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 Frontiers The role of trimethylamine N oxide in disease pathogenesis and the therapeutic potential of traditional Chinese medicine Cardiovascular risk of dietary trimethylamine oxide precursors and the therapeutic potential of resveratrol and its derivatives Hou 2024 FEBS Open Bio Wiley Online Library Treatments of trimethylaminuria: where we are and where we might be heading ScienceDirect Did You Know? Some people report a fishy smell after supplementing with L carnitine. This happens because certain gut bacteria convert carnitine to trimethylamine, a malodorous compound found in rotting fish.