In “Killer Joe,” Matthew McConaughey, left, plays the titular assassin, while Gina Gershon, right, is a sharp-tongued Texan with a secret.

Gina Gershon specializes in adult films. Not that kind! Well, not quite that kind. Granted, two of her most iconic roles were as bisexual Vegas dancer Cristal Conners in director Paul Verhoeven’s 1995 campy stripper soap “Showgirls” and as lesbian crook Corky in Andy and Lana Wachowski’s 1996 hard-boiled con flick “Bound.”

Now, Gershon is adding to that list with “Killer Joe,” William Friedkin’s new, NC-17-rated film about murder, drugs and money based on Tracy Letts’ 1993 stage play by the same name. Gershon plays Sharla, a sharp-tongued Texan with a secret and a special affinity for fried chicken. (Also in development: “Harem,” a Starz miniseries she can’t say much about yet, and a memoir called “In Search of Cleo: How I Found My Pussy and Lost My Mind.”)

You were offered this role years ago in the stage version. Why did you turn it down then?
It was sent to me, and as much as I loved it and thought, “Wow, this guy really can write,” psychologically and emotionally, I didn’t want to go there eight times a week for however long. It was so incredible, but it was so intense. So, when it came around again, I started reading it and I was like, “Oh my God! It’s that play!” This time I only had to do it once.

“Showgirls” also got an NC-17 rating. What do you think of the ratings system in general?
I think the whole system is quite arbitrary. But between this and “Showgirls” both being NC-17, this definitely deserves the NC-17 rating more. I really don’t understand why “Showgirls” was NC-17. This [movie] is violent and intense and visceral. Not every 11-year-old should see this movie. I mean, when I was 11, I probably would have been into it.

In 2007, you wrote a young adult book called “Camp Creepy Time” with your brother. But “In Search of Cleo” — which has a rather racy subtitle but is actually about losing your cat — is your first memoir. How did that come about?
A few years ago, I made an album and played it at this place called the Box. The story of when my cat went missing and what I went through to find him was thematically the same as my music: It’s all about what people go through to find true love. I ended up calling the album “In Search of Cleo” … [but] the album actually has nothing to do with my cat! Then, one thing led to another and I got a book deal.