Depends how you are taking it. Heroin is particularly addictive for two reasons: First when you IV something you get the whole dose really fast, that fast huge rush will result in stronger cravings from then on. The other reason is that the chemical structure of heroin makes it very easy to cross into the brain. Opium is morphine and codeine, neither get into the brain as fast as heroin. If you're smoking it you'd get a fast buzz almost as fast as you would IV'ing heroin but I'm not sure if it would be as strong. If you're swallowing it then it has to go through stomach, intestines, liver then bloodstream then into the brain. All this takes time, so you don't get the avalanche of a fast effect like you would IV'ing heroin.