# NAD+ and the Brain in the Research Literature: Cognition, Neurodegeneration, IV > NAD+ and the brain in the research literature: the Alzheimer's-model NR study, Parkinson's reviews, the 750 mg IV cognition pilot, and the long-COVID NR RCT. Cited, route by route. A neuro watchlist: the Alzheimer's-model and Parkinson's evidence, the IV cognition pilot, and the long-COVID trial — each tagged by how strong its controlled data really is. ## The short read This page covers NAD+ and the brain — what the cognition and neurodegeneration studies measured, read as a watchlist where each finding is rated by evidence strength. Brain NAD+ falls with age, and the precursors NMN and NR are studied to see whether raising it helps neurons [8]. The strongest brain data so far are from animal models; the human data are early. The IV route, the one most marketed for the brain, has the weakest controlled evidence of all [7]. Each finding below is tagged by species and route so a mouse study is never read as a human result. ## Why the brain is an NAD+ target Decreased NAD+ in the brain is a hallmark of aging and is closely associated with neurodegeneration [8]. The salvage enzyme NAMPT is highly expressed in the hippocampus and linked to neural stem and progenitor cell NAD+ biosynthesis, which is part of why NAMPT is studied as a candidate target in neurodegenerative-disease biology [11]. Reviews of NAD+ in Parkinson's disease describe three proposed neuroprotective mechanisms of NAD+ repletion: restoring mitochondrial function in dopaminergic neurons, promoting proteostasis (protein quality control), and immune modulation [8]. This is the mechanistic case; the outcome data below are where it is tested. ## The energy-metabolism thread behind the brain case The brain rationale rests on the same energy biology that shows up in other high-demand tissues. NAD+ is the redox carrier that drives ATP production, and where NAD+ biosynthesis falters, mitochondrial capacity falls with it. In mouse myoblasts and intact skeletal muscle, knocking down the salvage enzyme NAMPT lowered NAD+ and impaired maximal respiratory and oxidative-phosphorylation capacity, while the precursor NR restored NAD+ and raised respiratory capacity [10]. In human muscle, sarcopenia in 119 older men tracked with low NAD+ and reduced mitochondrial oxidative capacity through perturbed biosynthesis and salvage [9]. Neurons are likewise energy-hungry and salvage-dependent, which is why a falling NAD+ pool — and the high hippocampal expression of NAMPT [11] — frames the brain as a plausible NAD+ target. It is mechanism, not proof of cognitive benefit. ## The Alzheimer's-model evidence (preclinical) The clearest mechanistic brain result is preclinical. In APP/PS1 transgenic Alzheimer's-disease mice, NR supplementation for 5 months raised brain NAD+, reduced proinflammatory cytokine expression, decreased microglial and astrocyte activation, lowered NLRP3 inflammasome expression, and improved cognitive and synaptic function — with the effect working through normalization of the cGAS-STING innate-immune pathway [6]. The study also reduced DNA damage, apoptosis, and cellular senescence, and noted that human Alzheimer's fibroblasts showed a similar NAD+-depletion pattern [6]. This is a mouse-model finding: strong on mechanism, not a demonstration of benefit in people. ## Parkinson's disease: early human signals Parkinson's disease research has moved further toward humans, but remains preliminary. Beyond the mechanistic case, preliminary NR trials in Parkinson's-disease patients have shown increased cerebral and whole-blood NAD+ with an association to clinical improvement, while the reviews stress that dedicated clinical trials are still required [8]. The pattern — NAD+ goes up, with a hint of clinical change but no definitive efficacy — recurs across the neuro literature. ## Long-COVID: the first dedicated NR RCT The newest human brain data come from long-COVID. A 24-week double-blind randomized controlled trial in 58 long-COVID patients found that NR significantly elevated NAD+ but did not show a significant group-level difference in cognitive scores versus placebo; within-group improvements in fatigue, sleep quality, depression, and executive function were observed in NR-treated participants [14]. It is the first RCT of NR specifically in a long-COVID population — a meaningful step that nonetheless missed its between-group cognitive endpoint. ## NAD+ injections and IV infusions in the literature The route most marketed for the brain has the least controlled support. The most-cited human cognition data is a pilot: five consecutive daily IV infusions of 750 mg/day improved performance on 6 of 8 neuropsychological tests, versus 2 of 8 for saline [7]. It is a pilot, not a randomized efficacy trial. Infused NAD+ is also cleared from plasma within roughly two hours [7], so any central effect would have to arise from a brief systemic exposure. Compounded injectable NAD+ further carries documented quality risk — the FDA issued a Class I recall of a compounded NAD+ injection for elevated bacterial endotoxin — and such products are unapproved. ## IV NAD+ therapy: what controlled data exist Almost none. The controlled evidence for IV NAD+ therapy is limited to small pilot and retrospective work; the 750 mg/day, 5-day cognition pilot and the 6-hour pharmacokinetic study [7] are the most-cited human examples, and no large randomized trial has established efficacy. The honest read is that IV NAD+ is an unapproved compounded wellness therapy with rapid plasma clearance and documented contamination risk, studied far less rigorously than the oral precursors covered on [NMN vs NR precursors](/nmn-vs-nr). ## What is an NAD injection? An NAD injection or IV infusion delivers NAD+ directly into the bloodstream, used in wellness and clinical settings. Controlled evidence is limited, infused NAD+ is rapidly cleared from plasma within about two hours [7], and compounded injectables are unapproved and carry contamination risk — the FDA issued a Class I recall of one for endotoxin. ## Is an NAD+ shot worth it? The controlled evidence for IV/injectable NAD+ is the weakest in the field. A 5-day, 750 mg/day IV pilot improved 6 of 8 cognitive tests, but rigorous trials are lacking and plasma NAD+ clears within hours [7]. This summarizes the research, not a value judgment for any individual. ## When should you inject NAD+? Published IV protocols are research and clinic infusion schedules — for example, 750 mg/day over several hours for 5 consecutive days [7] — not consumer timing guidance. No human dosing or timing instructions are given here; the figures describe what specific studies administered. ## Does NAD IV actually work? IV NAD+ has the weakest controlled evidence of any route. Pilot data suggest cognitive changes — 6 of 8 tests improved over 5 days at 750 mg/day — but plasma NAD+ is cleared rapidly [7] and large randomized trials are absent, so efficacy is unproven. --- The NAD+ literature read like an order book — the coenzyme and its precursors NMN and NR each listed apart, the blood-NAD+ the trials actually moved quoted to source, and the rapidly-cleared IV route flagged as the weak-data listing; no clinic behind this desk and nothing here ordered, infused, dispensed, or sold.