Thanks for your question, Caroline! Taking supplements sometimes can be confusing when there are many choices offered. Research suggests that people with fibromyalgia take the 100 mg three times a day based on Dr. Cordero's study results. Taking a multi-dose offers all day benefits for energy and antioxidant protection for FM. Those with chronic fatigue (SEID/ME/CFS) may take more, based on their symptoms. If you also have rheumatoid arthritis (RA), CoQ10 will help fight any free radical damage from the inflammatory cycle of RA. Keep in mind that while most supplements have a suggested dose, listen to your body and adjust as necessary. CoQ10 is stored as a fat soluble nutrient so you could take the 400 mg if you are trying to cut back on how many supplements you take a day. Just be sure to take with a meal containing fat for best absorption. Hope that helps!