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Bynes has struggled over the years with mental health and addiction. In an Instagram post earlier this month, she marked 14 months of sobriety.
"Celebrating being sober a year and two months!" she captioned a photo of herself posing next to a man.
Her attorney, David Esquibias, said Wednesday that her decision to seek treatment was related to her mental health troubles, saying reports that she was "suffering from drug or alcohol addiction issues are completely false."
“We ask for privacy during this time, and for any speculation about her personal life from the public and the media to cease so Amanda can focus on getting better," he said.
In 2014, the "She's the Man" star announced on Twitter that she had been diagnosed with bipolar affective disorder and manic depression. Before revealing her diagnosis, Bynes had posted numerous tweets lashing out at her family members and other celebrities.
"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 said. "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."
Minyvonne Burke is a breaking news reporter for NBC News.