NMN and NR Side Effects, Adverse Events, and What Happens When You Stop

What Are NMN and NR, and Why Do Women Take Them?

NMN and NR are two forms of vitamin B3 that your body converts into NAD+ (nicotinamide adenine dinucleotide), a coenzyme central to mitochondrial energy production, DNA repair, and cellular metabolism. NAD+ levels fall with age, and in women that decline appears to accelerate around perimenopause.

Women reach for NMN or NR most often for energy, cognitive sharpness, metabolic support, and skin quality. The compounds are also being studied in the context of PCOS-related insulin resistance, perimenopausal fatigue, and fertility preservation, though evidence for most of these applications is early-stage.

Understanding side effects matters here because these supplements are widely used, marketed aggressively, and taken for months or years without structured medical oversight. The following sections walk through what the human trial data actually show, what the FDA's postmarket safety database contains, and what women at different life stages should weigh before starting or stopping.

Common Side Effects Seen in Clinical Trials

Most side effects reported in NMN and NR trials are mild, transient, and dose-related. They rarely lead participants to stop.

Gastrointestinal Effects

GI complaints are the most frequently reported side effect across both compounds. In the first published placebo-controlled NMN trial by Igarashi et al. (2022), 250 mg per day of oral NMN in healthy older adults over 12 weeks produced no clinically significant adverse events and no meaningful difference in GI complaints versus placebo. At higher doses, the picture shifts.

A phase I safety trial of NR by Trammell et al. (2016) and a subsequent randomized crossover study by Dollerup et al. (2018) documented mild nausea and loose stools at doses of 2,000 mg per day, with most participants tolerating 1,000 mg without complaint. A 12-week double-blind trial in obese men and women (Dollerup et al. 2018) reported that nausea occurred in roughly 10% of participants at the higher dose range.

Flushing and Skin Effects

Unlike nicotinic acid (niacin), NMN and NR carry a far lower flushing risk because they do not directly activate the GPR109A receptor responsible for niacin flush. Mild facial warmth has been reported anecdotally and in a minority of trial participants, but it is not a consistent finding across placebo-controlled studies. If you experience significant flushing, consider whether your supplement contains any added niacin.

Fatigue and Sleep Disturbance

A small number of participants in NMN trials report an initial period of fatigue or altered sleep within the first week of use. The Igarashi 2022 trial did not identify sleep disruption as a statistically significant finding. Fatigue as an initial effect may reflect the body's adaptation to shifting NAD+ metabolite ratios, but this is speculative, and no mechanistic data in humans confirm that explanation.

Less Common and Rare Adverse Events

Elevated Liver Enzymes

Two participants in a Japanese NMN trial showed transient elevations in alanine aminotransferase (ALT) that resolved without intervention. The trial authors did not attribute causation definitively. Women with pre-existing non-alcoholic fatty liver disease, a condition strongly associated with PCOS and insulin resistance, should have baseline liver function checked before starting high-dose NAD precursors.

Changes in Blood Pressure

The CHROMADEX-funded ELYSIUM trial and the Brigham and Women's Hospital NR study (Martens et al. 2023) assessed cardiovascular parameters. In the Martens trial, 500 mg per day of NR over 12 weeks in older adults (mean age 71) produced no significant change in blood pressure versus placebo. Women on antihypertensive medications should monitor blood pressure when starting any NAD precursor, as preclinical data suggest NAD+ can influence vascular tone.

Homocysteine Elevation

This is the adverse effect with the clearest mechanistic explanation. Both NMN and NR are metabolized via pathways that generate methylation byproducts. Dellinger et al. (2017) documented homocysteine elevation in participants taking NR at 1,000 mg per day over 6 weeks. Elevated homocysteine is a known cardiovascular and pregnancy risk factor. Women with MTHFR variants, a history of recurrent pregnancy loss, or cardiovascular disease should discuss homocysteine monitoring with their clinician before using NAD precursors long term.

