Alex Wolff stars as a boy ultimately possessed with a demon's spirit after killing his sister

Alex Wolff Opens Up About Playing a Character Becoming an Addict in 'Castle in the Ground'
Alex Wolff Opens Up About Playing a Character Becoming an Addict in 'Castle in the Ground'
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Alex Wolff did not come away unscathed from the deeply terrifying Hereditary.

Wolff starred in the 2018 horror as Peter, a teenager whose life unravels after he accidentally kills his sister and ends up possessed by a demon's spirit that haunts his family.

In a new interview, Wolff, 23, says starring in director Ari Aster's film left him with psychological damage, including loss of sleep.

"I'll tell you that movie did about as much damage to me as a movie can do," Wolff told Looper, adding that the experience "really affected me."

The actor shared that he's had a hard time opening up about the lasting effects because he doesn't want to sound ungrateful for starring in the hit film.

"It's very hard because as an actor, you really don't want to sound pretentious or self-serious or like anything is too serious," Wolff said. "Because we have a cushy job in a lot of ways, but this, emotionally, it was one of those tough ones, it was one of those ones that really did some gymnastics on my emotional well-being."

Alex Wolff in Hereditary

Wolff has opened up about the lasting effects of filming tough roles in the past.

The young actor previously starred as Henry in Castle in the Ground, who loses his mom to cancer and then descends into a world of addiction.

Wolff told PEOPLE and Entertainment Weekly at the Toronto International Film Festival that the movie hit close to home after his own dad survived a cancer that was supposed to be fatal.

"I sat next to my parents at the screening, it was definitely weird and heavy to sit next to them," he said. "At the time it was definitely kind of eerie going through it again, a lot of things were similar except my dad survived. My dad had a terminal cancer, he had a full on death sentence. He's like one of the only people to survive it."

"I was definitely hardcore triggered, but I felt super safe and worn into this rough world and I was in a place where I was ready to burn, so to speak," Wolff said of filming the movie and Campbell's death scene. "I just felt very safe. It felt like I was free to go back there, and what was so great about this process, [director/writer Joey Klein] knew my situation and was very sensitive about imposing. He was really open to me bringing up what happened to me and my feelings with it."

Though the experience was hard, Wolff said he's happy to have gone through it and have the chance to work through his feelings in a safe place.

"At the end of the day, you get to make a movie and a lot of people don't have the opportunity to work through things in a healthy way. A lot of people can't afford therapy and things like that. This was a nice, therapeutic thing," he said.

Wolff now stars in Old, which is playing in theaters.