Understanding NMN Safety: Potential Side Effects and Concerns

Effects of NMN supplements: What research tells us

A mix of rodent and human studies has raised approximately zero red flags when it comes to safety concerns (and tons of great news for fighting the hallmarks of aging). Let’s review:

• A human clinical toxicity study conducted at Keio University in 2020 specifically focused on safety and concluded that NMN can be safely administered to people. Study participants took a daily dose of 100, 250, or 500 mg of NMN and were monitored for 5 hours after each administration with no negative side effects on physiological measurements like heart rate or blood pressure.
• In 2021, a study looked at the effects of NMN and exercise on amateur runners over a six-week trial. There were three dosage groups of 300 mg, 600, and 1,200 mg per day. While this trial didn’t focus on safety, there were no negative side effects at any dosage. Incidentally, the biggest takeaway here was that aerobic capacity improved in the medium and high groups, which averages out to 900 mg daily as an optimal amount of NMN.
• Another 2021 study from the University of Tokyo looked at the impact of 250 mg of NMN daily for 12 weeks. There were a number of improvements noted, but again, no negative side effects.
• A study from the School of Medicine at Washington University also analyzed the effects of 250 mg of NMN per day, this time over a 10-week window. The older women who made up the participants in this trial had noticeable health changes for the better.
• One of the most recent clinical trials – results will be published in 2022 – administered placebo, 300, 600, and 900 mg doses to people in four groups. No signs of toxicity were observed at any amount, and those in the 900 mg group experienced the most positive effects.
• A 2022 safety evaluation of multiple clinical trials looked at the effects of taking 1,250 mg of NMN daily for four weeks on a group of healthy adult men and women. The results showed that this amount of NMN was safe to consume and did not cause any side effects or unwanted changes in their health.
• Specific to Wonderfeel, a 2025 paper investigated the user-reported benefits of close to 200 Youngr™ NMN users. Over two-thirds reported perceived improvements energy, cognition, sleep, and skin health. Non-causal adverse effects were reported in 1.5% of users.

Can I take 2,000 mg NMN?

A 2023 clinical trial led by longevity expert David Sinclair at Harvard Medical School looked at the effects of a daily 2,000mg dose of a stable NMN variant called MIB-626 on adults between the ages of 55 to 80 over a two-week period. Participants were randomized—some received 1,000mg once or twice daily while others received a placebo. Even at the highest dose, no serious side effects were reported, underscoring NMN’s excellent safety profile.

Rodent studies echo these findings, showing that even very high doses of NMN don’t trigger the sort of toxic reactions typically seen in other compounds. That’s notable, because a high dose of just about any drug on mice almost always causes immediate side effects. Consider it another layer of reassurance about NMN’s tolerability.

Sinclair himself has noted, “human studies with NAD boosters are on-going and so far, there has been no toxicity, not even a hint of it.” Wonderfeel’s own chief medical officer, Harvard-trained physician and research Dr. Andrew Salzman, further confirms that NMN is a very safe molecule for humans to take as a supplement.

Debunking myths: NMN and cancer concerns

There is no clinical evidence that NMN causes cancer. On the contrary, researchers have shown that NAD supplementation may help fight cancerous tumors by boosting the efficacy of immune cells. When immune cells are activated to fight off cancer, they consume more NAD—even while NAD in non-cancerous cells may likewise become depleted.This reinforces the idea that a decline in NAD can weaken anti-tumor immunity and may contribute to disease progression.

Treatments for cancer, including chemotherapy and radiotherapy, can affect DNA repair in cancerous and normal cells alike, which also leads to an increase in NAD consumption. In older adults, this dual depletion—from both aging and treatment—can be particularly concerning. A 2024 study looked at NAD concentrations in 99 patients with eight different types of cancer. Following surgery, NAD levels for most patients remained relatively stable, but decreased the following day and began exhibiting a recovery trend. But those with liver and pancreatic cancer had poor postoperative NAD recovery, and researchers noted the potential for a cancer type-specific influence on the metabolizing of NAD and the need for personalized NAD supplementation strategies.

