The 71-year-old, who is bandmates with the actor in rock group the Hollywood Vampires – alongside Aerosmith's Joe Perry and guitarist Tommy Henriksen – revealed Depp was venting his frustrations and grievances in new songs.
And the legendary rocker was quick to defend his friend, saying despite recent reports in the media, the 55-year-old is in a great place.
"I've never seen him look better in my life. I've never seen him happier. I've never heard him play better, and the way the press would have it is he's a total destruction and ready to die. Totally not true," Cooper told Billboard.
Talking about the band, he continued: "It's really interesting because it's not your normal hard rock. It goes places I wouldn't normally go, and that's kind of what I like about it."
He further explained that Depp's songs focus on his feelings over recent abuse charges by ex-wife Heard, as well as rumours about health and addiction issues.
"I'm spewing his venom on this album, which is kind of good," Cooper said, adding that "all the stuff you heard last year about Johnny, 99 percent was just bull".
Earlier this month, Depp filed a defamation suit against his "Aquaman" star ex, claiming statements she made about his allegedly volatile behaviour following their separation in 2016 were part of an "elaborate hoax to generate positive publicity".
Heard has denied the allegations, and her attorney called the lawsuit "frivolous".