The Coronation Street actress, who has signed a new contract with the ITV soap for at least another year, told The Mirror that she struggled with both anorexia and bulimia in the early days of her career.
The Stella Price star said that the situation came to a head when casters at an audition told her agent they suspected she was a heroin addict.
She explained: "I went to audition for a fashion commercial and they said they didn't think I was quite right for it because I wasn't 'upmarket' enough.
"Later that day my agent called to see if I was okay and told me that actually I had looked so awful the casters had thought I was a heroin addict and wanted to know if I was on drugs.
"That was the wake-up call I needed."
Before securing her breakthrough role as Cindy Beale in EastEnders, Collins said that she would starve herself for weeks and drink alcohol rather than eat.
"It was a running joke with friends that I would order a salad without the oil and then drink copious amounts of alcohol like them," she said.
"That was just what I did because I thought it had fewer calories than food.
"Then as I got worse I was drinking instead of eating so I could still go out and have a good time. I went for weeks without really eating any food.
"I'd starve all day then come home late and binge on anything I could get my hands on.
"I raided the fridge and cupboards then stuck my fingers down my throat to feel empty again. Soon I was doing it after every meal, it was so addictive."
The 50-year-old added: "My arms and legs were scrawny. I had the body of a child, but when I looked in the mirror I still wanted to lose more.
"My life felt out of control and I felt if I could control my body I could control my life. In my head skinny equalled successful and I thought the only way I could be a successful actress was to be a skinny woman."
Digital Spy Soap Scoop video - Amie Parker-Williams previews a big week ahead for Coronation Street, EastEnders, Emmerdale and Hollyoaks.