Blood Glucose Effects

Dollerup et al. (2020) found no improvement in insulin sensitivity in obese adults taking NR 2,000 mg per day for 12 weeks, and fasting glucose was unchanged. Women with PCOS who take NMN or NR hoping for insulin-sensitizing effects should know the evidence for this specific benefit remains unproven in the populations most relevant to them.

Does Stopping NMN or NR Cause a Withdrawal Syndrome?

No. There is no documented withdrawal syndrome associated with discontinuing NMN or NR in any published human trial, case series, or FAERS analysis as of mid-2025.

This deserves a plain explanation. Withdrawal syndromes arise when a substance creates physiological dependence, meaning the body down-regulates its own production of a molecule in response to exogenous supply, and then experiences deficit symptoms when supply is removed. NMN and NR supplement endogenous NAD+ synthesis. The question of whether supplementation suppresses the body's own NAD+ biosynthetic pathways (particularly the de novo tryptophan-to-NAD+ pathway and the Preiss-Handler pathway) is biologically plausible but has not been shown to cause clinically meaningful rebound NAD+ deficiency after stopping.

A 12-week trial by Igarashi et al. (2022) did not include a formal discontinuation-phase assessment. The Martens NR trial (Martens et al. 2023) similarly did not report rebound symptoms after the study period. No participant in any published NMN or NR trial has been described as experiencing medically significant symptoms upon stopping.

What Women Report When They Stop

In online communities and patient forums, some women describe a return of fatigue, brain fog, or reduced exercise tolerance within one to four weeks of stopping NMN or NR. This is almost certainly a return of baseline symptoms rather than pharmacological withdrawal, particularly for perimenopausal women whose underlying NAD+ trajectory was declining before they started the supplement. Distinguishing returning baseline symptoms from true pharmacological discontinuation effects requires a carefully designed placebo-controlled trial that does not yet exist.

Should You Taper?

No published guideline recommends tapering NMN or NR. Stopping abruptly is what every clinical trial has done by design at study end, with no documented harm. If you want to stop, you can do so without a taper.

Life-Stage Considerations

Reproductive Years

Data in women of reproductive age are genuinely thin. The Igarashi 2022 and Dollerup 2018 trials enrolled predominantly older adults. Women in their twenties and thirties who take NMN or NR for energy or skin benefits are doing so on extrapolated, not directly studied, evidence. Cycle-phase effects on NAD+ metabolism have not been studied in humans.

PCOS

Women with PCOS have documented mitochondrial dysfunction and altered NAD+ metabolism compared to age-matched controls, based on preclinical and small observational data. A 2021 cell and animal study suggested NMN may improve oocyte quality in aged mice by restoring mitochondrial function. No adequately powered human RCT in women with PCOS has replicated this. Extrapolating mouse oocyte data to human PCOS fertility outcomes is a significant inferential leap.

Perimenopause and Postmenopause

This is the life stage with the most relevant, though still limited, human data. The Igarashi 2022 trial included postmenopausal women and found improvements in muscle function and no significant adverse events at 250 mg per day. The Martens et al. 2023 NR trial in older adults similarly found a benign safety profile. Perimenopausal women experiencing fatigue and cognitive changes may be the group with the most biologically plausible rationale for NAD+ supplementation, but the evidence base does not yet support strong efficacy claims.

Women taking hormone therapy (HT) for menopause symptoms should be aware that no drug-interaction studies between estrogen-containing HT and NMN or NR have been published. This is a genuine evidence gap.

Pregnancy and Lactation Safety

NMN and NR should not be used during pregnancy or breastfeeding. This is not a precautionary formality. It reflects a complete absence of human safety data.

Pregnancy

No published human trial has enrolled pregnant women. No prospective pregnancy registry data exist for NMN or NR. Animal reproductive toxicology studies are not publicly available for NMN. NR has been studied in a mouse model of mitochondrial disease where it showed some protective effects in pups, but this cannot be generalized to human pregnancy safety. Because NAD+ is involved in neural tube development, DNA repair, and placental function, it is biologically plausible that altering NAD+ precursor availability during pregnancy has effects, positive or negative, that have not been characterized.

