NAD+ (nicotinamide adenine dinucleotide) can be taken as an oral supplement, a sublingual tablet, or through IV infusion, but here’s the catch: your body breaks down direct NAD+ before most of it reaches your cells. That’s why the most common approach is taking a precursor, a smaller molecule your body converts into NAD+ after absorption. The two most popular precursors are NMN (nicotinamide mononucleotide) and NR (nicotinamide riboside), both widely available as oral supplements.
Why Precursors Work Better Than Direct NAD+
When you swallow NAD+ directly, enzymes in your small intestine break it apart almost immediately. It gets split into smaller molecules, primarily NMN, before your gut can absorb it intact. Even when NAD+ is delivered intravenously, bypassing digestion entirely, the body metabolizes it rapidly. Within two hours of starting an IV drip, breakdown products already appear in plasma and urine.
NR has a distinct advantage at the cellular level: it can cross cell membranes directly using built-in transport channels called nucleoside transporters. NMN, despite being one step closer to NAD+ in the conversion chain, actually needs to be converted back into NR outside the cell before it can get inside. Once absorbed, both precursors are used by the liver to synthesize NAD+ within minutes. There’s also plain nicotinamide (vitamin B3), a simpler and cheaper precursor. A single 500 mg dose of nicotinamide raised blood NAD+ levels significantly within 12 hours in healthy adults.
Oral Supplements: Forms and Doses
NMN and NR are the two precursors you’ll find most often on supplement shelves, and both come in capsule or powder form. For NMN, a large placebo-controlled trial in 80 middle-aged adults tested daily doses of 300, 600, and 900 mg over 60 days. All three doses raised blood NAD+ levels and were well tolerated, but 600 mg per day hit the sweet spot for both NAD+ concentration and physical performance improvements. Going up to 900 mg didn’t produce additional benefits in that trial.
NR supplements are typically sold in doses of 250 to 300 mg per capsule, with most people taking one or two capsules daily. Clinical data on NR is extensive but uses varying doses, so there’s less consensus on a single optimal amount compared to NMN.
NMN’s regulatory status in the U.S. has been a moving target. The FDA initially ruled in 2022 that NMN couldn’t be sold as a dietary supplement because it was being investigated as a drug. That decision was reversed in September 2025 after a lawsuit by the Natural Products Association, so NMN is now confirmed as a legal dietary supplement in the United States.
When to Take It
Morning is the better choice. A 2023 study published in Nature Communications found that the timing of NAD+ supplementation matters significantly, at least in mice. Raising NAD+ levels right before the active phase of the day improved body weight, glucose tolerance, insulin sensitivity, and liver inflammation in obese mice. Raising NAD+ right before the rest phase did the opposite: it disrupted the liver’s internal clock, misaligned molecular rhythms, and produced weaker metabolic benefits.
The researchers proposed that NAD+ therapies should follow a chronobiology-based approach, meaning you time your dose to align with when your body naturally ramps up activity. For humans, that translates to taking your supplement in the morning, ideally before or with breakfast. Taking it in the evening could interfere with your circadian clock and blunt the metabolic benefits you’re after.
IV NAD+ Infusions
IV therapy delivers NAD+ directly into the bloodstream, skipping digestion. Even though your body still breaks down the NAD+ quickly, the sheer concentration delivered intravenously raises levels of NAD+ and its metabolites far beyond what oral supplements achieve in a single session.
A typical protocol starts with a loading phase. During the first two weeks, you’d receive 100 to 200 mg per session, once a week, to gauge how your body responds. Doses gradually increase over the following weeks, reaching 500 mg by around week four. By weeks seven and eight, some clinics push to 1,000 mg per session. Each infusion takes anywhere from one to five hours depending on the dose, with higher doses requiring slower drip rates to minimize discomfort.
After six to eight weeks of loading, most people shift to maintenance: one session every two to four weeks at 500 to 1,000 mg. IV therapy is significantly more expensive and time-consuming than oral supplements, so it tends to appeal to people seeking aggressive intervention for energy, cognition, or recovery rather than general wellness.
Adding TMG as a Companion Supplement
You’ll often see trimethylglycine (TMG, also called betaine) recommended alongside NAD+ precursors. The reasoning is straightforward: when your body makes NAD+ from precursors like NMN or NR, one of the byproducts is nicotinamide, which gets recycled through a process that consumes methyl groups. Methylation is essential for DNA maintenance and dozens of other cellular processes, so the concern is that high-dose NAD+ precursors could drain your methyl donor pool over time.
TMG is a potent methyl donor. Taking it alongside your NAD+ precursor is meant to replenish what the NAD+ synthesis pathway uses up. Most TMG supplements provide 750 to 3,000 mg per serving, and studies in humans have used anywhere from 500 to 9,000 mg daily, usually split into two or three doses. A common pairing is 500 to 1,000 mg of TMG for every 500 to 600 mg of NMN or NR.
Side Effects to Watch For
Oral NMN at doses up to 900 mg daily was safe and well tolerated in clinical trials lasting 60 days. The most commonly reported issues with NAD+ precursors at higher doses are mild: stomach discomfort, nausea, and occasional headaches. These tend to resolve within the first week or after reducing the dose.
Direct NAD+ at high doses, particularly through IV, carries a different side effect profile. Reported reactions include insomnia, fatigue, and anxiety. During IV infusions specifically, chest tightness, nausea, and cramping can occur if the drip rate is too fast, which is why clinics start low and infuse slowly. These symptoms typically ease when the infusion rate is reduced.
How Quickly Levels Rise
NAD+ levels in the blood respond faster than most people expect. With a single 500 mg oral dose of nicotinamide, a measurable and significant increase appeared within 12 hours. The elevation showed signs of persisting at 48 hours, though the effect was starting to taper. With daily NMN supplementation at 600 mg, the clinical trial measured meaningful changes in blood NAD+ concentration over its 60-day study period, with physical performance improvements emerging on a similar timeline.
IV infusions produce the fastest spike, with NAD+ metabolites detectable in the blood within two hours of starting the drip. But that rapid rise also means rapid clearance, which is why IV protocols emphasize repeated sessions rather than one-off treatments. For oral supplementation, consistency matters more than any single dose. Taking your precursor daily, in the morning, at a dose in the 300 to 600 mg range for NMN, is the approach best supported by current human data.