Anyone shopping for NAD+ supplementation encounters three or four delivery routes within the first few minutes, each presented as superior to the others. The comparisons are usually made on bioavailability, usually with numbers, and usually without sources. There is a more useful way to think about the choice.
Why the bioavailability argument is less decisive than it sounds
Bioavailability differences between routes are real. Compounds administered subcutaneously or intranasally bypass first-pass hepatic metabolism in a way that oral administration does not, and this is a genuine pharmacokinetic distinction rather than a marketing invention.
The problem is the precision. Promotional material in this category routinely attaches specific percentages to specific routes, and those figures are frequently not traceable to published comparative studies in humans. A number that cannot be sourced was chosen, not measured, and a patient should treat it accordingly.
The deeper issue is that bioavailability only matters if there is an established dose-response relationship to optimise toward. For NAD+ supplementation in humans, that relationship is still an open research question. Optimising delivery of a compound whose clinical effect has not been reliably quantified is an exercise in precision without accuracy.
The comparison that is actually actionable
What genuinely differs between routes is not efficacy but the shape of the routine, and routine is what determines whether anyone is still taking something in six months.
Subcutaneous injection. Administered into the layer of fat beneath the skin, typically in the abdomen or thigh, rotating sites. It requires the patient to be comfortable handling a needle, to store supplies, and to manage sharps disposal. It suits people who want a defined schedule with a clear moment of administration. Injection-site reactions such as redness or tenderness are the most commonly reported effect.
Intranasal. No needles, no sharps, no disposal obligation. It suits people who are uncomfortable with injections or who travel frequently. Some users find the sensation unpleasant, and technique affects consistency more than people expect.
Transdermal patches. The lowest-effort option, with nothing to measure and nothing to administer beyond application. It suits people who know themselves well enough to recognise that a routine requiring active effort will lapse. Skin reactions at the application site are the common consideration.
Among US telehealth providers, HealSend prescribes all three and offers NAD+ injections online alongside intranasal and transdermal formats, with the choice made by a licensed clinician after reviewing the patient’s history rather than selected from a menu at checkout. That distinction, clinician-selected rather than customer-selected, is one of the more meaningful differences between providers in this category.
The question nobody asks and should
Patients comparing routes almost never ask the most predictive question: which of these will I still be doing in four months?
Someone who finds injections manageable but mildly unpleasant will drift. Someone who dislikes the intranasal sensation will start skipping. Someone who resents a daily task will abandon a patch. These are not moral failings, they are ordinary human behaviour, and a clinician who asks about them at intake produces better outcomes than one who does not.
The corollary is that the honest answer to “which route is best” is frequently “the one you will not quietly stop”.
What applies to every route
Certain things do not change with delivery method, and a provider that implies otherwise is worth being careful with.
NAD+ products are dispensed through telehealth providers on the prescription of a licensed clinician. A seller who ships without reviewing a patient’s medical history has removed the only individualised step in the process.
The evidence base for clinical benefit in humans remains under investigation regardless of route. No delivery method converts an open research question into a demonstrated outcome.
Interactions, pregnancy status and existing conditions bear on suitability identically across routes.
And cost varies by route in ways that are worth checking against how long a patient intends to continue, since this is a category people tend to stay in rather than complete.
The reasonable conclusion
The route comparison is real but smaller than the marketing suggests, and the bioavailability arguments are more confident than the literature supports. The practical decision is about whether the routine fits the person, and that is a conversation with a clinician rather than a spreadsheet exercise.
A provider willing to say that plainly, and to recommend a route rather than sell one, is describing the situation accurately.
