The Chelsea full-back was amid a string of reports that he had cheated on the Girls Aloud star during their four-year marriage.
Cheryl wrote in her book Cheryl: My Story: "I was still in shock. I wasn't in control of myself at all. I needed medical help.
"We had a videoshoot for our new single coming up and my doctor gave me a vitamin injection in my bum to perk me up, but it didn't work. It was now about two weeks after the initial allegations and, looking back, I was out of my head on tranquillisers."
The 29-year-old divorced the England international in 2010.