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 N Oxide: The Good, the Bad and the Unknown Does L carnitine cause fishy body odor? Surprising Truth and Solutions Tonum Investigating the Association between Low Trimethylamine N Oxide Level TACG Dove Medical Press