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 Trimethylamine Oxide an overview ScienceDirect Topics Breakthrough in studying the enzyme that ultimately produces fish odor syndrome EurekAlert! Trimethylaminuria: Definition, symptoms, and more Acetyl L Carnitine: Benefits, Forms, Dosing, and Side Effects Dr Brad Stanfield