The 31-year-old was allegedly present at the pair's starlight ceremony, days after sensational reports emerged from the National Enquirer that the Home Alone star was a drug addict and 'hooked on hillbilly heroin.'
The two exchanged vows in a Jewish ceremony under a chuppah at 8pm.
According to Us Weekly, Natalie and Culkin have been 'friends for years.'
Natalie also co-starred in Black Swan with his former girlfriend Mila Kunis.
A spokeswoman for the 31-year-old actor branded the claims published in the National Enquirer as 'ridiculously fictitious' and 'insulting'.
The American tabloid reported that Culkin regularly shoots up heroin and the highly addictive painkiller oxycodone - dubbed hillbilly heroin.
The article went on to say the former child star turned his Manhattan apartment into a drug den where he gets high either by himself or with friends.
Ms Bega added that the story was 'destructive and insulting,' to her client.
The Enquirer claims Culkin's drug use intensified 18 months ago - around the time he split from long-term girlfriend Kunis, who is now dating Ashton Kutcher.
A source told the publication: '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 - described by the Enquirer as a 'close friend' - also claimed Culkin has had a close brush with death in the past year and almost overdosed.
'Mac suffered a near overdose, and needed help,' the insider said.
'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 half sister Jennifer Adamson died of a drug overdose in 2000.
Following Culkin's denial, the National Enquirer issued a statement to say that they were firmly standing by their story. The Enquirer's statement also refers to Rosello.
In the article, the magazine alleged Culkin and Rosello used to do drugs together which is reiterated in the statement.
It went on: 'We believe that the former child star should be doing everything he can to get the treatment he so desperately needs – and which could have saved the life of his friend Elijah Rosello.
'Her family confirmed to The ENQUIRER that she did drugs with Macaulay before her drug-related death in March.'
The US tabloid posted a statement on its website, urging the former Home Alone star to seek urgent professional help - and challenged him to take a blood test.
'Should Macaulay’s representatives continue to deny The ENQUIRER’s accurate and detailed report, we are ready to offer him the opportunity to take a blood test administered by an independent medical lab,' challenged the magazine.
It adds: 'Our advice to Macaulay is to seek professional help to avoid the same tragic fate of other beloved celebrities, including Whitney Houston who died earlier this year.'
In February, pictures of of Culkin looking emaciated and shockingly thin made headlines.
At the time his representatives strenuously denied the actor was addicted to prescription drugs or heroin amid reports the 5-foot-7 star's weight had dropped to 104lbs.
Macaulay is best know for his roles as cheeky Kevin McCallister in the 1990 film Home Alone and the 1992 sequel, Home Alone: Lost In New York.
He also starred in the likes of Uncle Buck, My Girl and Richie Rich.
But his adult career has failed to match the blockbuster success of his childhood days.
In 2003 he played a drug-addled club hopper alongside Seth Green in Party Monster, while his last film role was in 2007 in the Indie flick Sex And Breakfast.
These days he earns a living DJ-ing at clubs around New York.
Read more: http://www.dailymail.co.uk/tvshowbiz/article-2184244/Macaulay-Culkin-attends-Natalie-Portmans-wedding-Big-Sur-reports-hooked-heroin.html#ixzz22tMml8ip
