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Safety

Does NMN cause diarrhea?

Written by the Full Measure editorial team, which sells supplements. Approved for publication by the Full Measure owners. Updated .

Drafted with AI assistance from the sources listed below. How we write these

Quick answer

In a 2026 systematic review, gut side effects were reported by 16 of 168 people taking NMN and 17 of 92 taking placebo, a difference that was not statistically significant. The review pooled gut effects as one group and did not report diarrhea alone. Anyone with a gut or liver condition should ask their doctor first.1

Key facts

  • A 2026 systematic review pooled 7 randomized trials: gut side effects occurred in 16 of 168 people on NMN and 17 of 92 on placebo or control, which is not a significant difference.1
  • The same review found no increase in overall, serious or withdrawal-related adverse events, or in the liver enzymes ALT and AST, at 250 to 2,000 mg a day for 14 days to 24 weeks.1
  • In a 12-week trial of 30 adults taking 250 mg a day, gut symptoms were reported by 3 of 15 on NMN and 2 of 15 on placebo.2
  • In a 4-week trial of 31 adults taking 1,250 mg a day, loose stool was reported once on NMN and once on placebo, both mild.3
  • For nicotinamide, the vitamin B3 form NMN is converted into, NIH says diarrhea was the most common effect of 500 to 1,500 mg a day in small studies of people on dialysis.4

What did the review of NMN trials find about gut effects?

A 2026 systematic review searched six databases up to May 2026 and pooled randomized trials of oral NMN against placebo or a control. Ten trials with 383 participants contributed to its safety analysis. For gut side effects, 7 trials reported data: 16 of 168 people taking NMN had one, against 17 of 92 in the comparison groups. The review calls that difference not significant, and it also found no significant rise in nervous system, skin or other adverse events.1

The review pooled gut events as one group, so it does not say how many were diarrhea, constipation or bloating. Its authors also say the evidence is dominated by small, short trials, which cannot rule out rare, delayed, long-term, high-dose or population-specific risks.1

What did individual NMN trials report about diarrhea and bloating?

In a 12-week trial of 30 healthy adults taking 250 mg a day, gut symptoms were listed together as abdominal pain, abdominal malaise, diarrhea, hunger, distension, belching or gas. They were reported by 3 of 15 people on NMN and 2 of 15 on placebo. One person on placebo left the study because of gut symptoms, and one person on NMN had abdominal pain that went away within 30 minutes. Employees of the NMN maker prepared the capsules.2

In a 4-week trial of 31 healthy adults taking 1,250 mg a day, five adverse events were recorded, and two were loose stool: one in the placebo group and one in the NMN group, both mild. The investigator judged none of the five related to the supplement. Five of the authors worked for the company that supplied the NMN.3

Does the vitamin B3 in NMN matter for the gut?

Europe counts NMN as a source of nicotinamide, so it adds to the vitamin B3 in multivitamins and in niacin, nicotinamide or nicotinamide riboside supplements.5

For nicotinamide itself, NIH's Office of Dietary Supplements says nausea, vomiting and signs of liver toxicity can occur at 3,000 mg a day. It adds that in several small studies of people on dialysis, the most common effects of 500 to 1,500 mg a day taken for several months were diarrhea and low platelet counts. Those studies tested nicotinamide in people on dialysis, not NMN in healthy adults, so they show what to watch for rather than what NMN does.4

What is not known about NMN and the gut?

Use for longer than 24 weeks has not been studied in trials, so long-term effects are unknown.1,5

A PubMed search for the NMN guide on October 7, 2026 found no trial comparing NMN taken with and without food. A search on October 11, 2026 for NMN in children or adolescents found no trial, and the European opinion covers adults only.1,5

Who should ask a doctor about NMN and gut symptoms?

  • Anyone with a gut or liver condition, before starting NMN.1
  • Anyone who takes a prescription medicine, including medicines for blood sugar, because insulin measured after lunch rose in healthy adults taking NMN in one study.6,7
  • Anyone who already takes niacin, nicotinamide or nicotinamide riboside, since the vitamin B3 adds up.5
  • Anyone who is pregnant, nursing or under 18, because the trials and the European opinion did not cover them.5,6

If diarrhea or stomach pain starts after you begin NMN and does not pass, tell your doctor which product you take and how much.2

Questions people ask

Does NMN cause diarrhea?

In a 2026 review of randomized trials, gut side effects were not significantly more common with NMN than with placebo, but the review did not report diarrhea on its own. Two trials listed loose stool or diarrhea among symptoms seen in both NMN and placebo groups.1,2,3

Does NMN cause constipation?

The 2026 review pooled gut effects as one group and found no significant difference between NMN and placebo, and it did not report constipation separately. Ask your doctor if a gut symptom starts or lasts after you begin NMN.1

Does NMN cause bloating?

In a 12-week trial of 30 adults taking 250 mg a day, one person on placebo left the study because of continuing abdominal bloating, and one person on NMN had mild stomach discomfort right after taking it that passed on its own.2

Does NMN cause headaches?

In the 12-week trial of 30 adults taking 250 mg a day, two people on placebo and none on NMN reported headache. The 2026 review found no significant rise in nervous system events, which were 11 of 145 on NMN and 7 of 69 in the comparison groups.1,2

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Sources

  1. Yang W, Huang J, Tang Z, Chen C, Sun Y. Safety and Metabolism-Related Outcomes of Oral Nicotinamide Mononucleotide Supplementation in Adults: A Systematic Review and Meta-Analysis. Nutrients. 2026;18(14):2251. Opened 2026-10-07.
  2. Okabe K, Yaku K, Uchida Y, et al. Oral Administration of Nicotinamide Mononucleotide Is Safe and Efficiently Increases Blood Nicotinamide Adenine Dinucleotide Levels in Healthy Subjects. Front Nutr. 2022;9:868640. Opened 2026-10-07.
  3. Fukamizu Y, Uchida Y, Shigekawa A, Sato T, Kosaka H, Sakurai T. Safety evaluation of β-nicotinamide mononucleotide oral administration in healthy adult men and women. Sci Rep. 2022;12(1):14442. Opened 2026-10-07.
  4. National Institutes of Health, Office of Dietary Supplements. Niacin: Fact Sheet for Health Professionals. Updated November 18, 2022. Opened 2026-10-07.
  5. EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA); Turck D, Bohn T, Cámara M, et al. Safety of beta-nicotinamide mononucleotide (β-NMN) pursuant the regulation (EU) 2015/2283 and the bioavailability of nicotinamide from this source in the context of Directive 2002/46/EC. EFSA J. 2026;24(5):e10007. Opened 2026-10-01.
  6. National Institutes of Health, Office of Dietary Supplements. Dietary Supplements: What You Need To Know. Fact sheet for consumers. Updated January 4, 2023. Opened 2026-10-07.
  7. Yamane T, Imai M, Bamba T, Uchiyama S. Nicotinamide mononucleotide (NMN) intake increases plasma NMN and insulin levels in healthy subjects. Clin Nutr ESPEN. 2023;56:83-86. Opened 2026-10-07.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.