Does Nicotinamide Riboside Cause the Niacin Flush?

No, not the way niacin does. Niacin flushes through a skin receptor that NR does not appear to use. The largest NR trial we read recorded no flushing, but no trial measured it with a validated tool, and two small studies logged self-reported flushes. If you flush after an NR product, check the label for niacin first.

The short answer

NR does not appear to cause the classic niacin flush. Niacin flushes through a skin receptor, GPR109A, that nicotinic acid binds and that NR is not known to bind. No human NR trial measured flushing with a validated tool.

Two small trials logged self-reported flushing on NR. In one, two of 12 people reported flushing at a single 300 mg dose. In the other, three people reported flushing on a 1,000 mg a day crossover, and two of them were on placebo at the time.

The largest trial we read (140 adults, eight weeks, up to 1,000 mg a day) recorded no flushing reports at all. If you flush after an NR product, check the label for niacin or nicotinic acid first.

Why isn't the answer simple?

For the wider picture, see the NAD+ longevity guide. The short version is that the answer depends on which molecule you mean.

The NIH uses "niacin" as a broad name. Its fact sheet says niacin is the generic name for nicotinic acid, nicotinamide and related derivatives, "such as nicotinamide riboside." By that usage, NR is a niacin. The flush, however, belongs to one form. The same fact sheet says supplemental nicotinic acid can cause skin flushing, and that nicotinamide does not, because of its slightly different chemical structure.

Here is the detail most people miss. The NIH sets the adult upper limit for supplemental niacin at 35 mg a day, and it says that limit is based on the levels associated with skin flushing. The flush is what the ceiling was built around. The fact sheet says 30 to 50 mg or more of nicotinic acid typically causes flushing, with redness on the face, arms and chest and a burning, tingling or itching feeling.

The mechanism is mapped in some detail. Nicotinic acid activates GPR109A, a receptor on immune cells in the skin, which releases prostaglandins D2 and E2 and widens small blood vessels. In a 2005 mouse study, animals without the receptor did not flush from nicotinic acid. When researchers transplanted normal bone marrow into those animals, the flush came back, which points at skin immune cells rather than the blood vessels themselves (Benyó et al., 2005). A 2012 review places the prostaglandin release in Langerhans cells and keratinocytes, through COX-1 and COX-2 (Hanson et al., 2012).

No study we found tests NR at that receptor. A 2007 review by Penberthy states that, among the NAD precursors, only nicotinic acid specifically activates GPR109A (Penberthy, 2007). So the case that NR does not cause the flush rests on receptor chemistry and trial data, not on a direct receptor test.

Milligrams do not compare directly either. The 30 to 50 mg threshold refers to nicotinic acid. The NR trials gave 100 to 3,000 mg a day of NR, which is a different molecule.

There is one route by which NR could reach the flush pathway. Gut bacteria can convert NR into nicotinic acid. A 2026 trial found that human gut microbes did this in lab fermentation, and that urine markers of nicotinic acid metabolism rose after NR (Christen et al., 2026). The authors did not detect a rise in nicotinic acid in blood. Nobody has measured whether gut-made nicotinic acid reaches a flush-causing level. NMN, a related precursor, has its own monograph, and the NMN and NR comparison sets the two side by side.

What did the NR trials record about flushing?

We read ten human NR studies for this page. Eight were checked in full text. Two, Brakedal et al. (2022) and Li et al. (2023), were read from the abstract only, and the page says so where it matters. For the dose each study used, see NMN and NR doses compared with the trials.

Trammell et al., 2016 (PMID 27721479). Twelve healthy adults, six men and six women aged 30 to 55, took single doses of 100, 300 or 1,000 mg of NR on separate days, seven days apart, in random order. Participants and investigators did not know which dose was which. The study measured blood NAD metabolites and asked participants to report discomforts. Two people reported flushing at 300 mg and not at 100 or 1,000 mg, and two reported feeling hot at 1,000 mg. There were no serious adverse events and no dose-dependent events over 36 days. The same paper includes a single-person pilot in which one participant flushed on 250 mg of niacin and reported no flushing during seven days of 1,000 mg of NR. The limit that matters: flushing was self-reported, and the authors say a validated flushing questionnaire will be needed. Two authors list ChromaDex, the NR manufacturer, as an affiliation.

Martens et al., 2018 (PMID 29599478). Thirty healthy middle-aged and older adults took part in a two-period crossover, six weeks on NR and six weeks on placebo, with NR at 500 mg twice a day, or 1,000 mg a day. The study measured blood NAD metabolism and adverse events. Fourteen adverse events were reported by seven of the 30 people, all mild, and the authors call NR well tolerated, with no serious events. Three participants reported flushing. Two of them were taking placebo when they reported it, and the authors read this as no sign that NR itself causes flushing. A skin rash appeared during the placebo period, and two people stopped for side effects, both on placebo: one for headache and one for a rash. The limit that matters: adverse events were self-reported, with no flushing-specific measure.

Conze et al., 2019 (PMID 31278280). 140 overweight but otherwise healthy adults aged 40 to 60 were randomized to placebo or 100, 300 or 1,000 mg of NR a day for eight weeks, after a two-week run-in. 133 finished. Whole-blood NAD rose 22, 51 and 142 percent at day 14 in the three dose groups. Flushing was one of the named adverse-event terms the trial coded. The trial recorded 95 adverse events in 61 people, no serious ones, and no flushing reports. The limits: adverse events came from participant diaries and visit questions, with no flushing-specific measure; participants were asked to avoid foods rich in tryptophan and niacin; and two authors list ChromaDex affiliations. The trial excluded pregnant or breastfeeding women and people taking blood-pressure or cholesterol medicines.

