Cara Delevingne's childhood was ''pretty sad''.

The 22-year-old model-and-actress struggled to bond with her mother Pandora, who was addicted to heroin, and then battled depression as a teenager, but eventually found hope through acting.

She said: ''[My childhood was] pretty sad. My mother battled a heroin addiction for years and is now writing her memoir.

''As a child I suffered a lot because I wasn't able to spend much time with her and then at 15 this terrible wave of depression hit me.

''School was a nightmare for me and life felt awful. That's when I discovered that acting was my only way to feel alive.''

Cara - who is dating musician St. Vincent - always tries to be herself and thinks it is a ''waste of time'' to be guarded in public.

She told Britain's OK! magazine: ''I find that always watching what you see in public is a huge waste of time and really horrible way to live because it's so restrictive.

''I know people who are very preoccupied with what they say and do, and try to say what the public wants to hear. I can't live that way.

''The only real limit I have is what I say about my private life.

''I know something I might say because I'm trying to be funny or because I'm tired or in a bad mood might get me into trouble and then people might feel entitled to judge you.

''I still think though, it's easier for me to be myself and be willing to say I am who I am.''