The 28-year-old said she was motivated to break out of her "little bubble of self-medicating" and lose 50lbs after experiencing suicidal thoughts.
"If you look at pictures of me [before the weight loss] - how unhappy I really was," she told ITV1's Daybreak and Lorraine today (January 7). "You can see it in my eyes.
"I didn't want to change because I had cocooned myself into this little bubble of self-medicating and numbing myself. And I can't lie, I thought, 'If I just take a couple more of these I won't wake up tomorrow morning, it'll all be done, who cares?'
"I woke up the next day and was like, 'You actually thought that about yourself - you need to sort that', and I told my mum and that day I was in rehab... I didn't think I'd make it to 28."
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Copyright: Rex Features Beretta/Sims/Rex FeaturesOsbourne went on to describe her route to good health as an "insane... great journey".
"A lot of it has sucked but I'm telling you hard work has paid off," she said. "I had to learn to love myself and once I kind of got there - because every woman has a problem with something with themselves - I started to realise I should look after myself a little bit better.
"One pound started to drop and then five pounds and I was like, 'Wow this is addictive'. I never thought I'd be the girl who gets up every day and goes to the gym."
Watch Kelly Osbourne chat to Digital Spy below: