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 IAMS PROACTIVE HEALTH Adult Healthy Dry Cat Food with Chicken, 16 Pounds Pet Supplies Plus L Carnitine Benefits for Male Erectile Dysfunction iSatori Liquid L Carnitine LS3 3000 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.