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 Veterinary Strength Healthy Heart for Dogs & Cats Liquid EVO L Carnitine 3000 HSN Sportseries Does Carnitine Cause Body Odor? Lume Deodorant Is fish smelly? If you have ever caught fresh fish, you know that it doesn't have a particularly strong odor, maybe a hint of ocean water. But when fish are killed, bacteria 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.