Successive thyroid storms treated with L carnitine and low doses of Methimazole The American Journal of Medicine Thyroid Supplement with L Carnitine for Cats Only Natural Pet L carnitine supplementation for the management of fatigue in patients with hypothyroidism on levothyroxine treatment: a randomized, double blind, placebo controlled trial. Semantic Scholar 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.