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 Exploring Trimethylaminuria: Genetics and Molecular Mechanisms, Epidemiology, and Emerging Therapeutic Strategies Supplements & Body Odor ConsumerLab.com Trimethylaminuria (Fish Odor Syndrome or TMAU) Treatments of trimethylaminuria: where we are and where we might be heading ScienceDirect