Does L carnitine cause fishy body odor? Surprising Truth and Solutions Tonum L Carnitine: What it's used for, benefits and how to take it correctly Justloading Supplements & Body Odor ConsumerLab.com PDF) [L carnitine treatment and fish odor syndrome: an unwaited adverse effect]. 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