# NAD+ Research: Human Precursor Trials, the IV Route, and What They Measured > The NAD+ research record, filed by route: the human NMN and NR trials that raised blood NAD+, the mechanism, the rapidly cleared IV route, and the gaps the 2025 review still flags. Cited to source. Mechanism first, then the human precursor trials that moved blood NAD+, then the weakly evidenced injectable route — each finding carried back to its study. ## Before the details This page reads the NAD+ research record. NAD+ (the cell's main energy-handling helper molecule) falls with age, and researchers test whether feeding the body its precursors (the building blocks NMN and NR) pushes it back up. In people, those precursors reliably raise the NAD+ measured in blood. Whether that translates into feeling or aging better is the open question — a 2025 review found the blood numbers consistent but the real-world benefits still mixed. Injected and IV NAD+ has the thinnest evidence of all and is cleared from the blood within hours. Everything below is cited. ## Mechanism: why NAD+ matters and why it falls with age NAD+ does two jobs at once. As a redox carrier (redox is the chemistry that shuttles electrons to release energy), it cycles between NAD+ and NADH to move electrons through glycolysis, the citric-acid cycle, and the mitochondrial electron-transport chain, driving ATP synthesis [5]. As a signaling substrate, it is consumed — physically used up — by three enzyme families: the sirtuins (a family of cellular-maintenance enzymes that cannot work without NAD+), the PARPs (DNA-repair enzymes, chiefly PARP1), and CD38, an NAD-consuming ectoenzyme [5]. The age-related fall in tissue NAD+ is not only slower production; it is faster consumption. CD38 activity rises with age and inflammation, and in mice it is the principal driver of the decline: CD38-knockout animals are protected against age-related NAD+ loss, preserving SIRT3 activity and mitochondrial function [2]. That mechanism — a rising NAD+ sink — is the clearest argument for trying to top the pool back up with precursors [5]. ## What the research measured: reported outcomes of NAD+ precursor trials The reported NAD+ benefits in human trials fall into two tiers, and honesty requires keeping them apart. Tier one — raising blood NAD+ — is well established. NR at 100/300/1000 mg/day for eight weeks raised whole-blood NAD+ by 22%, 51%, and 142% [4]; NMN at 300–900 mg/day for 60 days raised blood NAD+ dose-dependently, with 600 mg/day identified as the optimal dose in that multicenter trial [3]; NMN at 250 mg/day for 12 weeks raised whole-blood NAD+ at weeks 4, 8, and 12, returning to baseline by week 16 after cessation [6]. A 2026 head-to-head found NR and NMN comparably roughly doubled circulatory NAD+, while nicotinamide (NAM) did not [15]. Tier two — hard functional benefit — is mixed. A 10-week NMN trial (250 mg/day) in prediabetic, postmenopausal women significantly increased muscle insulin sensitivity, with no change in body composition or HbA1c [1]. A 12-week NMN trial (250 mg/day) in healthy older men improved gait speed (p=0.033) and left-hand grip strength (p=0.019) without changing muscle mass [7]. But a 2023 review of NAD+-boosting trials concluded that while NAD+ metabolites rose consistently across compounds and doses, most functional endpoints — insulin sensitivity, energy expenditure, exercise capacity, body composition — showed no significant improvement across multiple trials [8]. The 2025 Nature Metabolism review reached the same verdict: consistent blood NAD+ elevation, inconsistent translation to clinical endpoints, and sparse tissue NAD+ data [14]. ## Injectable and IV NAD+: an unapproved compounded therapy with quality risks A NAD injection is the weakest-evidenced route in the entire record, and this digest files it under the caution desk. Injectable and IV NAD+ are compounded preparations — not FDA-approved products — sold in wellness settings, and the controlled data behind them are minimal, mostly pilot or retrospective [14]. There is a documented quality risk on top of the evidence gap: a compounded NAD+ injection has been subject to an FDA Class I recall over elevated bacterial endotoxin [8]. A Class I recall is the agency's most serious category. None of the human precursor work transfers to the needle. The trials that raised blood NAD+ used oral