Help My brother is becoming a drug addict?

Ok it first started when I saw my brother smoking pot when I was in 7th grade and he was in 10th. At first I was scared and didn't tell anyone but then I grew and realized a lot of people smoke pot and in moderation its not awful just not good for you. (don't worry he has set an example that I will never touch drugs in my life) Through High school he had a 4.0Gpa with several honers and AP and an 32 act. He decided to attend Alabama and his grades have been slumping at first he had like a 3.8 the 2nd year he just got back a 2.7. What really scared me though is when I saw him (are rooms connect) Snorting white powder through a 10 dollar bill that he stole from me. I guess it was cocaine... Anyway my parents are beyond belief that he got a 2.7. Also he lies to my parents about college. For example he lies that he shows up to class etc... And he is just not the same anymore he has become almost Fake. Even my sister doesn't like him anymore (used to be favorite) As she says he as so different and fake. My parents caught him smoking weed once and were beyond mad and told him never to smoke in the house again or they would not pay for his college. I want to help my brother but don't know what to do. I feel like hes going to grow up like my uncle who is completely messed up from drugs and got a felony for it that screwed up his entire life. I know my brother also does limited amounts of other drugs like acids, heavy drinker at college but only seen him do Cocaine and weed at the house. He also drives while doing drugs to. As a brother should I confront him or tell my parents (i'm in 9th grade)

Thanks