NAD+ for Long-COVID Brain Fog: What's the Evidence?

If you're dealing with the cognitive fog that can linger after COVID-19, you've probably seen NAD+ — as a supplement, an IV drip, or a nasal spray — pitched as a fix. The pitch has real mechanistic appeal, and unlike most NAD+/brain-fog claims, this one has finally been put to a direct randomized test. The honest summary up front: **NAD+ replenishment is a biologically reasonable idea for long COVID, but the first randomized controlled trial that tested it raised NAD+ levels and did not significantly improve cognition, fatigue, sleep, or mood.** That is the most important sentence on this page, and it's worth understanding why the idea was plausible — and why a plausible idea still needs a trial.

First, what "long-COVID brain fog" actually is

"Long COVID" — formally **post-COVID-19 condition** — is generally defined as symptoms that persist roughly three months after a SARS-CoV-2 infection, last at least two months, and aren't explained by another diagnosis¹. Cognitive dysfunction — the slowed thinking, word-finding trouble, and poor concentration people call "brain fog" — is one of its hallmark features alongside fatigue¹.

It is not a vague or imagined symptom. A large community study published in the *New England Journal of Medicine* measured cognitive deficits after COVID-19 that scaled with severity — on the order of a few IQ points in those who recovered quickly, larger in people with persistent long-COVID symptoms². So the target is real and measurable. The open question is whether raising NAD+ does anything about it.

Why NAD+ became a candidate

NAD+ is a coenzyme at the center of how cells turn fuel into energy. The reason researchers took it seriously for long COVID specifically — rather than as one more generic "energy" supplement — is that long-COVID biology points toward a cellular **energy-production problem**.

Multiple lines of evidence describe **mitochondrial dysfunction** in post-acute SARS-CoV-2 infection, and reviews have proposed that **disruption of the NAD+ metabolome** is part of that picture, plausibly contributing to the persistent fatigue and metabolic abnormalities seen in patients³. Separately, the cognitive component of brain fog has been framed as a **neuroinflammation** phenomenon — microglial activation and inflammatory cytokines disrupting normal cognition⁴. NAD+ sits upstream of both energy metabolism and several stress-response pathways, so "top up NAD+, support struggling cells" is a coherent hypothesis.

A coherent hypothesis is exactly that, though — a reason to run a trial, not a result. NAD+ products routinely cite this kind of mechanism *as if it were proof*. It isn't. So what happened when someone actually tested it?

The trial that tested it directly

In 2025, *EClinicalMedicine* published the first randomized, placebo-controlled trial of an NAD+ precursor for long COVID. Researchers gave **nicotinamide riboside (NR) at 2,000 mg/day** to community-dwelling adults with long COVID, over roughly 20 weeks, with a placebo-controlled comparison⁵.

The supplement did what NAD+ precursors reliably do: NR **raised blood NAD+ levels 2.6- to 3.1-fold**. The pharmacology worked. But on the outcomes people actually care about, there were **no significant differences versus placebo** — not in cognition (across multiple cognitive measures), not in fatigue, not in sleep quality, and not in anxiety or depression symptoms⁵. The number in the blood moved; the symptoms did not.

This is the single most relevant data point for anyone considering NAD+ for long-COVID fog, because it tests the *exact* claim — an NAD+ precursor, in *long-COVID patients*, measuring *cognition and fatigue* — rather than extrapolating from aging or other conditions.

### What the "early promise" headlines were actually about

You may have seen coverage describing the same trial as showing "early promise." That framing comes from the study's **exploratory, within-group** analyses, which hinted at improvements in executive function, fatigue, sleep, and mood after about 10 weeks of NR⁵. It's worth being precise about what that means.

