The effect of l carnitine supplementation on mortality and clinical outcomes in ventilator dependent critically ill patients with obesity and COVID 19: Protocol for a randomized double blind placebo controlled trial ScienceDirect L Carnitine: Everything You Need to Know 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 Treatments of trimethylaminuria: where we are and where we might be heading ScienceDirect L Carnitine Linus Pauling Institute Oregon State University 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.