L Carnitine. Boost Weight Loss & Improve Heart Health Is L Carnitine Safe? Watch FIRST BEFORE Taking L Carnitine Supplements Frontiers Association between fatigue, peripheral serotonin, and L carnitine in hypothyroidism and in chronic fatigue syndrome Dietary supplements: the bad and the ugly > Dyess Air Force Base > Article Display 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