Robbie Williams injects himself with hormones that boost his sex drive after he was told he had "the testosterone of a 100-year-old man".
The Angels star, who appeared in a live concert with Take That for the first time in 15 years last week, revealed he was diagnosed after visiting a doctor in Los Angeles in a bid to be prescribed Human Growth Hormone (HGH).
He told Esquire Magazine: "To cut a long story short I went to get some HGH. It's what all the old fellas are on out there in LA that's making them look 40 instead of 60.
"It's improving their health, their memory, their hair, skin.
"Could give you cancer. I weighed that up. Thought I'd have it anyway. Went to see a Hollywood doctor. Had my blood tests. Went back. He said, 'You don't need HGH. You've got the testosterone of a 100-year-old man.'
"And then everything made sense. It was kind of an epiphany that day."
Robbie, who married actress Ayda Field last year, said marriage was "made-up bull" but said he did not want to "break Ayda's heart" by cheating on her.
The Stoke-on-Trent-born singer has had a well-publicised battle with drink and drugs during his career.