Nicotinamide riboside (NR), sold as Niagen and Tru Niagen, is one of the most popular longevity supplements on the market. It has now faced its largest test in a neurological disease, and it lost. In the phase 3 NOPARK trial, published in JAMA in October 2026, people with early Parkinson disease who took NR did slightly worse than those on placebo. The effect was small, but the direction was the opposite of what the field hoped for.
What the trial actually did
NOPARK was a randomized, double-blind, placebo-controlled phase 3 trial run at 11 centers in Norway.
- Who: Adults aged 35 or older, diagnosed with Parkinson disease within the previous 2 years, Hoehn and Yahr stage below 3, abnormal dopamine transporter scintigraphy confirming loss of dopaminergic nigrostriatal neurons, and stable dopaminergic treatment.
- Sample size: 537 people were screened and 410 were randomized between May 2020 and June 2024. Of these, 393 were included in the primary analysis.
- Participants: Mean age was 65.6 years (SD 9.4), and 34% were female.
- Intervention: Oral NR at 500 mg twice daily (1,000 mg/day) or matching placebo, for 52 weeks.
- Primary outcome: Change in total MDS-UPDRS (parts I–III) from baseline to week 52. The scale runs from 0 to 236, and higher scores mean worse disease.
Final follow-up finished in June 2025. The trial is registered as NCT03568968.
The headline numbers
At week 52, the total MDS-UPDRS score rose by 2.45 points (95% CI 0.80–4.10) in the NR group. In the placebo group it fell by 0.27 points (95% CI −1.95 to 1.40).
The adjusted mean difference was 2.72 points (95% CI 0.47–4.98; P = .02), favoring placebo.
The non-motor symptom burden told a similar story. On the Non-Motor Symptoms Scale (range 0–360), NR was associated with a worse score, with an adjusted mean difference of 4.22 points (95% CI 1.07–7.37; P = .009).
Why "worse" needs context
This is not a story of patients being badly harmed. The investigators used published thresholds for clinically important change on the MDS-UPDRS: 6.7 points for improvement and 5.2 points for worsening. The 2.72-point gap is statistically significant, but it sits well below the worsening threshold. Even the upper end of its confidence interval (4.98) falls short of 5.2.
Four of the five prespecified key secondary outcomes showed no significant difference. Those were MDS-UPDRS parts I, II and III, and the dopamine transporter imaging findings. The only one that separated the groups was the non-motor score.
The most defensible reading is that NR did not help and was associated with modestly worse scores. The authors conclude it did not improve clinical outcomes and was associated with worse outcomes than placebo.
The safety twist
One finding runs against the "NR did worse" narrative. Serious adverse events occurred in 17 of 205 participants (8.3%) on NR and 29 of 205 (14.1%) on placebo in the safety population. So NR was not associated with more serious adverse events. If anything, it was associated with fewer. The study doesn't explain this gap, and it shouldn't be taken as evidence that NR protects against anything.
Why this result carries weight
The hope for NR in Parkinson's came from preclinical work and smaller early studies, including the earlier NADPARK work from the same Norwegian group. Those studies suggested NR could raise NAD+ levels and might influence brain metabolism. They were small and not designed to prove clinical benefit, and NOPARK was the confirmatory test.
Credibility is also worth noting. Several of the investigators hold patents on NR for Parkinson disease, licensed to Niagen Bioscience (formerly ChromaDex), according to the trial disclosures summarized in the source material. Researchers with a stake in a positive outcome reported a negative one anyway, which lends the result more weight. The design was also strong: double-blind, placebo-controlled, imaging-confirmed diagnosis, and a pre-specified primary endpoint.
What this means for you
- Don't self-treat with NR. The best available trial found no benefit and a slight signal toward worse outcomes at 1,000 mg/day for one year.
- If you are already taking NR, talk to your neurologist before deciding what to do. Don't stop or change prescribed medications on your own.
- Supplements are not a substitute for dopaminergic therapy or standard care.
If you take NR or NMN for general longevity:
- This was a disease trial in people with early Parkinson's, not healthy users. It does not show that NR harms healthy people.
- It does weaken the broader "raise NAD+ and protect the brain" story. If NR can't help even in a disease where NAD+ metabolism was a prime target, claims about neuroprotection in healthy people have less support.
- NMN was not tested here, so these results can't be directly applied to it. The same biological rationale applies, though, and the same skepticism is reasonable.
- Dose and timing: the trial used 500 mg twice daily for 52 weeks. Many commercial products use lower doses, so this trial doesn't map neatly onto typical supplement use. It provides no basis for recommending any dose or schedule.
Who might reasonably skip NR: anyone with Parkinson disease or a strong family history who is considering it as a preventive or disease-modifying step, and anyone buying it primarily for brain protection.
Who it leaves open: people taking it for other reasons, who should treat the evidence as unsettled, not proven. Discuss it with a clinician, especially if you have chronic illness or take other medications.
Bottom line
NOPARK is a rare case where a popular supplement was tested at scale in a disease its early data seemed to favor, and it came up short. The effect was modest and below clinical thresholds, serious adverse events were lower on NR, and the study is specific to early Parkinson's. But as a disease-modifying treatment, NR did not deliver.
