Carnitine: the claims and why it may not work Frontiers Association between fatigue, peripheral serotonin, and L carnitine in hypothyroidism and in chronic fatigue syndrome L carnitine is a naturally occurring amino acid structure that is made in the human brain, liver, and kidneys. L carnitine plays a critical role in energy production, as it converts fat into energy. Supplements and chronic pain: What does the research say? Some studies suggest possible benefits for: Acetyl L Carnitine (energy for cells; studied in diabetic nerve pain) Alpha Lipoic Acid (antioxidant; may ease nerve pain,