L Carnitine for Weight Loss: How It Works, Dosage & Best Supplement Zeelab Pharmacy When to take L carnitine: Dosage, forms, and side effects Carnitine: the claims and why it may not work L Carnitine: Benefits, Side Effects, And Dosage, Per Dietitians Carnitine: Requirements, food sources, benefits, and risks 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.