Adjust Text Size:change font sizechange font sizechange font sizechange font sizechange font sizechange font size

Access to the latest research — for scientists and people living with PD alike — in PDF's new scientific journal.

Browse Now

Parkinson's HelpLine


Learn More

Science News

High-Dose Coenzyme Q10 Does Not Slow Parkinsonís Progression

Taking high doses of Coenzyme Q10, a dietary supplement that can be purchased over-the-counter, had no effect on the progression of Parkinson’s disease (PD) symptoms in a large group of people with early-stage disease. The results of this Phase III clinical trial were published in the March 24 online edition of JAMA Neurology.

There is not yet a therapy that is proven to slow the progression of PD.  People in the Parkinson’s community have long held out hope that Coenzyme Q10 (CoQ10) would be proven effective.  Early studies pointed in that direction, with studies at the cellular level showing that CoQ10 addresses processes known to go awry in PD and with studies in cell and animal models showing that CoQ10 protects neurons. A decade ago, one of the first clinical trials of CoQ10 showed that dosages of up to 1200 milligrams daily were safe for people with early stage PD, and also suggested that it helped symptoms.  

For the new study, researchers known as the Parkinson Group QE3 Investigators, led by M. Flint Beal, M.D., at the PDF Research Center at Weill-Cornell Medical College in New York City, tested the effects of higher doses on 600 study participants who had been diagnosed with PD within the previous five years, had mild symptoms, and did not take dopaminergic therapy. On average, participants were 63 years old. One-third of the participants received 1200 mg of CoQ10 daily, one-third received a dose of 2400 mg daily, and one-third took placebo pills for 16 months, or until the participant needed to begin dopamine therapy. Neither medical personnel nor participants knew who received placebo or medication, or at what dose. Every four months, participants were evaluated with the UPDRS, a standard rating scale of PD severity, and to determine whether they needed other treatment.


  • Participants tolerated CoQ10 well.
  • CoQ10 was safe at the dosages tested.
  • Compared to placebo, CoQ10 showed no clinical benefit.
  • Because CoQ10 did not slow disease progression compared to placebo, the study was ended.

What Does It Mean?

Clinical trials serve the purpose of helping to determine if drugs are safe and effective.  While CoQ10 was shown to be safe, this study shows it is not effective in treating Parkinson’s disease. However, even though this study did not reveal this therapy to work, it was a large clinical trial that allowed researchers to perfect how to effectively run a clinical trial – so researchers can feel confident that the study design will not hinder the discovery of the next potential PD therapy.

The study also underscores the need for large-scale, placebo-controlled clinical trials in proving the effectiveness of potential new drugs. For example, in early studies, CoQ10 had all the marks of a successful therapy: researchers understood how it worked at the molecular level; in laboratory and animal studies this understanding was borne out; and in a small trial it was proven safe and seemed to have a small benefit for people with PD. Yet testing CoQ10 in a large number of people with PD provided definitive evidence that it does not slow disease progression. 

That said, this research may not be the end of the road for CoQ10. The study authors note that administering CoQ10 in a different form might have the potential to provide a therapeutic effect. Or, if PD could be diagnosed earlier, before a person has lost many dopamine neurons, CoQ10 might have a detectable neuroprotective effect. These studies remain for the future.

Learn More

Do you have questions about this clinical trial or other medications used to treat Parkinson's disease? Find answers by using PDF's free resources below or by contacting our HelpLine at (800) 457-6676 or, Monday through Friday, from 9:00 AM to 5:00 PM ET.
Learn More about CoQ10 Trial

Reference: The Parkinson Study Group QE3 Investigators et al. (2014) A Randomized Clinical Trial of High-Dosage Coenzyme Q10 in Early Parkinson Disease: No Evidence of Benefit. JAMA Neurol. (ahead of print) DOI: 10.1001/jamaneurol.2014.131

Your gift can help to support research to improve the lives and futures of people touched by Parkinson's. PDF is a 501(c)(3) organization and all gifts are tax deductible.
Donate Now

Source Date: Apr 22 2014