Propofol is formulated as a lipid emulsion which causes pain during injection that can be decreased by using a large vein, avoiding veins in the dorsum of the hand, prior injection of lidocaine or by mixing lidocaine with propofol prior to injection (2 mL of 1% lidocaine in 18 mL propofol). prior injection of opioid Thicker vein decreases pain on injection caused by propofol.