L Carnitine: Benefits, Uses, and Side Effects Lifespan Research Institute Most people talk about carnitine like it is one supplement. It is not. Acetyl L carnitine and L carnitine L tartrate do different jobs, and picking the wrong one for the wrong goal is where people L Carnitine Side Effects & Safety: A Complete Guide The Science of Good Health Does L carnitine cause erectile dysfunction? 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.