Vitamin B3 supplement fails to slow Parkinson's in a large trial

A popular "healthy ageing" supplement has failed to slow Parkinson's disease in the largest trial of its kind. People who took nicotinamide riboside, a form of vitamin B3, for a year did slightly worse than those on placebo.

The NOPARK trial, run at 11 hospitals in Norway, randomised 410 people with early Parkinson's. After 52 weeks, scores on the main Parkinson's rating scale had worsened by 2.45 points with the supplement and improved by 0.27 points with placebo. The adjusted difference of 2.72 points favoured placebo.

The results were published online in JAMA on 8 October 2026. The trial was led by Professor Charalampos Tzoulis of Haukeland University Hospital and the University of Bergen, with Brage Brakedal as first author.

Why vitamin B3 was tested

Nicotinamide riboside (NR) is converted in the body to nicotinamide adenine dinucleotide, or NAD. Cells need NAD to make energy, repair DNA and control inflammation. Levels decline with age, and NR is sold widely as a longevity supplement.

In Parkinson's, the mitochondria, the parts of cells that produce energy, are thought to work poorly in dopamine-producing nerve cells. Laboratory studies, including work in fruit flies, suggested that raising NAD might protect these cells, according to Parkinson's UK.

Two earlier small trials from the same Bergen group, NADPARK and NR-SAFE, found NR raised NAD in the brain and blood and was well tolerated over weeks. Exploratory results hinted at less inflammation, better energy metabolism and some improvement in movement, according to Cure Parkinson's. Parkinson's UK notes that those trials used much higher doses, up to 3,000 mg a day, over short periods.

The NOPARK trial

NOPARK (NCT03568968) was a randomised, double-blind, placebo-controlled phase 3 trial.

Of 537 people screened, 410 were randomised between May 2020 and June 2024. The primary analysis included 393. The average age was 65.6 and 34% were women.

The main measure was change in total score on parts I to III of the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS), which covers non-motor experiences, motor experiences of daily living and a motor examination. Higher scores mean more severe disease.

What the trial found

NR did not help. After 52 weeks:

• MDS-UPDRS total rose by 2.45 points with NR (95% CI 0.80 to 4.10)
• It fell by 0.27 points with placebo (95% CI -1.95 to 1.40)
• The adjusted difference was 2.72 points in favour of placebo (95% CI 0.47 to 4.98, p=0.02)

The difference was statistically significant but below the change usually considered clinically important for one person, according to the JAMA paper, which cites thresholds of 5.2 and 6.7 points.

Of five key secondary outcomes, four showed no difference. Non-motor symptoms worsened more with NR, by 4.22 points on the Non-Motor Symptoms Scale (p=0.009). Medscape reported that quality-of-life scores were also slightly lower with NR (p=0.02).

Dopamine transporter scans showed no difference, so the supplement neither slowed nor sped up loss of dopamine nerve endings on imaging.

It raised NAD, but not where it counted

NR did what it was expected to do in the blood. According to Medscape, blood NAD was 30 micromolar higher than with placebo (p<0.001). But brain scans in 159 participants showed a similar NAD to ATP ratio in both groups, suggesting there was no sustained change in brain energy metabolism over the year.

"NR clearly increased NAD metabolism, but this did not translate into clinical improvement," Professor Tzoulis said in a University of Bergen statement. "Our results therefore do not support NR as a treatment to slow Parkinson's disease."

Safety

Adverse events were similar, 54.6% with NR and 53.7% with placebo, Medscape reported. Common events included high blood pressure, low folate, falls, nausea and fainting. Serious adverse events were less frequent with NR (8.3%) than with placebo (14.1%), according to the JAMA abstract.

Why the results differ from earlier studies

Cure Parkinson's noted that the results did not match the earlier small studies and said more research was needed to understand why. Possible reasons include:

Eija Pirinen of the Universities of Oulu and Helsinki and Jaan-Olle Andressoo of the University of Helsinki told Medscape that a 2024 mouse study found early improvements in movement with NR did not last with long-term use, and were linked to lower dopamine. "For a chronic disease, a short-term positive result is not enough. We need to know what happens when treatment continues," they said.

Tzoulis told Medscape that substituting another NAD precursor was unlikely to produce a fundamentally different outcome, because these compounds share the same main effect.

Expert reaction

"It's always disappointing to get to the end of a large trial like this and not see any improvement," said Dr Becky Jones, research communications lead at Parkinson's UK. She added that the evidence from the study would help strengthen future research trials, and noted there are five other potential disease-slowing treatments in phase 3.

Dr Simon Stott, director of research at Cure Parkinson's, said the data from clinical trials is essential for moving research forward, and "it all brings us one step closer to finding treatments that do work".

Limits of the evidence

• Participants were assessed while on their usual Parkinson's medicines, without a washout, which makes it harder to separate symptom relief from disease slowing (Medscape).
• Dopamine transporter scans may not detect small changes over one year.
• The trial was run only in Norway.
• Only one dose was tested.

The trial was funded by the Research Council of Norway, the K. G. Jebsen Foundation, the Western Norway Regional Health Authority and KlinBeForsk. ChromaDex, a Niagen Bioscience company, supplied the NR and placebo.

What it means for people with Parkinson's

The researchers do not recommend that people with Parkinson's take NR or other NAD-boosting supplements outside controlled clinical studies, the University of Bergen said. Anyone already taking such a supplement should discuss it with their neurologist or Parkinson's nurse. Supplements can interact with other medicines and are not tightly regulated.

This article explains published research and isn't medical advice. Talk to your own doctor or specialist team before changing any treatment.