Harding entered a rehab centre in Capetown, South Africa, in October last year, citing alcohol abuse and depression.
But the troubled blonde has now revealed that she was also addicted to Zopiclone tablets.
Of her four-year addiction to the pills, Harding told The Sun she was “out of control” and is now “just glad I survived”.
The 30-year-old said she turned to booze to help cope with her split from her DJ fiance Tom Crane in September.
More recently, Harding has made headlines for her stormy relationship with new love Theo Van Dries, who she met in rehab as he battled cocaine addiction.
The pair had been dating for three months when a fight broke out in their hotel room on New Year’s Day. Harding has filed an official complaint against Van Dries to police, claiming that he bit her and repeatedly smashed her head against the floor.
Speaking to the red top about her time in rehab, Harding said: “Rehab was a depressing place to be with a lot of troubled people. I came off Zopiclone. I started taking them four years ago and coming off them was horrible.
“It took three weeks in rehab to start sleeping normally again.”
But following her fight with Theo, the singer admitted: “This has just messed me up again, because I’m sleeping terrible hours again. My smoking has also got a lot worse.”
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