Hardly drugs: if you exclude cigarettes, he was not a drug taker, and if you read his book, he was a moderate conservative. How bout them apples. I once met Adrian Belew, who guitared for him in the late 70s (listen for his hilarious impression of Bob Dylan on either Joe's Garage or Sheik Yebouti, I forget). Adrian said that he had the personal and musical discipline of a Monk.
I've met Frank many times over the years as well as Ike Willis, Napoleon Murphy Brook, Mike Keneally, and Don Preston, they always had good things to say about Frank. At the last Zappa Plays Zappa show I got Dweezil to sign my RDNZL plate from the MINI!
