L Carnitine: Benefits, Side Effects, And Dosage, Per Dietitians L Carnitine vs L Arginine: Understanding Their Differences and Benefit Fitness Health L Carnitine Tartrate Amino Acid 1,500 mg Benevolent Nourishment Liquid L Carnitine 3000 Nutrex Amino Acids 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.