L carnitine treatment in a seriously ill cancer patient with severe hyperthyroidism Adding L Carnitine and Selenium to Methimazole in Graves' Disease: A Prospective Randomized Trial on Thyroid Markers and Quality of Life Carnitine and Thyroid Disease page 1 Life Extension 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.