Search "NAD+ side effects" and the list comes back fast: nausea, cramping, chest tightness, a racing heart, a hot flush across the face. Most of the pages behind that list are run by IV clinics, and most of those reactions come from a drip running into a vein.
That matters if what you're actually considering is a capsule. An NAD+ infusion and an NAD+ supplement share a name, but they don't reach your cells the same way, at the same speed, or in the same form. The side effect profile follows the route.
Here's the part almost no one mentions: no clinical trial of oral NAD+ capsules has been published yet. The first one registered is not yet recruiting. So everything anyone tells you about capsule side effects is an inference, and it's worth knowing what the inference rests on.
- The scary list mostly comes from IV infusions. In a 2026 review of clinic records, all six people given IV NAD+ at a client-controlled pace reported moderate to severe cramping, nausea, and chest pressure during the drip (Reyna et al., Frontiers in Aging, 2026).
- Capsule trials look very different. Across 10 randomized trials of the precursor NMN with 383 adults, adverse events were no more common than on placebo, and liver enzymes didn't move (Yang et al., Nutrients, 2026).
- Oral NAD+ itself has no published trial yet. Swallowed NAD+ is mostly broken down in the small intestine into smaller precursor molecules, which is why precursor trials are the closest evidence available.
- The group that most needs a doctor's input is people in active cancer treatment. A 2026 Case Western study found NAD+ precursors helped pancreatic cancer cells resist chemotherapy in lab and mouse models.
- Timing has one trial behind it, and it's small. Older adults who took NMN in the afternoon showed the largest improvements in leg function and drowsiness.
Three Different Things Get Called "NAD+"
NAD+ (nicotinamide adenine dinucleotide) is a coenzyme every cell uses to turn food into energy and to run repair enzymes. When people say they're "taking NAD+," they usually mean one of three things:
- An NAD+ capsule. The whole molecule, swallowed. It's large, and most of it doesn't survive digestion intact. A 2023 review in Current Nutrition Reports summarizes the animal work plainly: "ingested NAD+ was mainly hydrolyzed in the small intestine by pyrophosphatases present in brush border cells or intestinal secretions" (Alegre & Pastore, 2023). What gets absorbed is largely smaller pieces: NMN, NR and nicotinamide.
- A precursor capsule. NMN (nicotinamide mononucleotide), NR (nicotinamide riboside) or nicotinamide, which your cells assemble into NAD+. This is where nearly all the human trial data lives.
- An IV drip or injection. NAD+ delivered straight into the bloodstream, usually at a clinic, often at hundreds of milligrams per session.
Because a capsule of NAD+ is largely converted to precursors before it's absorbed, the precursor trials are the most relevant safety evidence for it. IV data tells you almost nothing about a capsule, because the IV route skips digestion entirely and delivers the dose far faster.
Worth knowing: the first registered trial of an oral NAD+ capsule (NCT07692633, 80 adults, two capsules daily after breakfast for 56 days) lists an estimated start of August 2026 and is not yet recruiting. Its results are expected no earlier than 2027.
What the Capsule Trials Actually Recorded
The most useful single source here is a 2026 systematic review and meta-analysis of oral NMN in adults. It pooled safety data from 10 randomized controlled trials covering 383 participants, at doses from 250 to 2,000 mg a day for between 14 days and 24 weeks (Yang et al., Nutrients, 2026).
- Any adverse event: 58 of 230 people on NMN versus 38 of 153 on control. The risk difference was essentially zero (−0.008).
- Serious adverse events and dropouts due to side effects: no difference between groups.
- By body system: no significant increase in digestive, nervous system, or skin and allergic reactions.
- Liver: no meaningful change in ALT or AST, the two standard liver enzymes.
Two individual trials fill in the picture at higher doses:
- NR at up to 1,000 mg a day for 8 weeks. In overweight but otherwise healthy adults, NR raised whole-blood NAD+ by 22%, 51% and 142% at 100, 300 and 1,000 mg, within two weeks. There were "no reports of flushing and no significant differences in adverse events" between NR and placebo, and LDL cholesterol didn't rise (Conze et al., Scientific Reports, 2019). The study was funded by ChromaDex, which sells NR.
- NMN at 1,250 mg a day for 4 weeks. In 31 healthy adults aged 20 to 65, blood work, urine, and body composition stayed within normal physiological variation, and there were no severe adverse events (Fukamizu et al., Scientific Reports, 2022). It was funded by an NMN manufacturer.
