L carnitine supplements can cause a fishy odor in the breath, sweat, and urine. This is likely due to the formation of trimethylamine (TMA). TMA is also responsible for the pungent smell of 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. Dietary supplementation of l carnitine ameliorates metabolic syndrome independent of trimethylamine N oxide produced by gut microbes in high fat diet induced obese mice Food & Function (RSC Publishing) JCI l Carnitine in omnivorous diets induces an atherogenic gut microbial pathway in humans Effect of dietary fiber on trimethylamine N oxide production after beef consumption and on gut microbiota: MEATMARK a randomized cross over study European Journal of Clinical Nutrition L Carnitine Side Effects & Safety: A Complete Guide The Science of Good Health