Is it safe to take L carnitine with levothyroxine (thyroid medication)? Acetyl l carnitine: Health Benefits, Side Effects, Uses, Dose & Precautions L carnitine supplementation for the management of fatigue in patients with hypothyroidism on levothyroxine treatment: a randomized, double blind, placebo controlled trial. Semantic Scholar This one is for my gym crowd, and those regularly using protein powders and supplements for sports performance or weight loss Do any of your supplements contain Acetyl L Carnitine? If you If you are like a lot of people, you may have never heard of carnitine but this important nutrient is critical for our body's ability to optimally burn fat required for energy.