Kelly Osbourne first consumed drugs at the age of 13.
In her new book, Fierce, Kelly has revealed how her first experiences with prescription drugs led to a downward spiral that saw her in rehab four times in six years.
"I had my tonsils out. I was prescribed liquid Vicodin, a strong opiate like heroin, only available in America," the Sun quoted her as saying.
"When I swallowed that tiny dose I felt relaxed and contented. I thought, "I like the feeling this drug gives me". The prescription ran out, and that was the end of that.
"But, three years later, aged 16, I was at Hollywood club Las Palmas when an older guy I'd never seen before said, "Hey, want one of these?". She had a prescription bottle of pills that looked like Vicodin. I took a small white pill and swallowed it. "
"I quickly felt I could talk to anyone. I was relaxed, happy and a bit tingly. It was the same feeling as when I had my tonsils out and I thought, "I've found my magic remedy". The next morning, I called the guy and bought two or three pills for about 20 dollars," she added.
The singer, who is the daughter of rock legend Ozzy Osbourne, spoke about her rehabilitation experience too.
She added: "They checked me into the psychiatric ward at the UCLA Medical Institution in LA, where years later Britney Spears would be sectioned.
"I was so frightened - it was full of crazy people. As I curled up in a tight ball, the air was filled with ear-piercing screams. I didn't leave my room for five days. It's one of the scariest things I have ever done, but also one of the best."