Extreme fatigue can be caused by underlying medical conditions or psychological conditions like depression. Chronic fatigue that lasts over 6 months and reduces daily activity by 50% may be diagnosed as chronic fatigue syndrome. Certain nutritional deficiencies can also cause fatigue. Supplements like iron, magnesium, vitamins B6, B12, fish oil, and CoQ10 may help reduce fatigue symptoms for some people. Dosages vary by individual and supplement, and risks include drug interactions, so one should consult a doctor before taking any supplements for fatigue.