The Welsh actress plays Dr. Victoria Siebert in the star-studded thriller, and admits she has always wanted to portray a medical scholar on the big screen.
She tells Wenn, "I'm actually thrilled that Steven cast me as a doctor because I never went to college and I always wanted an 'M.D.' after my name, so I'm really quite flattered.
"And he fulfilled my mother's dream."
She also hopes the film, about a young woman who commits murder while experimenting with prescription drugs, will make people think more carefully about the pills they're given by doctors: "I think culturally we're all victims to a quick fix whether it's texting or if you want a movie you press a button and it's on; we want everything instantaneously.
"With prescription medicine it's the one thing you can take that will make all this go away - 'I'll try it' and if that doesn't work you see a commercial on Tv and try that - 'That seems like a good one'."