L Carnitine is Underrated. New Meta Review Reminds Us Why. The effects of pharmacologically decreased availability of L carnitine Download Scientific Diagram Does L carnitine produce a clinically meaningful effect within four hours? 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 Frontiers Association between fatigue, peripheral serotonin, and L carnitine in hypothyroidism and in chronic fatigue syndrome