Berven et al., 2023 (PMID 38016950). Twenty adults with Parkinson's disease were randomized to 1,500 mg of NR twice a day (3,000 mg a day) or to placebo for four weeks. Investigators graded the adverse events. The NR arm had 25 adverse events and the placebo arm had 17, all mild, with no significant difference. One NR participant had a non-painful maculopapular rash, which the investigators judged unlikely to be caused by NR because the same rash had been treated before the trial. The authors say no painful flushing was reported. That is narrower than no flushing at all, because it covers only the painful kind. Two NR participants had asymptomatic slow heart rates. The limits: 20 people for four weeks, and the study drug was supplied by ChromaDex.

Christen et al., 2026 (PMID 41540253). Sixty-five healthy adults aged 18 to 50 took NR at 1,000 mg a day, NMN at 1,000 mg a day, nicotinamide at 500 mg a day, or placebo for 14 days in an open-label study. Blood NAD rose about twofold with NR. The authors list three adverse events as probably related to the product. One was abdominal pain in a placebo participant, one was low blood pressure in an NR participant, and one was headache in an NMN participant. None was flushing, and the results text names no skin event. The limits: the open-label design, eleven of twelve authors with Nestlé affiliations, and a gut-conversion step tested in lab fermentation.

Five more trials were read as well. Dellinger et al. (2017, PMID 29184669) tested a pterostilbene combination in 120 adults aged 60 to 80. Its only skin-type event was a mild itch, judged possibly related and recorded in the placebo group. Remie et al. (2020, PMID 32320006) gave 1,000 mg a day to 13 adults for six weeks and reported no adverse events or side effects. Martens et al. (2026, PMID 42478598) gave 1,000 mg a day for 12 weeks to 52 adults with mild cognitive impairment, and 42 finished. The narrative names nausea, diarrhea and mild headache, and does not mention flushing. Brakedal et al. (2022, PMID 35235774) gave 1,000 mg a day for 30 days in Parkinson's disease. The abstract calls NR well tolerated and does not mention flushing. Li et al. (2023, PMID 37271226) tested six combined formulas, each with 1 g of a different NAD precursor, in a one-day study. Its abstract says niacin caused a flushing reaction. The abstract gives no flushing result for the NR formula.

Evidence grades, per outcome

Which situation applies to you?

If you flush after an NR product, the label is the first thing to check. Niacin is common in multivitamins and B-complex products, and NR is not labeled as niacin. Note the dose, the time and the product, and bring them to your prescriber if the reaction keeps happening.

How do you read the label, and what should you avoid?

On the Supplement Facts panel, look for niacin, nicotinic acid and inositol hexanicotinate. Products sold as flush-free often use inositol hexanicotinate, and the NIH says its absorption averages about 30 percent lower than nicotinic acid or nicotinamide. The label checklist walks through the rest of the panel for NR and NMN products.

Nicotinamide does not flush. The NIH's concern with it is different: nausea, vomiting and signs of liver toxicity can occur at 3,000 mg a day. Some products list it beside NR, so read the milligrams.

The trials gave 100 to 3,000 mg of NR a day, and most gave 1,000 mg. None of the trials we read tested a titration schedule, so there is no evidence that a slow start prevents flushing. For niacin, the NIH suggests taking it with food, raising the dose slowly, or waiting for tolerance to develop. Those tips come from niacin research, not NR research.

In the Conze trial, participants took their capsules after breakfast. None of the abstracts we read gives a reason for a particular time of day, so timing is not established. The Conze trial excluded pregnant and breastfeeding women, and no trial we read tested NR in children, pregnancy or nursing. Those groups have no safety data here.

When should you stop or ask someone?

Stop and call a clinician if a flush comes with a rash that spreads or does not fade, dizziness, fainting, or a headache with a fall in blood pressure. The NIH lists rash, dizziness and blood-pressure drop as the serious signs that come with niacin flushing, and the ACC/AHA advises stopping niacin for persistent, severe skin reactions. Those are niacin rules, and the NR trials did not test them.

Flushing with diarrhea, or flushing when you have taken no supplement, needs a clinician. The NIH lists facial flushing with diarrhea among the features of carcinoid syndrome, a tumor-related condition.

In the four-week trial at 3,000 mg a day, two participants had asymptomatic slow heart rates of 58 and 46 beats per minute. If you have a heart rhythm condition, ask before you start.

Do not change a prescription to fit a supplement. In the Parkinson's trial, the motor-score improvement came with a shorter gap since the last levodopa dose, and the authors could not rule out levodopa timing as at least a partial cause.

Product note

This page does not link a product. The trials used 100 to 3,000 mg of NR a day, and we have not verified a product that matches that range. The buying guide compares NMN and NR products and explains what to look for on a label.

Next reads

• Up: The NAD+ longevity guide places flushing alongside the rest of the NR and NMN evidence.
• Across: NMN and NR doses compared with the trials shows the dose each study used.
• Deeper: Nicotinamide riboside: the human NR trials has the full evidence table.
• Commercial: Our NMN and NR buying guide compares products on dose and label.

Related reading

• how tryptophan feeds the niacin story
• the historical story behind the niacin flush

More on NAD+ and Cellular Energy: The Complete Guide