The actress said that she can relate to the protagonist of the erotic novel by EL James, which recently became one of the fastest-selling books of all time.
"After hearing so much about it from friends and colleagues, I gave in and bought a copy," she wrote in The People.
"And boy am I pleased. I was gripped from the beginning and could relate to Anastasia's journey."
Cassidy explained that the novel has helped her relationship with boyfriend Adam Cottrell, who she began dating again in February.
"Mr Grey and Anastasia's steamy antics are certainly an aphrodisiac. I feel like a different woman. Now when I think of sex, it isn't a chore that I need to fit in, rush or put off."
She added: "I haven't stopped thinking about it. Poor Adam!"
Lucy Hale and Kristen Stewart are among the actresses that have been linked with the leading role in an upcoming movie version.
A culture expert recently predicted that the book will spark a rise in pregnancies in 2012 and 2013.