use to make NAD+. They're different from giving NAD+ itself.
An oral NR trial found higher blood NAD+ levels. It found no significant difference in adverse events from placebo during the study. That's useful information about that supplement and study period, rather than proof of longer life or lasting safety.
One NMN study in postmenopausal women with prediabetes went beyond a blood NAD+ measurement. It found that muscle responded better to insulin, the hormone that helps control blood sugar. That's a specific result in a specific group. It doesn't establish a general rejuvenation effect.
Where does that leave the bigger claims?
A review of human precursor studies found limited and inconsistent evidence of health benefits. Blood levels can rise while questions about useful changes in health remain open. We also know less about NAD+ levels in different tissues.
These findings don't establish longer human life. Nor can an oral supplement study establish the benefits or safety of intravenous NAD+, given into a vein. The way a substance enters the body changes the question.
Safety needs its own evidence
A short oral study can't establish long-term safety or safety by another route. For US compounded preparations, the FDA explains that these aren't approved drugs. Its warning covers safety, effectiveness and quality before sale.
The comparison helps separate a changed blood measurement from a health benefit. Keeping those apart makes the research easier to read.