Excessive use of drugs eventually affect human lives and some people go over board with its usage so if there are harsh punishment for using this drugs then the fear to use it and be caught.
All drugs are dangerous and its not because of the drug itself but the usage, so many of this pain killer drugs are turning people into something else without their addiction to it, some people cant go about their daily lives with it so each and every drug no matter how seriously dangerous or subtle it is, they will eventually cause harm to lives, dont mean to sound biblical but all sins are equal in the presence of God so if excessive use of conedine is treated as cocaine then people who fear punishment will do without it.
Marijuana is 50/50 since it has its advantage and disadvantage.