From the most recent issue of Classicrockmagazine.com, page 146:

Don’t waste your time doing hard drugs.  The pot’s okay, but he coke and heroin are a complete waste fo time.  It nearly killed me, and I would have loved not to have wasted all that time doing the hard stuff.  Time, it turns out, is the final currency.  To waste it is a sin.  And I wasted a lot of it.  But you can’t do anything but learn and move on.  There’s an argument that says you have to go through a lot to become who you are, but I hate to think I had to go through that to become me.–David Crosby