I was looking forward to this role for Blake so I am sad to see her being replaced.

In her first lead role since her Oscar-nominated turn in The Girl With The Dragon Tattoo, Rooney Mara has just committed to starring in Side Effects, the Steven Soderbergh-directed thriller. Mara will replace Blake Lively in a film that also stars Jude Law, Channing Tatum and Catherine Zeta-Jones. Mara plays Emily Hawkins, a sexy but unsettled young woman who is taking serious amounts of prescription drugs to deal with anxiety and depression surrounding the pending release of her husband from prison.

Source: Deadline