You have been injecting for six weeks. You might feel better. You might have slept well last Tuesday for unrelated reasons. The obvious next thought is to measure something, and the honest answer is that what you can measure is not what you want to know.
What can be measured
NAD⁺ in blood, and in some tests inside the cell. That is a real assay giving a real number, and one seller we cover builds its whole model on it: measure your intracellular NAD⁺, take the product, measure again, adjust the dose. The test runs $198.
That is more rigorous than the category norm, and worth saying plainly before the criticism. Most sellers offer nothing of the kind.
Why it still does not answer the question
Because raising the number was never the part in doubt. The randomized trials of oral precursors established that they raise blood NAD⁺ — that is the one thing this field has repeatedly shown. What those same trials struggled to show is that the rise produces an outcome anyone can feel.
So a before-and-after test tells you the product did the thing already known to happen. It cannot tell you whether it helped, because the gap between the biomarker and the benefit is exactly where the evidence thins out. Measuring the first more precisely does not narrow that gap.
There is a version of this worth paying for: if a dose was too low to move the marker at all, a test would reveal that. That is a real use. It is a narrower one than the marketing implies.
What a single reading is worth
There is a second problem, and it is arithmetic rather than philosophy. A community study that measured whole blood NAD⁺ in 1,518 adults found an average of 33.0 µmol/L with a standard deviation of 5.5 [1]. That spread is between people of the same age, on the same day.
So an individual reading arrives inside a wide normal range, and a change smaller than a few µmol/L is hard to distinguish from where you happened to sit in that range to begin with. The same study — the one behind the decline-with-age question — put the difference between men under 30 and men over 60 at 2.16 µmol/L, with a 95% CI of −4.16 to −0.15 [1] — under half a standard deviation for four decades of aging, and an interval whose upper end sits close to no difference at all.
A test can still show a real, large rise after supplementation. It is the small movements that mean less than they look like.
Why your own impression is unreliable here
This is not a comment on anyone’s self-awareness. It is why trials use placebo groups at all.
- You chose this. You spent money, you expect it to work, and expectation reliably changes reported energy and mood.
- You started when you felt worst. People begin treatments at a low point, and low points tend to be followed by better ones regardless.
- You changed other things. Almost nobody starts a longevity protocol and changes nothing else about sleep, alcohol or exercise.
- The outcomes are soft. Energy and focus are the hardest endpoints to assess in yourself, which is why the trials that measured them used walking tests and questionnaires rather than asking people if they felt better.
The test that is worth doing
A different one, for a different reason. One seller will not prescribe until a comprehensive metabolic panel has checked kidney and liver function, and says the blood test is not optional.
That is not measuring whether it works. It is checking the treatment is appropriate for you before you start, which is ordinary medicine and notable mainly because so few sellers in this category require it. If you are choosing between providers, a service that insists on baseline bloodwork is telling you something about how it operates.
So what should you actually do?
Decide in advance what would change your mind, and write it down before you start. A specific, checkable thing — a sleep score, a weekly step count, a timed task — beats a general impression at week eight, because by then the impression has had a month to be shaped by the fact that you are paying for this.
Then treat the money as the main variable. If you cannot tell, the honest conclusion is that you cannot tell — and what you signed up to decides what that costs you. If you are still deciding at all, the oral route has the human evidence behind it and costs a fraction as much.
None of this is advice to stop something a clinician prescribed. It is a way of thinking about a product sold on a feeling, in a category where the feeling is the only endpoint most buyers ever assess.