Customer reviews for Nutricost L Carnitine Tartrate Supplement Powder (100 Grams) 1 Gram per Serving; 100 Servings 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 Stabilizing the enzyme in fish odor syndrome Fish Odor Carnitine TikTok L carnitine: Science Backed Benefits, Risks, and More 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.