Amanda Bynes has spoken out for the first time about how drug addiction ruined her acting career and life.
The child star, now 32, got her big break on Nickelodeon's The Amanda Show before going on to star in films She's the Man and Hairspray.
It was her performance in the former that caused her to become depressed and turn to drugs.
She retired from acting in 2010, filling time with Twitter rants, which left her "ashamed and embarrassed".
"I can't turn back time but if I could, I would. And I'm so sorry to whoever I hurt and whoever I lied about because it truly eats away at me," she told Paper Magazine.
"It makes me feel so horrible and sick to my stomach and sad. Everything I worked my whole life to achieve, I kind of ruined it all through Twitter."
"It's definitely not Twitter's fault - it's my own fault," she adds.
Bynes's drug use started with marijuana at the age of 16, but it was when she started taking Adderall, a medicine used to treat people with ADHD (attention deficit hyperactivity disorder), that her problems began.
"When I was doing [2011 film] Hall Pass, I remember being in the trailer and I used to chew the Adderall tablets because I thought they made me [more] high [that way]," she says.
"I remember chewing on a bunch of them and literally being scatterbrained and not being able to focus on my lines or memorize them for that matter."
She says she remembered "seeing my image on the screen and literally tripping out and thinking my arm looked so fat because it was in the foreground or whatever and I remember rushing off set and thinking, 'Oh my god, I look so bad'."
Bynes pulled out of the film, which was the last project she worked on.
It was from there that her notorious Twitter rants began, in which she criticised fellow celebrities, the media and her own family.
"I had a lot of time on my hands and I would 'wake and bake' and literally be stoned all day long," Bynes admits.
"I got really into my drug usage and it became a really dark, sad world for me." She describes her life back then as one in which she "was just stuck at home, getting high, watching TV and tweeting."
Between 2010 and 2014 she had a number of well-documented run-ins with the police, which eventually lead to her being put under a conservatorship.
This included being sentenced to three years probation after she hit a police car in Los Angeles in 2012.
Bynes also appeared in a New York court in 2013 on allegations that she threw a marijuana bong out the window of her 36th-floor Manhattan apartment.
In August that year she was placed under conservatorship of her parents and put on psychiatric hold for a year after starting a fire on the drive of her home in California.
Her mother was put in charge of the star's financial and legal affairs as a result.
But after that time, she was again arrested for being under the influence in October 2014.
Bynes says she has now been clean for four years, crediting her parents with helping her "get back on track".
She is now a merchandise product development student at the Fashion Institute of Design and Merchandising in Los Angeles and will graduate in November, before embarking on a new degree there in January.
The star says she would eventually like to create her own fashion line one day - but says for now getting back into acting is her first priority.