A 22-year-old former addict wrote about rehab, and his famous dad Rob Reiner made it a movie

For the last 30 years, Rob Reiner has been best known for directing movies like "Stand by Me," "The Princess Bride," "When Harry Met Sally," and "A Few Good Men." The titles have brought joy to millions.

But the Reiner household hasn't been all happy. The legendary actor/filmmaker's son, Nick, 22, has been battling drug abuse since his late teens.

Most families would want to keep that part of their lives as hidden from public view as possible. But Reiner admits that, even at the darkest moments of his son's addiction, he thought of making a movie. Yet it was too painful to put pen to page and begin a script.

Interestingly enough, his son came to the same realization as a means to rehabilitate.

While at a rehab center in Los Angeles four years ago, Nick befriended fellow addict Matt Elisofon. The two began writing about their challenges with addiction and the people they met at rehab. Eventually they came up with a script for the movie "Being Charlie" (in theaters Friday), which they asked Rob to direct.

The film had its world premiere at the Toronto International Film Festival last September to a sold-out crowd.

It's a mix of drama and comedy that focuses on an 18-year-old named Charlie (played Nick Robinson of "Jurassic World" fame) as he struggles with addiction to heroin and cocaine. As Charlie jumps in and out of rehab, the aggravation of his actor-turned-politician father (Cary Elwes) grows, and he doesn't know how to help his son.

"It was a real corrective emotional experience," Nick Reiner told Business Insider following the TIFF screening about making the movie.

It took "Being Charlie" four years to get to the screen (in that time Nick has been sober), evolving from a half-hour comedy, then an hour dramedy that was rejected by the TV networks, to finally a feature film.

According to Rob Reiner, what the project lacked in its early development was telling both the father's and son's sides.

"It needed what he has been through but also what we had been through," Rob told Business Insider, referring to himself and his wife, Michele, who was sitting beside him.

Nick and Elisofon were by Rob's side throughout filming. According to Rob, the script was tweaked daily to make the scenes more true to life.

"I relied on him," Rob said of his son. "He's the heart and soul of the film."

One of the biggest adjustments came while shooting the film's ending, in which Charlie and his father finally have a heart-to-heart.

Rob and Nick couldn't find the right tone. After constant rewrites, they finally felt they had something a few days before shooting the scene. It's a gripping moment when both the father and son open up to each other like they never have before.

The Reiners compare getting the ending right to the whole experience making the film.

"We were healing as we were going along," Nick said. "And it all doesn't happen overnight. Certain things we hadn't dealt with for a while but we were able to through this movie. It didn't fix everything, but it really tapped into - "

Nick paused to find the words, then his father, sitting across from Nick, finished for him.

"It forced me to really have to understand what he had been going through for a long time," Rob said.