L Carnitine Benefits for Chronic Fatigue Syndrome When to take L carnitine: Dosage, forms, and side effects 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 Compounded Carnitine (L) Injection Empower Pharmacy LEVOCARNITINE INJECTION, USP1 g per 5 mL vial and 4 g per 20 mL vialFOR INTRAVENOUS USE ONLYRx Only