L Carnitine: Benefits, Uses, and Side Effects Lifespan Research Institute L Carnitine: What it's used for, benefits and how to take it correctly Justloading Carnitine Deficiency: What Is It, Causes, Symptoms, and More Osmosis Carnitine: Genetic Variants Affecting Mitochondrial Energy and Health Did You Know? Some people report a fishy smell after supplementing with L carnitine. This happens because certain gut bacteria convert carnitine to trimethylamine, a malodorous compound found in rotting fish.