The 71-year-old guitarist gave up heroin in 1978, cocaine in 2006 and eventually claimed he had "given up everything" in 2010, with his most recent comments suggesting he has since been lured back to smoking cannabis.
However, the musician - who is married to model and actress Patti Hansen, 59 - doesn't dabble in any stronger substances.
Asked if he still drinks alcohol, he told MOJO magazine, "I like to keep my hand in," but insisted, "Other than that, I'm pretty straight."
Writing in his 2010 autobiography 'Life', Keith said he believes the secret to his good health is that he was careful not to overdo things when it came to his drug taking.
He wrote: "I'd never put more in to get a little higher. That's where most f**k up.
"It's the greed involved that never really affected me. People think once they've got this high, if they take some more they're going to get a little higher.
"There's no such thing. Especially with cocaine. Maybe that's a measure of control and I'm rare in that respect."
- Bang! Showbiz
