NMN and NR Side Effects: Rare but Serious Adverse Events Explained

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Do NMN and NR cause serious side effects in trials?

The most detailed safety study randomized 31 healthy adults aged 20 to 65 to NMN 1,250 mg once daily or placebo for up to 4 weeks, double-blind. No severe adverse events were observed, and there were no changes beyond normal physiological variation in blood counts, blood chemistry, urine tests or body composition [1].

Longer, lower-dose studies point the same way. In a 12-week trial of 30 healthy adults, 15 received NMN 250 mg daily and 15 received placebo; no abnormalities appeared on physiological or laboratory testing and no obvious adverse effects were observed [5]. A dose-ranging trial in 80 middle-aged adults compared placebo with 300, 600 or 900 mg NMN daily for 60 days and reported no safety issues on adverse-event, laboratory and clinical monitoring [6].

For NR, a crossover trial randomized 30 older adults aged 55 to 79 (24 completed) and recorded 14 mild adverse events in seven participants, including nausea, flushing, leg cramps and bruising; no serious events occurred [3]. A 12-week trial randomized 40 obese men to NR 2,000 mg daily or placebo and reported no serious adverse events, with normal safety blood tests [7]. In a four-week trial of 20 people with Parkinson's disease, 10 received NR 3,000 mg daily and 10 received placebo; no moderate or severe adverse events were reported [2].

One unusual finding came from a 21-day crossover study of 12 men aged 70 to 80: four of them (33%) self-reported increased libido while taking NR and none on placebo, with no clinical adverse events reported [8].

How much can that safety record rule out?

The trials were small, 12 to 140 people, and short, up to about 12 weeks, so an uncommon harm or one that takes years to appear could not show up in them [4].

What about the cancer concern?

Cancer risk with chronic NAD+ boosting has been raised as a theoretical concern, and no human data were identified [4]. People with cancer were not included in the trials [4]. NAD+ is needed for cancer cell proliferation, which is one reason NAD metabolism is being studied as an anticancer target [11].

Do NMN and NR affect methylation?

Excess nicotinamide is cleared by methylation. In 12 older men, NR 1 g daily raised nicotinamide-methylation products about 5-fold in muscle, indicating clearance of excess nicotinamide through methylation [8]. In the 3,000 mg-per-day Parkinson's trial, NR recipients had a slight initial rise in serum homocysteine, and the authors judged the methyl donor pool intact [2]. Both measurements come from trials of 4 weeks or less.

Can NMN or NR hurt the liver?

None of the trials above reported a serious adverse event. Blood chemistry was unchanged beyond physiological variation in the 1,250 mg NMN safety trial [1] and normal in the 2,000 mg NR trial [7].

Nicotinamide is a different molecule and a breakdown product of these precursors. A 2000 review of high-dose nicotinamide reported reversible hepatotoxicity at very high doses, occasional minor liver enzyme abnormalities at the doses used for diabetes prevention studies, and called adult doses above 3 g per day a drug with toxic potential [12]. That review did not test NMN or NR, so it does not set a threshold for either supplement.

Do NMN or NR interact with prescription drugs?

No human drug-interaction study of NMN or NR was found in a PubMed search, so their interactions with prescription drugs remain unknown [4]. In NR-SAFE, 10 of 20 participants received 3,000 mg of NR daily and 10 received placebo for 4 weeks; an apparent improvement in MDS-UPDRS scores was also associated with a shorter interval since the last levodopa dose, so the clinical result is confounded [2].

Who was not included in the trials?

Pregnancy, breastfeeding, children, and people with cancer, kidney disease or liver disease were not included in the trials, so safety in these groups is unknown [4].

Are NMN and NR approved drugs?

Both are sold in the US as oral dietary supplements, and neither is an FDA-approved drug. No NAD+ precursor product is FDA-approved to treat aging or any disease [13].

FDA's response to a citizen petition about NMN, dated 2025-09-29, is reported to conclude that NMN is not excluded from the dietary supplement definition [13]. NMN is still a new dietary ingredient, so a maker must file an NDI notification or rely on a prior notification covering that supplier's ingredient before selling it [13]. For NR, FDA replied 'no questions at this time' to a 2016 GRAS notice for nicotinamide riboside chloride and stated it had not made its own GRAS determination [14].