Nutricost L Carnitine Tartrate Powder, 100g, 1g per serving Walmart.com 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: Does it help with weight loss? Force Factor L Carnitine Liquid, Berry, 16 fl oz (473 ml) 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.