I think @Chiro has since made an argument to the contrary. And even if not, I think we could classify opiate usage (at least recreationally) as immoral on the grounds of their highly addictive nature. Drunkenness is a mortal sin because of the diminishing effect it has on the best parts of our nature, our intellect and free will. I think a similar effect is elicited by those who, through the "desensitization to the level of X" as @Chiro has described, come to long desperately for more Y, such that their will ceases in a sense to be as free. This consequence, which many would argue *is* itself necessary, would be sufficient to classify the recreational (uncontrolled) usage of the drug as immoral. A prescription of pain-killers would be different because those negative effects, and the addiction, are controlled by the prescription, as long as this is followed. Recreational use has no inherent controls such as this. I think this is relevant.