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 TMAU: Diet to reduce a fishy odour Dietitian's Life L Carnitine Injection Levocarnitine IV Amazon.com: 5% Nutrition Rich Piana Liquid L Carnitine 3150 Premium 4 Source Blend + GBB, The Super Carnitine (Mandarin Orange) : Health & Household Does L carnitine cause fishy body odor? Surprising Truth and Solutions Tonum 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.