Amanda Seyfried is living with obsessive compulsive disorder (OCD).

Amanda Seyfried on Allure cover

Amanda Seyfried on Allure cover

The 30-year-old actress - who has starred in 'Mean Girls' and 'Ted 2' - has had the mental health condition for years and takes

antidepressant Lexapro to help her control the symptoms.

Speaking in the November issue of Allure magazine, she said: "I've been on it since I was 19, so 11 years. I'm on the lowest dose. I don't see the point of getting off of it. Whether it's placebo or not, I don't want to risk it. And what are you fighting against? Just the stigma of using a tool? A mental illness is a thing that people cast in a different category (from other illnesses), but I don't think it is. It should be taken as seriously as anything else."

The newly engaged beauty - who got betrothed to Thomas Sadoski in September - admits the condition has had a negative impact on her life and at one point she thought she had a brain tumour but it was just her anxiety making her believe that.

She explained: "You don't see the mental illness: It's not a mass; it's not a cyst. But it's there. Why do you need to prove it? If you can treat it, you treat it. I had pretty bad health anxiety that came from the OCD and thought I had a tumour in my brain. I had an MRI, and the neurologist referred me to a psychiatrist. As I get older, the compulsive thoughts and fears have diminished a lot. Knowing that a lot of my fears are not reality-based really helps."

The 'Mamma Mia!' star admits living in the public eye does not help her symptoms and fame can make her OCD worse.

She confessed: "It's funny when insecurity hits you. Sometimes I feel I know the world so well, but then ... it's so debilitating. You're like, 'What am I doing here? No one wants to see me. Why are you taking my picture? It's stupid, it's irrational, and it's not all about me, but I make it about me because I'm insecure."

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