Frontiers Association between fatigue, peripheral serotonin, and L carnitine in hypothyroidism and in chronic fatigue syndrome 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 Carnitine: the claims and why it may not work L Carnitine: Benefits, Risks, and Its Role in Fitness and Weight Loss WellnessPulse