The Your Highness actress told Entertainment Weekly that while she is a big fan of "stoner comedies", she feels it is no longer practical to use drugs in her daily life and has grown out of the habit.
"I love stoner comedies. I smoked weed in college, but I haven't smoked in years," she explained. "I'm too old. I wish I was that cool, but I'm like an old lady now. I'm in bed by 10pm. I can't do that anymore."
She went on to say that while her Your Highness role may have been an unconventional choice, she became excited about the project after sitting down with the film's director David Gordon Green.
"When I sat down with David, he was like, 'The girl's going to be funny here'," she recalled of their first meeting. "To have him be able to think of me in that way was so lucky, because [the role] is a real departure from anything I've done on film."
Your Highness opens in theatres worldwide on April 15.
Portman announced that she and fiancé Benjamin Millipied are expecting their first child together in December 2010. It was recently suggested that the child will be a boy.
Watch the trailer for Your Highness below.