The filmmaker said that the film is an original story written by debutante director Shakun Batra and is not inspired by the Cameron Diaz-Ashton Kutcher starrer hit rom-com.
"The movie is not an adaptation. It is an original story written by the writer of the film and Shakun is the director of the film with Imraan and Kareena in it. It is not an adaptation of What happens in Vegas," Johar told PTI.
The 38-year-old director also dismissed stories that he asked Kareena to regain her size zero figure for the venture, and even have a haircut for the role.
"I have not had any conversation about this with Kareena. This is just taken off and acquired it's own life. She will look the way she does -- lovely and beautiful like she is," said Johar, who was in the city to attend the launch of apparel store The Collective.
His latest production We are Family, directed by Siddharth Malhotra, an official adaptation of Hollywood flick Stepmom has received mixed response at the box office.
"I don't think We Are Family is a rip off. People don't even remember the original Stepmom at all. It is a true adaptation. There are tracks and scenes in the movie that don't even exist in the original. We haven't copied anything. We gave a price that means we own content which means we can replicate it in our way," he said.
"We are happy with it's reception and are excited that we have managed to give it an Indian touch and yet not make it regretful in any way."
Apart from the movie, Elvis Presley's classic song Jail House Rock called as Dil khol ke let's rock have also been composed with Hindi lyrics on the tunes of the original. It seems that the composers wanted to repeat the success of their previous song song Pretty Woman from Kal Ho Naa Ho, but somehow it did not work.
"Pretty Women rocked, Let's rock may not have... But, you take your chance creatively," Johar said. Talking on Hollywood adaptations in Bollywood Johar said, "Adaptation is a director's prerogative. But it should not be an order of the day or a norm or a herd mentality. If it happens naturally and organically then why not."
Kareena: My weight has been a national issue
Spotted: Karan Johar in London
Picture perfect, Kareena Kapoor
'Property prices in Pune have increased by 12.5%'
First look: Kajol, Kareena in Stepmom remake