A publicist for the former Home Alone star said the National Enquirer's claim that the actor had a $6000-a-month drug habit was "ridiculously fictitious" and "insulting".
The Enquirer alleged that Culkin was hooked on heroin and painkillers.
A source close to the actor told the gossip magazine: "Macaulay Culkin is hooked on drugs and it's killing him. 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."
The source also claimed that Culkin had nearly died from an overdose. "Mac suffered a near overdose, and needed help. Fortunately he didn't need to call 911 and the near-OD was kept quiet among his pals. But Mac got very sick."
Culkin's publicist, Michelle Bega, rubbished the report, saying it was "not only categorically without merit, but it is also impossibly and ridiculously fictitious".
"We beseech the responsible media to consider the source and its reputation and to please not perpetuate this destructive and insulting story by pursuing it any further," she said.