Amazon.com: 5% Nutrition Rich Piana Liquid L Carnitine 3150 Premium 4 Source Blend + GBB, The Super Carnitine (Mandarin Orange) : Health & Household What does the smell of your urine tell you?? Carnitine Deficiency: What Is It, Causes, Symptoms, and More Osmosis 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. Urine normally has a slight smell, but some unusual and strong smells may be a sign that something's wrong.