Frontiers Association between fatigue, peripheral serotonin, and L carnitine in hypothyroidism and in chronic fatigue syndrome Hypothyroidism: What are its symptoms and how is it treated? Is it safe to take L carnitine with levothyroxine (thyroid medication)? 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. Altered carnitine acylcarnitine profiles in levothyroxine treated congenital hypothyroid patients with fatigue: An LC MS MS based study from Bangladesh PLOS One