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 Carnitine Deficiency: What Is It, Causes, Symptoms, and More Osmosis What Is L Carnitine? How Could It Help With Weight Management? Wellness Hub Amazon.com: Nutricost Acetyl L Carnitine 500mg, 180 Capsules Non GMO and Gluten Free (3 Bottles) : Health & Household Comprehensive review of the expanding roles of the carnitine pool in metabolic physiology: beyond fatty acid oxidation Journal of Translational Medicine Springer Nature Link Trimethylaminuria (Fish Odor Syndrome or TMAU)