Asa Somers started with “Next to Normal” when it was next to nothing. A musical about one woman’s mental illness and its effect on her family, “Next to Normal” opened off-Broadway in 2008 to mixed reviews. At the time, Somers was playing the doctor.

He knew the show had its share of problems. There were “warring elements,” both structurally and tonally, that weakened its impact. Big production numbers threatened to upstage the storytelling. Somers thought his role needed a lot of work. But there was potential.

The creators then made the surprising decision to move the show out of town to the Arena Stage in Washington, D.C. Somers wasn’t able to go with them, so his role was recast. But it was during this time that the show’s potential was finally realized. Away from prying eyes, the creators were able to tinker with the material. They cut songs, toned down splashier elements and fine-tuned many of the parts.

When “Next to Normal” opened on Broadway in 2009, critics piled on the praise. The show went on to win three Tony Awards and the 2010 Pulitzer Prize for Drama — the first musical to do so since “Rent” in 1996.

Somers has since returned to “Next to Normal,” which kicks off its national tour at the Ahmanson today with five nights of preview performances before officially opening Nov. 28. He is still amazed by its transformation.

“They got it right,” he said. Compared to the original, only about 20 percent of the material is different, Somers said, “but it has completely, completely renovated the entire show, from soup to nuts.”

Somers thinks of musicals like Hollywood films: There are the summer blockbusters and the indie classics. “Next to Normal” sits squarely in the latter category.

“We are like the ‘Juno’ of Broadway musicals,” he said, laughing.

Unlike most mainstream musicals, “Next to Normal” takes on weighty subjects like mental illness and personal sacrifice. Musicals that try to get serious often flop, but “Next to Normal” struck a chord.

“The odds are always stacked against a new show, especially any new show that tries to break some boundaries,” Somers said. “Change is difficult.”

But the creators were able to “fashion a work of supreme delicacy and sensitivity,” Somers said. Summing up the musical in one word, Somers said it was “life-affirming.”

When Somers returned to the cast, he was the standby for both the doctor and Dan, the husband of the bipolar Diana. When he would go on as Dan, the performances would go particularly well. One thing led to another, and now Somers is playing Dan on the tour. He calls it “the role of a lifetime.”

“You get to feel so very much in this part,” he said. “He’s a caretaker, he’s a voice of reason, but he’s also deeply flawed and not even aware of it.”

Playing Diana on the tour is the woman who created the role, the Tony Award-winning Alice Ripley. Ripley has been widely hailed for her emotionally complex portrayal of a woman in crisis. 

“Working with Alice is fantastic,” Somers said. “She’s a dream come true in terms of an acting partner. She’s so giving, so open to whatever it is I throw out there.”

The musical — which includes nearly 40 songs — delves into the unknowns of the human brain, Somers said.

“We never can crawl into the mind of our neighbor or our loved one and understand exactly what they’re feeling,” he said. “We need to be open-minded and sensitive about that.”

According to Somers, musicals can deal with these nuanced, complicated issues as well as any form of drama. They just haven’t — until now.

“In some ways, ‘Next to Normal’ is pointing the way to the future,” he said.

Reach Senior Arts Editor Jason Kehe here.