L Carnitine: Does it help with weight loss? 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 L Carnitine: Everything You Need to Know 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. Liquid L Carnitine Citrus L Carnitine for Dogs: Key Benefits that Every Pet Parent Must Know!