A within-group, exploratory signal is *hypothesis-generating*, not confirmatory. People in trials — including those on placebo — often improve over months for reasons unrelated to the pill: natural recovery, regression to the mean, and the placebo effect itself. The whole point of the **placebo-controlled, between-group** comparison is to subtract those out, and once you do, the NR-versus-placebo difference wasn't significant⁵. So the honest read is: the controlled comparison was null, the exploratory hints justify a *larger* trial, and neither one is evidence that NAD+ reliably lifts long-COVID brain fog today.

This fits the broader NAD+/cognition pattern

The long-COVID result isn't an outlier — it matches what NAD+ research keeps showing across conditions. Precursors raise the biomarker reliably (an oral NMN formulation increased circulating NAD+ and its metabolome in older adults⁶), but the cognitive payoff keeps failing to appear. The cleanest example outside long COVID: a randomized trial of NR in older adults with mild cognitive impairment **raised NAD+ but did not improve cognition** versus placebo⁷.

The one frequently-cited "positive" cognition trial — in Alzheimer's patients — used a **multi-ingredient cocktail** (NR combined with L-serine, N-acetylcysteine, and L-carnitine tartrate), so any benefit can't be pinned on NAD+/NR alone and doesn't transfer to long-COVID fog⁸. Across the board, raising NAD+ is the easy part to prove; changing how a person thinks and feels is the part that keeps not happening. For the full version of this pattern, see our pillar guide, Does NAD+ Help Brain Fog?, and the deeper review, NAD+, Brain Fog & Focus: What the Evidence Shows.

What about IV or nasal NAD+ for long COVID?

Long-COVID clinics often market **IV NAD+** drips, and you'll find **nasal NAD+** sprays sold "for the brain." For long COVID specifically, the efficacy evidence here is even thinner than for oral precursors — essentially nonexistent. The only human parenteral-NAD+ data is a small pilot that simply tracked how NAD+ and its metabolites moved through plasma and urine during a 6-hour IV infusion, with **no cognitive or fatigue outcomes measured at all**⁹. Nasal NAD+ for cognition is unstudied in any rigorous trial. So a drip or spray sold "for long-COVID brain fog" is making a claim no trial has tested — we unpack the route question in Nasal NAD+ for Focus: Is There Evidence?.

On safety, the more reassuring data is again for *oral* precursors: a randomized high-dose NR trial found it generally safe and well tolerated¹⁰. But "well tolerated" is not "it worked," and oral-NR safety says nothing about injectable or nasal NAD+.

So should you try NAD+ for long-COVID brain fog?

Here's the honest framing. NAD+ for long COVID is **mechanistically plausible and not proven** — and unusually, we now have a direct trial showing the biomarker can move without the symptoms following⁵. That doesn't make NAD+ useless forever; larger trials may yet find a subgroup or a regimen that helps. It does mean that, *today*, no one can promise you a cognitive or fatigue benefit, and you should be skeptical of any product that does.

More importantly, long COVID is a medical condition, not a supplement gap. The highest-value moves are clinical:

- **Work with a clinician** — ideally a long-COVID or post-COVID program — to assess and manage your specific symptom pattern. - **Rule in the treatable contributors** that also drive ordinary brain fog and frequently coexist with long COVID: poor or insufficient sleep, thyroid dysfunction, iron deficiency or anemia, and depression or anxiety. Each is testable and treatable, and addressing them does far more than any NAD+ product. We walk through the full list in What Actually Causes Brain Fog?. - **Respect post-exertional symptoms.** Many people with long COVID worsen after pushing through fatigue; pacing is a recognized part of management, not a sign of weakness.

If, after all that, you still want to try an NAD+ precursor, treat it as a low-confidence experiment layered on top of real care — not the centerpiece — and judge it by how you feel, not by a NAD+ blood number that's almost guaranteed to rise regardless. For an evidence-tiered look at the broader brain-fog supplement shelf, see the best supplements for brain fog, rated by evidence. And if you're weighing cognitive-energy products against this evidence bar rather than the marketing, our best cognitive-energy picks rank providers honestly.