L Carnitine Capsules Performance Supplements Myvitamins L Carnitine Libido: What the Research Actually Shows L Carnitine Dosage for Erectile Dysfunction: What the Evidence Shows and How to Use It Safely 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.