Carnitine: Genetic Variants Affecting Mitochondrial Energy and Health Stabilizing the enzyme in fish odor syndrome L Carnitine: Benefits, Side Effects, And Dosage, Per Dietitians Compounded Carnitine (L) Injection Empower Pharmacy 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.