Lessons in Chemistry Author Talks Changes from Book to Series: 'I'm Not Going to Compare' (Exclusive)

Bonnie Garmus was happy to let go a bit when it came to adapting her book Lessons in Chemistry for TV — but that doesn't mean it was easy.

The author spoke with PEOPLE for this week's issue amid the release of the Apple TV+ series, based on her best-selling 2022 debut novel, starring Brie Larson and Lewis Pullman.

Larson plays protagonist Elizabeth Zott, a cook, mother and accomplished chemist whose goal of being respected in the scientific community is thwarted at every turn in 1950s patriarchal society.

When agreeing to the series, Garmus, 66, recalls to PEOPLE, "I thought, 'Oh my gosh, what if they changed X, Y and Z?' They did change X, Y, and Z. And you know what? I'm still living and breathing. I'm fine."

"As a writer, you want everything to be as you saw it, but you know going in that it can't be that way," she adds. "So it's just smart to say, 'No, let them go,' because you can't demand that they stick with your vision."

Among some of the changes are the pageant storyline in the series' first episode, which was not in the book at all, and the way Elizabeth's beloved dog, Six-Thirty — who is based on Garmus' late dog Friday — is portrayed.

"Six-Thirty is quite different," she explains, noting that the dog "was going to be a mountain to climb," as he's "a hard character to get down."

"So I think that there will be things like that where people go, 'Oh,' or they'll say, 'I can't wait until she says this speech,' and it's not in there," Garmus says of possible reactions from fans of her novel, which was named Barnes & Noble's 2022 Book of the Year.

"But on the other hand," the author continues, "maybe they'll find other things that they enjoy even more" in the series than they do in the book.

"So for me, I almost feel like the book is one thing and the series is something else completely, and I'm not going to compare the two of them," she adds. "And you know what? The author is super biased."

As for having Larson, 34, play Elizabeth, Garmus — who is also a co-executive producer on the show — says she had a Zoom meeting with the actress in which Larson spoke with her about starring and executive producing, which the author calls "a dream come true."

"She was just so normal and so nice. I was really taken with her very direct honesty, and I liked that when I saw that in her," Garmus says. "And I just thought, you can't really go wrong with an Academy Award winner who wants to executive produce and star in your series."

For more from Bonnie Garmus, pick up the latest issue of PEOPLE, on newsstands Friday, or subscribe here.

She also praises the "really good" performances of both Larson and Pullman, 30, the latter of whom plays Elizabeth's fellow chemist and love interest Calvin Evans.

And while she initially wasn't sure about Pullman's physical build for Calvin, who is also an avid rower, Garmus says that "he does such a good job" with the character that it wasn't a concern.

At the end of the day, Garmus tells PEOPLE, she feels "so lucky" and "grateful" that her book has inspired a TV show and admits, "I can't even believe it got made."

"I mean, how is that even possible?" she says. "So yeah, I'm not going to complain about a thing."

Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from juicy celebrity news to compelling human-interest stories.

The first two episodes of Lessons In Chemistry are now available to stream on Apple TV+. Additional episodes will drop Fridays through Nov. 24.