NMN and NR, not infusions [3][4]. No randomized trial establishes a clinical benefit for the injectable route, and infusion run too fast can cause flushing, nausea, and chest or abdominal pressure [14]. ## IV NAD+ therapy: what controlled evidence exists Almost none of the rigorous kind. The NAD IV therapy literature is dominated by pilot studies and retrospective case series rather than randomized, controlled trials, so efficacy for any indication is not established [14]. The pharmacokinetics compound the problem: infused NAD+ is rapidly cleared from plasma, with near-complete removal within the first roughly two hours of infusion in a pilot study, meaning the exposure is brief however large the dose. Against that, the oral-precursor route raises blood NAD+ for days to weeks of chronic dosing [4][6]. ## Clearance: why infused NAD+ disappears from plasma quickly The NAD+ half life question separates the routes more sharply than anything else. NAD+ itself is not freely taken up intact by most cells, and infused IV NAD+ is rapidly cleared — a pilot study found near-complete plasma removal within the first roughly two hours of infusion. Oral precursors behave differently: absorbed and converted, they raise whole-blood NAD+ over days to weeks, and that elevation persists through chronic dosing in 8-to-12-week trials before reversing after cessation [4][6]. Brief plasma spike versus a sustained blood-NAD+ rise — that is the route divide. ## Beyond the precursor trials: the wider mechanism literature The NAD+ field reaches past supplementation. Topical nicotinamide (niacinamide) replenishes the cellular NAD+ pool and, applied to skin, reduced progression of skin aging and hyperpigmentation in clinical trials while being well tolerated — a separate cosmeceutical thread from oral dosing [10]. In animal models, the precursor NR given before noise exposure preserved cochlear ribbon synapses and aided hearing recovery in mice [11], and oral nicotinamide protected against glaucoma in aged mice, with 93% of eyes spared at the highest dose tested [13]. NAD+ metabolism also has a darker edge: in BRAF-inhibitor-resistant melanoma, resistant cells upregulated the NAD+ biosynthetic enzyme NAMPT, and a NAMPT inhibitor depleted NAD+ and ATP and improved survival in xenograft-bearing mice [12]. That dual role — NAD+ also fuels proliferating cells — is why caution is advised around NAD+ supplementation in cancer populations [14]. ## Is NAD+ shot worth it? On the evidence, the injectable route is the hardest to justify. Injectable and IV NAD+ have the weakest controlled evidence of all routes; infused NAD+ is cleared from plasma within hours, and no randomized trial establishes a clinical benefit for the shot [14]. The oral precursors carry the human data, not the needle [3][4]. This is an evidence read, not a recommendation. ## Does NAD make you look younger? The anti-aging claims rest largely on rodent data. In humans, blood NAD+ rises reliably with precursors, but its translation to visible aging endpoints is unproven [14][8]. The one separate exception is topical nicotinamide, which has its own cosmeceutical evidence for reducing skin-aging and pigmentation markers — a skin-surface effect, not a systemic NAD+ result [10]. ## Does NAD IV actually work? Controlled evidence for IV NAD+ is minimal. Infused NAD+ is rapidly cleared from plasma, and most available data are pilot or retrospective rather than randomized, so efficacy for any indication is not established [14]. The route's popularity outruns its evidence base, which is the gap this digest flags plainly. ## Does NAD help with weight loss? Trials have not shown precursor supplementation produces weight loss. In the prediabetic-women NMN trial, muscle insulin sensitivity improved but body composition and HbA1c did not change [1], and the 2023 review found body-composition endpoints unmoved across multiple trials [8]. No cited study supports NAD+ precursors as a weight-loss intervention. --- A night-edition broadsheet on the NAD+ record — the coenzyme filed apart from the NMN and NR precursors that rebuild it, the human trials that raised blood NAD+ kept on their own desk from the poorly-absorbed oral pill and the rapidly-cleared IV drip, and the contested NMN status posted as filed; no clinic behind this masthead and nothing here prescribed, compounded, or sold.