Coenzyme Q-10, or CoQ10, is a compound that can be made by the body or consumed through food and supplements. It is an important antioxidant and an essential component of the heart’s energy-producing system. The primary function of CoQ-10 is to assist in cellular energy production. Factors such as health status and age may affect the body’s levels of CoQ-10. You can find a CoQ10 supplement at GNC as a standalone ingredient in pills or in products with other ingredients.