Wondering what I should do..

I have a really good friend, but this friend has circum to speed and coke. Its one of the more worse drugs out there. As a friend I tried to help, offering alternatives to this persons drug abuse. I have no idea to what extent this person is taking the drug. But I know they are wasting a lot of money just to obtain the drug. I tried to ask why this person was doing it? and how it not only effects him/her but everyone around him/her. This person doesn't seem to understand. This person lashed out at me just because ''I didn't respect his/her choice'' Ultimately yeah it is this person choice to ruin their life. But as a worried friend I tried to step in to save him/her. Wondering what I should do. To save our friendship, and to save my friend.