What's the Difference Between CLA and Carnitine? 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: Benefits, Side Effects, And Dosage, Per Dietitians Breakthrough in studying the enzyme that ultimately produces fish odor syndrome EurekAlert! L Carnitine in the Treatment of Psychiatric and Neurological Manifestations: A Systematic Review