Mirren, 69, said it is tough to play her in the play that has small changes from its previous British outings, reported the New York Post.
"Talking right now I'm even having paranoia in terms of saving my voice. Doing theater you depend on it, and I'm onstage nonstop two hours.
"We've made some subtle changes from the British version. Small trims and adjustments. Nothing spectacular. There's a change at the end of Act 1. But we haven't made many concessions," she said.
"Oddly, despite common language, married to an American all these years I'm aware of subtle differences between our countries. The other day I said something, and my husband, Taylor, said, 'What does that mean?' So, a British play about British people, there are a few references Americans mightn't get.
"Doing previews here we can see that, but it's all verbal, light, not heavy, and a universal wit is employed. People understand one another's nature. Even if you didn't know Prime Minister Gordon Brown, what's threaded through is history," she added.