Carnitine: the claims and why it may not work Injectable L Carnitine > Oral L Carnitine BUT do you REALLY need it?, , I dont think so., , L Carnitine is a medicine often prescribed by doctors to patients with heart issues., , In theory, it Acetyl L carnitine in chronic pain: A narrative review ScienceDirect L carnitine is effective for both fat loss and athletic performance. However, oral L carnitine has lower bioavailability and can be harmful at high doses, so it should be avoided. , Even cardiologists