Amanda Bynes thinks she "ruined" her career through Twitter. The 'Easy A' actress admitted she is "really ashamed and embarrassed" about a period in her life when she a lot of drugs and posted a number of bizarre and hurtful messages about her family and other celebrities, including some infamously vulgar posts about Drake, and the comments still "eat away" at her. She said: "I'm really ashamed and embarrassed with the things I said. 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. 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." The 32-year-old actress even made the "really foolish" decision to announce her retirement on the microblogging site. Amanda - who has been sober for four years - admitted her substance abuse "messed up" her brain and turned her into a different person.