When side effects do show up across the precursor literature, they're the minor kind. A 2022 review lists them as "diarrhea, nausea, rashes, flushing, calf cramps," among others, and notes that most side effects reported with nicotinamide, NR and NMN are minor (Poljšak et al., 2022).
Why IV NAD+ Is a Different Experience
The IV literature is thinner, and it points in two directions depending on how fast the drip runs.
In a controlled pilot study, researchers infused 750 mg of NAD+ into healthy men over six hours, about 2 mg per minute, and reported that "no adverse events were observed during the 6 h infusion" (Grant et al., Frontiers in Aging Neuroscience, 2019). Eight men received NAD+ and three got saline, so it's a small study.
Commercial wellness clinics rarely run a drip for six hours. A 2026 retrospective review of records from one clinic chain looked at 500 mg IV NAD+ given on four consecutive days, with the pace set by each client's tolerance. The infusions averaged about 97 minutes. The authors reported that "all clients (n = 6) in the NAD+ group reported moderate to severe abdominal cramping, diarrhea, nausea, vomiting, increased heart rates, pain in throat, congestion, and chest pressure during infusion." Clients given IV NR instead finished faster, in about 37 minutes, with only minor tingling and cramping (Reyna et al., Frontiers in Aging, 2026). The authors still concluded both compounds "appeared safe," with no clinically significant changes in liver enzymes.
| NAD+ capsule | IV NAD+ drip | |
|---|---|---|
| What reaches the blood | Mostly smaller precursors, after digestion | Intact NAD+, directly |
| Speed | Gradual, over hours | Set by the drip rate |
| Human safety data | Indirect: precursor trials up to 24 weeks | A few small studies and clinic records |
| Reactions reported | Occasional mild stomach upset, headache | Cramping, nausea, chest pressure, faster heart rate, mostly during the infusion |
| What usually helps | Taking it with food | Slowing or stopping the drip |
The Flushing Question
"Will NAD+ make me flush?" is one of the most common questions, and the answer depends on which molecule you mean.
The classic niacin flush, a hot, red, prickly wave across the face and chest, is caused by nicotinic acid, one specific form of vitamin B3. It triggers a receptor in the skin that sets off a prostaglandin release and widens the blood vessels. NMN, NR, nicotinamide and NAD+ are all related to vitamin B3, but they don't act on that receptor the same way, which is why the 1,000 mg NR trial recorded zero cases of flushing.
The warmth people describe during an IV NAD+ session is a different phenomenon. It's tied to the infusion itself and usually fades when the drip slows. If you're taking a capsule and you do flush, check the label for nicotinic acid, often listed simply as "niacin." Soleu's formula contains none.
Why You Might Feel Off After Taking NAD+
If you've started an NAD+ or precursor supplement and something feels off, these are the usual suspects, roughly in order of likelihood:
- An empty stomach. Nausea and loose stools are the most common complaints across the precursor literature. Taking the dose with a meal is the simplest fix, and it's what the first oral NAD+ trial instructs participants to do.
- Stacking B3 sources without realizing it. Multivitamins, energy drinks, and "longevity" blends often contain niacin or nicotinamide. Adding an NAD+ product on top raises the total more than you might expect.
- A mild headache in the first days. Headache appears in the minor side effect lists for these compounds. It's usually short-lived. If it persists, stop and reassess.
- Sleep that feels different. Some users report feeling more alert when they take NAD+ products late in the day. That's anecdotal; no trial has measured it as a side effect. The one timing trial, covered below, actually found afternoon intake reduced drowsiness.
- An IV that ran too fast. If the "weird" feeling happened during or right after an infusion, the rate is the first thing to ask about.
Anything beyond mild and short-lived, such as rash, persistent stomach pain, chest pain, or palpitations after a capsule, is a reason to stop and talk to a doctor, not to push through.
Who Should Skip NAD+ or Ask a Doctor First
People in active cancer treatment. This is the most important caution, and it's often described inaccurately. In April 2026, researchers at Case Western Reserve University published a study in Cancer Letters testing three NAD+ precursors, NMN, NR and nicotinamide, on pancreatic cancer. In cell and mouse models, the precursors helped cancer cells resist three standard chemotherapy drugs (oxaliplatin, 5-fluorouracil and gemcitabine) by boosting their energy metabolism and suppressing DNA damage and cell death. NMN had the strongest effect (Case Western Reserve University, 2026).
