The Confessions of a Shopaholic star plays a cocaine user hooked on partying in her upcoming film Bachelorette, and Fisher admits she was forced to heavily research the role since she never had any experience with drugs.
But the 36 year old's concerns about taking on the part came as a surprise to her pals, who assumed the busy mother of two was relying on illegal stimulants to get her through the day.
Fisher tells Eonline.com, "It's hilarious for me because I've never done coke. When I got the job, I was like, 'How am I going to wing this? I don't have any experience.'
"I asked a few friends what it's like being on coke and they said, 'We thought you were always on coke!' It turns out... because I speak so quickly, people always thought I was doing it! I've never even seen it."