According to the National Enquirer, 31-year-old Culkin is hooked on heroin and prescription painkiller oxycodone which has caused him to become so thin over the last year or so and even overdosed once.
"Macaulay Culkin is hooked on drugs and it's killing him!" a source told the tabloid. "He's been hooked for a year and a half, and his drug of choice is either heroin or oxycodone. Mac is surrounding himself with junkies and lowlifes. It's a real tragedy."
However, Culkin's legal team denied the accusations that he has a heroin and drug addiction along with axing the overdose rumor, Radar Online reported.
The report said that the former child star spends as much as $6,000 on drugs which he keeps in his New York City apartment, called a "drug lair."
The source said the root of the problem has been his breakup with former girlfriend Mila Kunis, causing the actor to experiment regularly with drugs.
"Macaulay Culkin is surely dying," another source told the Enquirer. "He's addicted to heroin, oxycodone, Percocet and Vicodin. I have witnessed his drug taking, which has escalated over the past year and a half to the point where he needs serious help."
The second source added that his physical condition is alarming, which has many worried about Culkin's life.
"His closest friends fear that he'll overdose or his heart will explode. If he doesn't get help and enter rehab now, he could be dead in six months," the source said. "It should have been a wake-up call, but it didn't seem to have any effect on him. Mac is still partying hard. I pray that he finds the courage and strength to clean up before it's too late."
Back in February, Culkin was seen in photos from "Entertainment Tonight" after cancelling an impromptu gig as a disc jockey in New York City looking more than just "skinny" or "thin," but terrifyingly gaunt. Witness who saw him said Culkin looked "super skinny" and "emaciated" wearing jeans and sneakers while holding Natalie Portman's the eight-month-old son, Aleph.
The photos prompted Culkin's rep to fire back, adding that the former "Home Alone" star is healthy.
"Macaulay Culkin is in perfectly good health," Culkin's rep told E! News. "For Entertainment Tonight, or any other media outlet, to speculate otherwise is reckless, irresponsible and destructive. We implore them to discontinue the rumor."
According to Entertainment Weekly, who posted the original photos of the gaunt actor, Macaulay Culkin was slated to star in a film in the UK, "Service Man," set for a 2013 release. However, the project is not credited on the actor's IMDb page.