However, it’s important to note the obvious here—cancer cells themselves require a lot of energy to grow and divide, and hence they demand more NAD. It’s been observed that various types of cancer cells rely on metabolic pathways which are regulated by NAD. In one small scale study, researchers fed nicotinamide riboside, or NR, to mice that have tumors and observed that both cancer and non-cancer cells consume NR as expected. A recent paper from 2022 explains this concept by examining the metabolic nutrition demand (not specific to NR), showing how healthy cells and cancer consume the same nutrients. While NAD precursors appear to be beneficial to cancer-fighting cells only, the conservative and medically responsible recommendation for anyone actively in treatment for cancer is to avoid taking NMN or NR until you’re free and clear of the disease. Even though NAD precursors may ultimately prove beneficial as part of post-treatment recovery or adjunctive therapy, the evidence isn’t there yet. Here at Wonderfeel, we err firmly on the side of caution and we don’t recommend taking NAD precursors at all if you have cancer and you’re currently in treatment.

On the other hand, if you’re concerned that NMN supplements might somehow increase one’s risk of cancer, that’s a different story. There is no evidence that NMN supplementation causes or promotes cancer in healthy individuals. And as another recent paper concludes, NMN supplementation may be employed as adjuvant therapies for fighting cancerous tumors.

Is NMN toxic to the liver?

The liver is an incredible, if wildly underrated, organ. But it’s just as susceptible to the ravages of time as the rest of us. Because its ability to metabolize substances declines with age, drug dosages for older adults are typically decreased. So what about NMN? Is NMN toxic to the liver, especially as we age? On the contrary, NMN has shown potential benefits for liver health, countering the very idea of toxicity. NMN supplementation aids in reducing both collagen deposits and problematic liver enzymes and prevents scar tissue build-up, which is crucial for maintaining liver function as we age. In a delightful twofer, promising research supports the role of NMN in enhancing liver health and aligns with Wonderfeel’s commitment to healthy aging and overall wellness.

Is NMN safe during pregnancy?

You really can’t be too cautious when you’re pregnant. After all, this is a life stage when you’re looking at soft cheeses with great suspicion. While research finds that NMN has been reported as effective for fertility treatment in some users, it’s important to proceed with caution when considering its safety during pregnancy.

Currently, there is no research available on the effects of NMN in pregnant individuals. We strongly recommend consulting with a healthcare professional before introducing new supplements of any kind during pregnancy, NMN included. That’s the safest, smartest way to make the right decisions for mom and baby alike.

Is NMN safe for dogs?

The effects of time are perhaps nowhere as clear as they are in man’s best friend. Anyone who has ever loved and lost a dog knows that their lives are far too short. And if NMN supplementation is so powerful for humans, is there a chance it could benefit our furry friends as well? The jury is still out, but recent research, including a study by Front Pharmacol, indicates that NMN can be well-tolerated by dogs when administered properly.

The research focused on the subacute toxicity of NMN in mice and beagle dogs, assessing its effects when administered orally. In this study, the dogs showed only mild increases in certain blood markers with no significant adverse effects, suggesting that NMN could be safe for dogs. Of course, every dog is unique, and we recommend consulting with your veterinarian before introducing any new supplement to your dog’s routine. Dogs can be sensitive to dietary changes, and talking it out with your vet ensures that any decision made is tailored to your pet’s specific health needs. Just like toting along compostable poop bags, it’s the responsible pet owner thing to do!

Evaluating the safety of long-term NMN supplementation

Research to date says yes, long-term NMN supplement is not only safe but well tolerated and effective. But “long term” itself is somewhat subjective—12 weeks? Twelve years? Fifty years? As NMN is the latest, greatest breakthrough in longevity medicine, we don’t yet have the insights that decades of research will bring. What we do have, however, are countless studies with the same conclusion regarding NMN’s high safety profile and the insights of brilliant scientific minds like Sinclair and Salzman. At the risk of repetition, let us revisit what Sinclair himself has said: “Human studies with NAD boosters are on-going and so far, there has been no toxicity, not even a hint of it.”

Making an informed decision: Is taking NMN safe for you?

The decision to take an NMN supplement is personal, and you’re wise to be thoughtful about whether it might benefit you. Beyond doing your due diligence, like you are right now, it’s a good idea to speak with a healthcare professional about whether supplementing is appropriate for you personally.

The takeaway on NMN safety

By all accounts, NMN supplementation is safe and well-tolerated for adults—and even dogs. Of course, we’re not suggesting that endless amounts of NMN are perfectly fine (read about the optimal dose here). While people have a tendency to assume that more is always better, moderation is almost always a wiser strategy. After all, too much of just about anything, even water, can be harmful. But, when it comes to NMN, the scientific research to date and leading authorities in the field of longevity science have all drawn the same conclusion—there is no evidence of any untoward side effects in reasonable doses, which means you can take your daily Wonderfeel NMN without worry. Wonderful news, isn’t it?