COQ7-IN-1, a highly potent inhibitor of human coenzyme Q (COQ7), interferes with ubiquinone (UQ) synthesis. COQ7-IN-1 does not disturb physiological cell growth of human normal culture cells. COQ7-IN-1 can be used for the research of the balance between UQ supplementation pathways: de novo UQ synthesis and extracellular UQ uptake.