Transcript for Amanda Bynes opens up about past drug use, quitting acting and getting sober
Reporter: She was the squeaky clean bubbly star of nickelodeon's "All that." Adios, sucker. Reporter: She shined in blockbusters like "She's the man" and "Hairspray." ??? 'Cause the world keeps spinning round and round ??? ??? and my heart is at the speed of sound ??? and even starred in her own sketch comedy series "The Amanda show." My name's Amanda and welcome to my show! Reporter: But at the height of her career Amanda Bynes endured a sudden public fall from grace. Marked by erratic behavior and bizarre outbursts on social media. Now after several years out of the spotlight the 32-year-old former child star is opening up to "Paper" magazine revealing in the latest issue the truth behind those dark years of what she says was drug abuse. Saying, "It was like an alien had literally invaded my body." Her drug-fueled descent from the top, a storyline so familiar in young Hollywood. Bynes says she began using marijuana recreationally at age 16, then progressed to Molly, ecstasy, even experimenting with cocaine use. When you talk about recreational use of marijuana in the adolescent age group, we know that their brain is very vulnerable. Exposure to any illicit substance can have very serious consequences both short term and long term. Reporter: But her substance of choice became adderall, an amphetamine often used to treat attention deficit hyperactivity disorder. ??? Now I've tasted chocolate and I'm never going back ??? Reporter: Bynes says she learned about adderall when she was starring in "Hairspray" her abuse of the drug son tense that she says she would chew the pills, saying "Because she thought they made her more high that way." The recreational use or abuse of adderall or any other amphetamine it can cause insomnia, anxiety, anorexia, weight loss, rapid heart rate, high blood pressure, sweating, agitation. The list goes on and on and on. She really attributes some of what happened and changes in her behavior and personality to the drug usage as it escalated and became, you know, a much more serious issue. Hey. What's up? I'm Sebastian. Reporter: After seeing herself in the romantic comedy "She's the man," a role in which she plays a teenage girl pretending to be a boy, she says, "I went into a deep depression for four to six months because I didn't like how I looked when I was a boy." I'm not the one you have to answer to for your depraved behavior. There's a higher power that will judge you for your indecency. Tom Cruise. Reporter: And after her work in "Easy a" the actress telling the magazine, "I saw it and I was convinced that I should never be on camera again and I officially retired on Twitter." But says she regretted it, saying "It was really foolish and I see that now. I was young and stupid." She then went into a self-imposed exile from Hollywood and says she fell into a dark hole. She was really open and raw about how that time was not a happy period and was a very dark sad place for her. Reporter: Her downward spiral starting in 2012, making headlines for all the wrong reasons. A series of driving violations, disturbing tweets, even a hospitalization under a psychiatric hold. After starting a fire in a neighbor's driveway an eyewitness describing the unusual scene. I saw this girl laying down right here with her left pant leg on fire. When I look at her, that's Amanda Bynes. Reporter: That incident coming on the heels of another out-of-control episode involving allegations she tossed a marijuana bong out of her 36th floor Manhattan apartment right in front of police officers. She was arrested. Her now infamous mugshot exploding on social media. She appeared at court disheveled. Are you planning on staying? Yes. Reporter: At one point wearing a blight blue wig. Why do you think child stars often struggle with addiction? When you remove a child from the Normal course of their social and psychological development, it's not too surprising that there can be negative consequences. Reporter: Bynes says she has now been sober for almost four years and is ready to get back into acting, telling "Paper" magazine she's not afraid of the future saying, "I've been through the worst and came out the other end and survived it. It's only up from here." This is sort of her wanting to tell her story, kind of close a chapter that was difficult, move on and start the next phase of her life and career. Reporter: How important is it for celebrities to publicly es do have a massive platform that can be very powerful in a positive way. But at times where they're sharing their own personal crisis their primary concern should be themselves. Reporter: For "Nightline" I'm will reeve in New York.
This transcript has been automatically generated and may not be 100% accurate.