If you're using injectable L Carnitine, a 27 gauge, half inch needle is ideal. Anything larger can cause the serum to get stuck. For larger doses, using luer locks can make the process Jay L CARNITINE INJECTION L Carnitine 500mg mL 10mL AMP Research INJECTABLE L CARNITINE MY EXPERIENCE I've used Injectable L Carnitine for over two years (on and off), and here's what I've found: It's not just another fat burner; it's a mitochondrial transport tool