Olivia Wilde, Jake Johnson, and Ron Livingston were among the celebs buzzing about boozing at the Los Angeles premiere of “Drinking Buddies.”

Wilde, who walked the red carpet on Aug. 15 at ArcLight Hollywood with fiancé and costar Jason Sudeikis (uncredited in a small role), had beer on the brain. She and Johnson had to endure a grueling boot camp that consisted of drinking and brewing local Chicago craft beer.

“We had to know a fair amount so that we could improvise about beer,” she said. “My character works as a PR rep for a beer brewing company so I had to be able to wax poetic about beer.”

Speaking of buzzing, the cast drank real beer while filming the comedy about the blurred lines between friendships and romantic relationships — made even hazier with alcohol. The cast was often tipsy, but Anna Kendrick (who didn’t attend the premiere) was flat-out drank during one scene.

“She didn’t know the beer was real and we were playing a drinking game where she had to drink and she chugged a beer and it’s an IPA with a high alcohol count,” Johnson recalled. “It got on top of her.”

If that wasn’t authentic enough, the film was also entirely improvised. The cast knew the general story arc, but didn’t have set lines to deliver.

“It’s really a process where everybody needs to be in the moment,” director Joe Swanberg said. “They need to be listening to each other and reacting honestly and I need to be paying really close attention because there’s not a script to fall back on. The goal of doing it that way is to keep everybody engaged and create situations that feel fun and natural.”

One of those organic moments included Wilde skinny dipping. Because the actors were essentially writing the script as they went along, they were free to make decisions that determined the direction of the story.

“It wasn’t completely chaotic because Joe had an outline; he knew the basic beats of story that he wanted to hit,” Wilde said. “But everything in between was up for interpretation so we discovered it as we went along. There’s entire scenes that only happened because one of us made a choice to do them.”

Wilde ultimately reveled in the “organized chaos,” which she had initially feared. Livingston experienced that same anxiety when he arrived in Chicago and learned he had to start shooting immediately, two days ahead of schedule.

“So they say, ‘Do you mind coming straight in? And we’re going to shoot the breakup scene,’” Livingston said. “My answer was ‘Sure, but someone needs to tell me who I’m breaking up with and why.’”

While the cast was flustered about their newfound creative freedom, Swanberg was scared about losing his. He was concerned that the film’s bigger budget and bigger crew could compromise his creative control.

“I’m coming out of a micro budget world where I could basically do anything I wanted,” Swanberg said. “In the end, I have to say, having all the extra people and the bigger infrastructure really liberated me to be a director. A lot of jobs, that I sort of by default had taken on in the past, other people were there to do them — people who are better at them than I am.”

Given the uncertainty surrounding an improvised movie, one of the film’s producers, Alicia Van Couvering of Dark Arts, said she was in awe of Swanberg’s clear vision.

“The idea of taking what was so special and small and intimate and exquisite — I think I saw his films as relationship studies — and writing it large and expanding it into something that felt like a lot of people could access it was super exciting and risky,” she said.

She was also impressed by Wilde and Kendrick’s inability to gain weight after consuming so much beer.

“We tried our best to make them fat and ugly, but it didn’t work,” she joked. The cast later bonded over beer again at the star-studded after-party at Umami Burger in Space 15 Twenty.

Wilde, who dined on mini burgers and sipped on canned IPA made by Revolution Brewing — the brewery where they shot the film — was flocked by drinking buddies. She then spent some PDA-filled one-on-one time with Sudeikis, who had flown in from London that day and skipped the “We’re the Millers” Berlin premiere to support his leading lady.

Meanwhile, Johnson spent time with his “New Girl” costar Hannah Simone. Other stars in attendance included Justin Long, Melanie Lynskey, Clea DuVall, Katie Aselton, Kate Flannery, and Alia Shawkat.