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 Fluoromethylcarnitine, a novel inhibitor of trimethylamine levels in trimethylaminuria and trimethylamine N oxide related disorders ScienceDirect The effect of egg yolk trimethylamine (TMA) concentration on fishy odor Download Scientific Diagram 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.