The adverse effects of long term l carnitine supplementation on liver and kidney function in rats L Liu, D M Zhang, M X Wang, C Y Fan, F Zhou, S J Wang, L D Kong, 2015 Does L carnitine cause fishy body odor? Surprising Truth and Solutions Tonum What are the benefits and side effects of L carnitine (Levocarnitine)? Revisiting the Role of Carnitine in Heart Disease Through the Lens of the Gut Microbiota 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 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.