L Carnitine: Does it help with weight loss? L Carnitine for Dogs: Key Benefits that Every Pet Parent Must Know! Potential Adverse Effects of L Carnitine Marnys L Carnitine A Review of Benefits, Side Effects, and Dosage 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.