Zac Efron and 4 Other Celebrities That Went To Rehab For Secret Drug Addictions, Alcohol Abuse [PHOTOS]

News that former Disney star Zac Efron recently underwent a stint in rehab rocked Hollywood Tuesday. The 25-year-old actor, famous for singing and dancing in the popular tween film saga “High School Musical” and more recently starring in films such as "The Paper Boy" and “The Lucky One,” allegedly completed a rehab program roughly five months ago.

An insider close to the California native revealed to People magazine this week that Efron is doing well following his treatment for alleged cocaine abuse. “[He is] doing great. He’s taking care of himself, and it shows,” said a source. According to a report from TMZ, Efron was treated for a “serious cocaine addiction,” an issue which allegedly first became obvious on the set of his most recent film, “Neighbors.”

An eyewitness from the set of the comedy flick, due out in theaters next spring, claims the actor struggled with addiction during shooting and was frequently a no-show on set. "It was common knowledge he was struggling with cocaine,” said the source. Three other sources also made allegations that Efron was known to have dabbled in Ecstasy or "Molly."

While Efron’s alleged drug addiction issues and subsequent stay in rehab are shocking, he is hardly the only celebrity to battle substance abuse recently. Here are four others stars who also surprised the world by going to rehab this year:

LAMAR ODOM

NBA player Lamar Odom became a staple on the E! reality series “Keeping Up With the Kardashians” after marrying Khloe Kardashian in 2009. Despite his longstanding role in the hit TV show, Odom’s alleged battle with drug abuse only became public knowledge in August after he was arrested in California for suspected intoxication. Despite Odom’s claim that he is not a drug addict, the 33-year-old athlete entered a drug and alcohol rehabilitation center in September, only to leave one day later, according to a report from TMZ.

PHILIP SEYMOUR HOFFMAN

After 23 years of sobriety, Oscar award-winning actor Philip Seymour Hoffman relapsed into addiction earlier this year. The 46-year-old “Capote” star and upcoming lead in “The Hunger Games: Catching Fire” was reportedly treated at a detox center in May following reports that he had been abusing prescription pills and allegedly “snorting heroin,” according to a report from TMZ. Hoffman was reportedly treated for 10 days at an East Coast facility before checking out May 24.

FARRAH ABRAHAM

Former MTV “Teen Mom” star Farrah Abraham gave fans not one, but two shocks this year. The 22-year-old reality star first surprised the world by releasing a sex tape with porn star James Deen, only to land in rehab months later for reported alcohol abuse following a DUI arrest in Omaha, Neb. The single mom revealed to Radar Online in July that she voluntary attended a 10-day rehab program in Palm Beach Gardens, Fla., in an effort to “make better choices.” Unfortunately for Abraham, she was unceremoniously rejected from the treatment center just days later for disrupting other patients.

MIKE ‘THE SITUATION’ SORRENTINO

While drinking and partying was an everyday staple for stars of MTV’s former reality series “Jersey Shore,” one of its stars, Mike “The Situation” Sorrentino, faced addiction issues following his six-season run. Following rumors in March that he had entered a rehab facility, the 32-year-old confirmed the allegations via Facebook, saying, “I have voluntarily taken the steps to get control of a prescription medication problem I had due to exhaustion. I have spent the past several weeks getting treatment for this problem and recuperating from my work and appearance schedule. I appreciate my fans' support and love.” Earlier this week, the East Coast native revealed to the Los Angeles Times that he became addicted to drugs after he was prescribed painkillers following an injury he received while working on the hit ABC competition series, “Dancing With the Stars" in 2010.