As 'The Exorcist' turns 50, star Linda Blair says it's not actually a horror movie

• Linda Blair is best known for playing demonically possessed Regan MacNeil in "The Exorcist."
• The actor spoke to Business Insider to celebrate the 50th anniversary of William Friedkin's movie.
• Blair says "The Exorcist" isn't a horror movie — it's a religious thriller.

It was the day after Christmas in 1973. Usually this time of year, movie theaters were packed with families wanting to watch something cheery over the holidays. But something peculiar happened this particular year. The big festive theatrical release wasn't a movie fit for all the family — though, indeed, there was a family at the heart of it.

Instead, there were reports of people vomiting, fainting, and even several heart attacks, according to a piece published in The New York Times the following January.

The film was "The Exorcist," director William Friedkin's now-classic tale of a desperate single mother whose 12-year-old daughter is demonically possessed.

Just the mention of the film is likely to conjure images of young Regan MacNeil, played by a then-14-year-old Linda Blair, projectile-vomiting pea soup, crab-walking down the stairs, or her head swiveling 360 degrees with a sickening crunch.

Fifty years later, "The Exorcist" still sets the benchmark for the horror genre — it was the first to be nominated for best picture at the Oscars, and won best adapted screenplay — and that's in large part due to how Blair's performance as the preteen protagonist continues to unsettle audiences. Few movies have been audacious enough to feature a 12-year-old girl stabbing herself in the crotch with a crucifix, and rightly so.

"They'd never seen anything like that, and I was so young. People weren't sure what to make of me," Blair tells Business Insider. "Billy Friedkin tested me with makeup, psychology, and many different things to make sure that I was okay to do the film."

The days Blair spent on set, inhabiting Regan's unsettled mind, were long. "It probably took us three to five days to do one scene, where today you have to finish it in half a day," she says.

When the movie was eventually released, the heavy religious themes in "The Exorcist" sparked debate about whether it was, in fact, sacrilegious. Fifty years on, Blair says that it isn't the horror film that everyone says it is.

"I am proud to be part of it," she says. "It is something that I know has rocked the world in many different ways. I've explained it's a theological thriller. It's not a horror film."

"Bill Blatty intended for it to shock the world, to kind of wake them up," she says, referring to author William Peter Blatty, whose 1971 novel of the same name serves as the movie's source material.

Blair's portrayal of Regan shocked the world, but adding to the hysteria around the movie was the press attention the actor had to cope with upon its release.

"They had conferences where a hundred or more people from the press would show up. And it was quite something to look out to," Blair remembers. "A sea of reporters asking about religion and all the aspects of the movie. And I'm trying to answer them. I'm 15 years old going, 'Well, I think so…'"

The controversy surrounding the movie only served to amplify it; "The Exorcist" grossed $193 million in the US, and was the highest-grossing movie released in 1973. A sequel was all but guaranteed.

Blair reprised her role as Regan in 1977's "Exorcist II: The Heretic," but the film failed to impress both critics — it has a lowly 11% critics' score on Rotten Tomatoes — and fans of the first.

For Blair, the only redeeming quality about the movie was getting to work with the legendary Richard Burton, who played priest Father Lamont. Burton, a veritable Hollywood heartthrob whose relationship with Elizabeth Taylor was the stuff of legend by then, made quite the impression on young Blair, who was by then 17.

"On one side of your mind, you're like, 'Oh, my God, it's Richard Burton!'" she recalls. "And the other side is just holding it: 'Just keep going. Stay in the moment. You're an actor, enjoy the ride.'"

Since "Exorcist II," Blair has had a patchwork of Hollywood credits, including "Roller Boogie" and "Hell Night" in the late 1970s and '80s, and 1990's "Exorcist" spoof, "Repossessed." But for the most part, her passion lies elsewhere.

Blair stepped away from the film industry in the 1990s to dedicate her time to rescuing dogs, largely, she says, because she felt like she needed a greater purpose than just making movies.

"I started rescuing dogs out of shelters in 1997 after my mother had passed. I was really devastated," she recalls. "I felt I had worked for everybody, had just done all these amazing films, but I was looking for my own path."

The actor founded the Linda Blair WorldHeart Foundation in 2003, and has since helped rescue and rehome thousands of dogs.

"I can't go back to regular life as I knew it until changes are made," Blair says, adding that she wants more legal support for animal shelters across the US.

"Anyone that's in animal welfare will tell you it's like PTSD. It's so shocking what we're witnessing," she continues. "It's a full-blown crisis that has to stop. How we treat our animals is how we treat each other."

The foundation has become Blair's life's work; she manages all the day-to-day operations herself, and has 200 dogs living on the property.

It's because of her important work that Blair almost didn't reprise her role as Regan in the recent "Exorcist" reboot, "The Exorcist: Believer." Luckily, the film's producers managed to arrange a small window for Blair to shoot a cameo, which sees Regan reunite with her mother, Chris MacNeil, played by Ellen Burstyn.

Blair also worked closely with director David Gordon Green to ensure that young actors Olivia O'Neill and Lidya Jewett, who play the franchise's latest teen possession victims, Katherine and Angela, were given sufficient support on set.

"I definitely took the girls under my wing and made sure they were taken care of. If they needed a psychologist, if they needed any type of religious mentor, anything," she says. "I was there for them at any time to make sure they knew it's work, it's a film."

It was a full circle moment, says Blair.

"It was like what Billy Friedkin did for me," she says. "Making sure I was fine for the life journey, how to survive, because life is difficult."