Trimethylamine and Trimethylamine N Oxide, a Flavin Containing Monooxygenase 3 (FMO3) Mediated Host Microbiome Metabolic Axis Implicated in Health and Disease Drug Metabolism and Disposition 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 What have we here? A man or a fish? The Lancet L Carnitine Benefits: A Complete Research Based Guide 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.