Heroin's two acetyl groups distinguish it from morphine, and are responsible for making it more potent than morphine. Why? Question 5 options: the acetyl groups allow heroin to cross the blood/brain barrier more easily the acetyl groups make heroin stick to the µ opioid receptor for a longer period of time the bigger molecule means you don't need as much of it we have no idea why heroin is more potent than morphine