That's sort of true. But I know people who used to smoke everyday and still graduated highschool with ease. There are people who can function just fine while smoking everyday.

That's why I believe that the people you speak of, the ones wasting their lifes on drugs. I think it's not so much caused by the drugs, but much more their attitude towards life. I believe the excessive use of drugs is more a consequence from their attitude, rather than a cause. I think that even if drugs didnt excist, they would still find other ways to throw away their lifes.