Many Hollywood celebs struggle with substance abuse, but there are some child stars that have admitted they got mixed up with drugs and alcohol before they could see R-rated movies. Here are some of the most memorable stars who became addicts while they were still kids:

1. Mackenzie Philips


(AP/ Reuters)

Mackenzie Philips’ struggle with addiction began when she was just 11-years-old when she first tried cocaine. The former child star’s drug use caused to her to be fired from “One Day at a Time.” In the years that followed, she was in and out of rehab and admitted to having a consensual sexual relationship with her father while she was married. In recent years, however, she has turned her life around. Currently Philips works as a drug counselor in Los Angeles.

2. Drew Barrymore


Actress Drew Barrymore (R) and Will Kopelman (L) attend the Museum of Modern Art's fourth annual Film Benefit in New York November 15, 2011. REUTERS/Kena Betancur (UNITED STATES - Tags: ENTERTAINMENT) - RTR2U2P7 (Reuters)

Drew Barrymore went to rehab when she was just 13 years old. Barrymore told Howard Stern that the counselors in rehab “saved her life.” The starlet went into an institution for the mentally ill. “(It was) no Hollywood rehab, 30-day, Malibu beachside bulls--t,” she said. “I swear to God it’s what I needed. I had nothing but freedom up until that point, partying it up, doing whatever I wanted…”

3. Corey Haim

Obit Haim

In this 1987 file publicity photo provided by NBC, actor Corey Haim, then star of the NBC comedy "Roomies," is shown. Haim, a 1980s teen heartthrob for his roles in "Lucas" and "The Lost Boys" whose career was blighted by drug abuse, died Wednesday, March 10, 2010. He was 38. (AP Photo/NBC) ** NO SALES ** (AP Photo/NBC)

Corey Haim struggled nearly his entire life to stay clean. At 16-years-old he smoked his first joint and then eventually did cocaine, which later led to crack. Haim went to rehab 15 times throughout his life. In an interview in 2007, Haim said he felt drugs ruined him to the point where he was not functional. In 2010, he died of an overdose at the age of 38.

4. Corey Feldman


Actor Corey Feldman arrives at the iHeartRadio Music Awards in Los Angeles, California May 1, 2014. REUTERS/Mario Anzuoni (UNITED STATES - Tags: ENTERTAINMENT) (iheartradio-ARRIVALS) - RTR3NGSJ (Reuters)

Corey Feldman has said he was introduced to heroin by a predator at 16-years-old. He told said in an interview he was “instantly addicted” to the drug. Feldman, however, has said he has since turned things around. He told People magazine in July that he was 25 years sober.

5. Aaron Carter


Singer Aaron Carter poses on the red carpet at the 52nd annual Grammy Awards in Los Angeles January 31, 2010. REUTERS/Mario Anzuoni (MUSIC-GRAMMYS/ARRIVALS) (UNITED STATES - Tags: ENTERTAINMENT) (Reuters)

Aaron Carter struggled with substance abuse from a very young age. The former pop star told E! News he first tried alcohol at 10-years-old. He’s also claimed that Michael Jackson gave him cocaine when Carter was 15. In 2011, at the age of 23, he checked himself into the Betty Ford Center to get help.

6. Cory Monteith


Cast member Cory Monteith poses at the Paley Center for Media's PlayFest 2011 event honoring the television series "Glee" at the Saban theatre in Los Angeles March 16, 2011. REUTERS/Mario Anzuoni (UNITED STATES - Tags: ENTERTAINMENT) - RTR2JZO3 (Reuters)

According to an in-depth piece on “Inside the Actor’s Studio,” “Glee” star Cory Monteith’s problems with drugs and alcohol began at 12-years-old. When he was 19-years-old his mom and friends staged an intervention, and he went to rehab. In March 2013, he checked himself into rehab again. That July, he died of an accidental overdose due to a fatal combination of alcohol and heroin. He was 31-years-old.