The 24-year-old actress told her Twitter followers in June that being an actress "isn't as fun as it may seem."
"If I don't love something anymore I stop doing it. I don't love acting anymore so I've stopped doing it," she tweeted. "I've never written the movies & TV shows I've been a part of I've only acted like the characters the producers or directors wanted me to play ... I know 24 is a young age to retire but you heard it here first. I've retired."
Since getting her break on Nickelodeon's Figure It Out and All That at age 10, Bynes has headlined her own show, The Amanda Show, starred on the WB series What I Like About You, and racked up film credits on What a Girl Wants, She's the Man and Hairspray.
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An e-mail to the star's rep about the latest tweet was not immediately returned.