L Carnitine Injection (Intramuscular): How It Works & What to Expect Mesotherapy Cocktails, Exosomes Regenerative Skin Boosters Injectable L Carnitine for Slimming: Does It Really Work? National Medical Resources Inc L Carnitine Linus Pauling Institute Oregon State University 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