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. What Is L Carnitine? How Could It Help With Weight Management? Wellness Hub L Carnitine Side Effects & Safety: A Complete Guide The Science of Good Health 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.