Liquid L Carnitine Core Nutritionals 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. 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 Biotech USA L Carnitine 3000mg with Flavor Orange 20 x 1ml Skroutz.mt Stabilizing the enzyme in fish odor syndrome