The lead researcher, Jordan Winter, was careful about scope: the study "does not suggest these supplements are dangerous for healthy people," but it raises "a potentially concerning role for NAD+-boosting supplements in the context of an active cancer, especially when used in conjunction with chemotherapy." It wasn't a human trial. It's still a clear reason for anyone with a cancer diagnosis to clear any NAD+ product with their oncologist first.
Pregnant or breastfeeding women. There's no safety data for NAD+ or its precursors in pregnancy or lactation. No data means no reassurance.
People with liver disease, or anyone tempted by mega-doses. High-dose nicotinamide, one of the pieces oral NAD+ breaks into, has a documented ceiling. Older reports linked 3 to 9 grams a day to liver injury, and acute doses in the gram range caused headache, nausea and dizziness (Hwang & Song, 2020). For scale, a 500 mg serving of NAD+ contains about 92 mg of nicotinamide by molecular weight, even if every molecule were broken down.
People on blood thinners, if the formula contains resveratrol or quercetin. Many NAD+ products, including Soleu's, pair NAD+ with those polyphenols. Memorial Sloan Kettering notes that resveratrol "may increase your risk of bleeding" with blood thinners such as warfarin, and that it inhibits platelet aggregation (MSKCC). That caution comes from the added ingredients, not from NAD+.
Anyone with surgery coming up. For the same bleeding reason, stop formulas containing resveratrol ahead of a procedure unless your surgeon says otherwise.
What Not to Mix With NAD+
There's no long list of documented drug interactions for NAD+ itself, partly because it has been studied so little in pill form. The combinations worth avoiding or discussing first are:
- Chemotherapy. For the reasons above.
- Anticoagulants and antiplatelet drugs (warfarin, clopidogrel, daily aspirin), when your NAD+ product includes resveratrol or quercetin.
- Drugs cleared by the liver's CYP enzymes, again when resveratrol is in the formula. At 1 gram a day for four weeks, resveratrol inhibited CYP3A4, CYP2D6 and CYP2C9 activity in healthy volunteers (Chow et al., Cancer Prevention Research, 2010). That's a much higher dose than most supplements contain, but it's worth mentioning to your pharmacist.
- Other B3 products. Doubling up on niacin, nicotinamide, NMN and NR at once pushes you into dose territory nobody has tested.
Best Time to Take NAD+, and How Long Before It Works
Most labels, Soleu's included, suggest the morning. The evidence for any particular time is thin, and the one trial that tested timing directly leans the other way.
In a 12-week randomized trial, 108 older Japanese adults took 250 mg of NMN or placebo either before noon or in the afternoon. The afternoon NMN group showed the largest effect sizes for lower-limb function on a sit-to-stand test and for reduced drowsiness (Kim et al., Nutrients, 2022). Two caveats: it tested NMN, not NAD+, and the sit-to-stand scores improved in every group, including placebo.
The practical answer: pick a time you'll stick to, take it with food, and move it earlier if you notice it affecting your sleep. Consistency matters more than the clock.
As for how long it takes: blood NAD+ rises quickly. In the NR trial, it rose significantly within two weeks and stayed up through eight weeks. Whether you feel anything is a separate question. Most trials run 8 to 12 weeks, and subjective effects on energy or fatigue have been inconsistent. A fair evaluation window is two to three months of daily use. Rising blood levels are something you can measure; how much difference you notice varies from person to person.
Where Soleu's NAD+ Formula Fits
Soleu's NAD+ formula pairs NAD+ with two polyphenols, so its safety profile depends on all three ingredients, not just the NAD+.
NAD+ Supplement with Resveratrol & Quercetin
Per two-capsule serving: 500 mg NAD+, 250 mg quercetin dihydrate, and 150 mg resveratrol (98%, from Japanese knotweed root). No nicotinic acid, so no niacin flush. 60 vegetable capsules, 30 servings, with every dose printed on the label.
See the full ingredient panelThe formula itself hasn't been tested in its own clinical trial, and nothing above should be read as saying it has. The evidence discussed here comes from studies of related compounds. The practical cautions follow from the ingredients: talk to your doctor first if you're on a blood thinner (because of the resveratrol and quercetin), in cancer treatment, pregnant, or breastfeeding. Take it with breakfast if your stomach is sensitive.
Frequently Asked Questions
How long do NAD+ side effects last?
With IV NAD+, reactions like cramping, nausea and chest pressure typically occur during the infusion and ease when the drip is slowed or stopped. With capsules, the mild stomach upset some people notice tends to settle when the dose is taken with food. Anything that persists is worth raising with a doctor.
Does NAD+ cause weight gain?