The FDA has not assigned NMN a pregnancy category because it is regulated as a dietary supplement, not a drug. There is no Category A, B, C, D, or X designation to rely on. The appropriate clinical standard is: if you are pregnant, stop and do not restart until after delivery and weaning.

Women who are actively trying to conceive face a more nuanced question. NAD+ precursors are being researched in the context of egg quality in older reproductive-age women, and some fertility specialists discuss them in this context. If you are trying to conceive, this is a conversation to have with your reproductive endocrinologist, not a decision to make based on supplement marketing.

Contraception Note

NMN and NR are not known teratogens in the formal pharmacological sense, and they do not require a specific contraception protocol like isotretinoin or thalidomide. Still, given the absence of human pregnancy data, women of reproductive age who want to take these supplements should use reliable contraception if pregnancy is not desired, as a standard precaution when any agent with incomplete reproductive safety data is taken long term.

Lactation

No human milk transfer data exist for NMN or NR. Nicotinamide (a related B3 metabolite) does transfer into breast milk, which is not inherently harmful at physiological levels, but pharmacological doses of NAD+ precursors represent a different exposure picture. In the absence of data, avoid use while breastfeeding.

Drug and Supplement Interactions

Published interaction data for NMN and NR are sparse. Several interactions are biologically plausible and clinically worth knowing.

Metformin: Metformin, widely used in women with PCOS and type 2 diabetes, inhibits mitochondrial complex I and has been shown to blunt NAD+ metabolism in some contexts. A 2023 study published in Nature Aging found that metformin may attenuate some of the metabolic effects of NMN, though this finding is preliminary and the clinical significance is uncertain.

Resveratrol: Often co-marketed with NMN as a sirtuin-activating stack. No human interaction trial has been conducted. The combination is pharmacologically uncharacterized.

Alcohol: Ethanol and NMN share NAD+-dependent metabolic pathways. Heavy alcohol use while taking NAD+ precursors has not been studied. Moderate alcohol use is unlikely to cause a significant interaction, but the data do not exist to confirm this with confidence.

What the FDA's Adverse Event Reporting System Shows

FAERS (the FDA Adverse Event Reporting System) contains a small number of case reports mentioning NMN and NR as suspect or concomitant agents. No serious adverse event signal, defined as death, hospitalization, life-threatening reaction, or congenital anomaly, has been identified in publicly available FAERS data as of mid-2025. The absolute number of reports is low relative to the volume of supplement use, which could reflect true safety, underreporting, or both. FAERS reports are not verified, and the database does not establish causation.

The FDA's 2022 new dietary ingredient (NDI) objection to NMN placed it in a regulatory gray zone in the United States. NR (sold commercially as Niagen, among other brand names) does not face the same NDI dispute and remains a lawfully marketed dietary supplement.

Regulatory and Quality Concerns Specific to Women

Supplement quality control directly affects safety. Adulteration, mislabeled doses, and contamination are documented across the supplement industry. Women who are pregnant, planning pregnancy, or managing a chronic condition like PCOS or thyroid disease should prioritize products with third-party testing from NSF International, USP, or Informed Sport. A 2023 independent analysis of commercially available NMN products found that actual NMN content ranged from 0% to 107% of label claim, meaning the dose you think you are taking may bear no relationship to what is in the capsule.

Who This Is Right For and Who Should Be Cautious

Women for whom a cautious trial may be reasonable:

• Postmenopausal women without active cancer, liver disease, or pregnancy, interested in metabolic or muscle support, who understand the evidence limitations
• Perimenopausal women with documented fatigue who have ruled out thyroid, iron-deficiency, and hormonal causes first
• Women over 40 discussing oocyte quality with a reproductive endocrinologist who specifically recommends it

Women who should not take NMN or NR without specific specialist guidance:

• Pregnant women (avoid entirely)
• Breastfeeding women (avoid entirely)
• Women with a personal or family history of hormone-sensitive cancers, because NAD+ plays a role in PARP-mediated DNA repair and the oncological implications of pharmacological NAD+ supplementation are not established
• Women with active liver disease or significantly elevated transaminases
• Women on chemotherapy or PARP inhibitors (direct mechanistic conflict)