Understanding L Carnitine Deficiency and Its Side Effects If you are like a lot of people, you may have never heard of carnitine but this important nutrient is critical for our body's ability to optimally burn fat required for energy. Frontiers Association between fatigue, peripheral serotonin, and L carnitine in hypothyroidism and in chronic fatigue syndrome CARNITINE , any one tried this for chronic fatigue ? I've just found out about this . Carnitine acylcarnitine translocase deficiency: MedlinePlus Genetics