What Is Acetyl L Carnitine Good For? Uses & Benefits Early research into L carnitine was often cited as underwhelming, showing negligible changes in muscle carnitine content and fat loss outcomes. However, these findings may have been limited by a short study window L Carnitine Dosage for Erectile Dysfunction: What the Evidence Shows and How to Use It Safely L Carnitine Libido: What the Research Actually Shows 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.