The Mamma Mia! star's portrayal of the ex-British Prime Minister has been criticised by some former Tory politicians, with Norman Tebbit writing last week that Thatcher was "never, in [his] experience, the half-hysterical, over-emotional, over-acting woman portrayed by Meryl Streep".
However, the Oscar-winning actress has insisted that the biopic was tackled genuinely.
"I felt that if we did it in the right way, it would be okay," she told BBC News. "There is a feeling that the walls are just more permeable between the present and the past and one intrudes on the other."
Of scenes about Thatcher's dementia, she continued: "It's something that I don't think there should be a stigma about, it's life, it's the truth.
"We've all had that moment where you can't remember why you went upstairs and so it was extrapolating that feeling of disorientation, momentary as it is."
The 62-year-old went on: "I wanted to capture whatever it was that drew people to her or meant people have a special venom for her."
> Director Phyllida Lloyd defends Meryl Streep's Iron Lady performance
Watch Meryl Streep in the trailer for The Iron Lady below: