Storch and colleagues conducted a multicenter, randomized, double-blind, placebo-controlled, stratified, parallel-group, single-dose trial of coenzyme Q10 (CoQ10) to determine whether nanoparticular CoQ10 is safe and displays symptomatic effects in patients with midstage Parkinson disease (PD) without motor fluctuations. One hundred thirty-one patients were entered into the study. Statistical analysis according to the stratification did not result in significant changes of the primary outcome variable. The frequency and quality of adverse events were similar in both treatment groups. This is the first trial systematically investigating the safety and symptomatic efficacy of high doses of CoQ10 in patients with PD. This study does not support the hypothesis that restoring the impaired energy metabolism of the diseased dopaminergic neurons leads to symptomatic benefits in PD. The study does allow the implementation of future studies with patients with PD to explore the protective effects of CoQ10 at the highest effective dose over a long treatment period.