Carnitine Molecule of the Month September 2003 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. PDF) [L carnitine treatment and fish odor syndrome: an unwaited adverse effect]. Gamma Butyrobetaine an overview ScienceDirect Topics 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