Weight gain hasn't shown up as a side effect in the capsule trials reviewed here. In the 1,250 mg NMN safety trial, body composition stayed within normal variation over four weeks. There's also no good evidence that NAD+ products cause weight loss.
Is NAD+ similar to Ozempic?
No. Ozempic (semaglutide) is a prescription drug that mimics the gut hormone GLP-1 to reduce appetite and regulate blood sugar. NAD+ is a coenzyme involved in cellular energy metabolism. They work through unrelated mechanisms, and NAD+ supplements are not a weight-loss drug.
Can NAD+ affect your heart or blood pressure?
The faster heart rate and chest pressure reports come from IV infusions. Capsule trials of NMN and NR haven't flagged heart or blood pressure problems, but they were small and short. If you have a heart condition or take cardiovascular medication, check with your cardiologist first.
Is it safe to take NAD+ every day?
Daily use is what the precursor trials tested, for up to 24 weeks, without an increase in adverse events versus placebo. Beyond that, there isn't long-term data for any NAD+ product. Daily use for months is reasonably supported; daily use for years hasn't been studied.
Are there NAD+ side effects specific to women?
The trials above enrolled both men and women and didn't report sex-specific side effects. The real gap is pregnancy and breastfeeding, where there's no safety data at all, so NAD+ products are best avoided then.
Do NAD+ side effects go away if you keep taking it?
No trial has tracked this directly. Mild stomach effects often improve once the dose is taken with meals. If a side effect is getting worse rather than better, stop taking the product.
The Bottom Line
Most of what you read about NAD+ side effects describes IV drips, where a large dose goes straight into a vein. Run fast, those infusions reliably cause cramping, nausea and chest pressure. Run slowly, over six hours, they can be tolerated without incident.
Capsules are a different situation. Oral NAD+ is largely broken down into precursors before it's absorbed, and precursor trials in hundreds of adults show side effect rates no different from placebo over periods of up to 24 weeks. The caveats are that the data is short-term, no oral NAD+ trial has been published yet, and anyone in cancer treatment, pregnant, or on blood thinners should check with a doctor first.
Related Reading
- NAD+ and Resveratrol: Why the Pairing Outlived the Hype: why the two are combined, and what the human trials show.
- Can You Take Quercetin With NAD+? The Science of Synergy Explained: CD38, the enzyme that breaks NAD+ down, and why quercetin is in the stack.
- NMN Benefits: What Does the Science Actually Say in 2026?: the human trials on the most-studied NAD+ precursor.
Sources
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- Conze D, Brenner C, Kruger CL. Safety and metabolism of long-term administration of NIAGEN in a randomized, double-blind, placebo-controlled clinical trial of healthy overweight adults. Sci Rep, 2019. PMC6611812
- Fukamizu Y, et al. Safety evaluation of β-nicotinamide mononucleotide oral administration in healthy adult men and women. Sci Rep, 2022. PMC9400576
- Alegre GFS, Pastore GM. NAD+ precursors NMN and NR: potential dietary contribution to health. Curr Nutr Rep, 2023. PMC10240123
- Poljšak B, et al. Current uncertainties and future challenges regarding NAD+ boosting strategies. 2022. PMC9495723
- Grant R, et al. A pilot study investigating changes in the human plasma and urine NAD+ metabolome during a 6 hour intravenous infusion of NAD+. Front Aging Neurosci, 2019. PMC6751327
- Reyna K, et al. Intravenous infusion of NAD+ versus nicotinamide riboside: a retrospective tolerability pilot study in a real-world setting. Front Aging, 2026. doi:10.3389/fragi.2026.1652582
- Case Western Reserve University. New research reveals dangers of "anti-aging" supplements in cancer protection. April 2026. case.edu
- Hwang ES, Song SB. Possible adverse effects of high-dose nicotinamide: mechanisms and safety assessment. Biomolecules, 2020. PMC7277745
- Kim M, et al. Effect of 12-week intake of nicotinamide mononucleotide on sleep quality, fatigue, and physical performance in older Japanese adults. Nutrients, 2022. PMID 35215405
- Chow HH, et al. Resveratrol modulates drug- and carcinogen-metabolizing enzymes in a healthy volunteer study. Cancer Prev Res, 2010. PMC2933312
- Memorial Sloan Kettering Cancer Center. Resveratrol (About Herbs). mskcc.org
- ClinicalTrials.gov. NCT07692633: absorption, safety, and efficacy of an oral NAD+ supplement in healthy adults. clinicaltrials.gov