Nic Sheff talks about relapses.

8 of 16
Over the years, David says he begged his son to enter a rehabilitation program, but Nic refused.

There was even a time where David says he called hospitals and the morgue every few days to see if Nic had overdosed again or died. "I just had to wait, and I waited," David says. Eventually, Nic agreed to get help.

During one stint in rehab, Nic wrote in his journal, "How the hell did I get here? It doesn't seem that long ago that I was on the water polo team. I was an editor of the school newspaper. ... The kids in my class are in college. This isn't so much sad as it is baffling."

Nic says he never intended to be a drug addict, but once he was, he says he didn't want to stop. Rehab helped Nic recognize that he had a disease, but he says he wasn't convinced at first that he couldn't control his consumption of drugs and alcohol. David says he also struggled with the idea that his firstborn was an addict. "I was very naïve," he says. "I didn't understand addiction."

Over the years, Nic says he has relapsed multiple times and completed five rehabilitation programs. David says it's important for people to remember that relapses are part of the recovery process. "I thought, 'I'll pick him up in 30 days, and thank God, this will be over.' Well, that's not the way addiction works," David says. "Sometimes it takes awhile for them to get it. It's important to understand that because otherwise you feel so defeated. You realize that there's still hope."

When this show first aired in April 2008, Nic said he'd been clean for more than two years. Since then, he's relapsed twice. Today, he says he's clean.