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 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. I'm a young woman with TMAU (Fishy Odor Syndrome) does anyone have some supplements suggestions for me? Yes I've been to the doctors, specialists and psych, they tell me nothing is wrong, L Carnitine L Tartrate Powder True Protein 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.