Carnitine Deficiency: What Is It, Causes, Symptoms, and More Osmosis L Carnitine injection is recommended at 1 ampule every 2 3 days for best results. The L Carnitine is taken intravenously either by normal injection or using a butterfly needle. After taking this L Carnitine, you 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. Customer reviews for Nutricost L Carnitine Tartrate Supplement Powder (100 Grams) 1 Gram per Serving; 100 Servings Walmart.com