Amazon.com: 5% Nutrition Rich Piana Liquid L Carnitine 3150 Premium 4 Source Blend + GBB, The Super Carnitine (Mandarin Orange) : Health & Household L Carnitine: Benefits, side effects, and dosage Trimethylaminuria (Fish Odor Syndrome or TMAU) 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 Urine smells like fish: Causes and treatment Urine normally has a slight smell, but some unusual and strong smells may be a sign that something's wrong.