SINGAPORE - The highly anticipated drama Pop Aye from Singapore film-maker Kirsten Tan has been given an M18 rating by the Infocomm Media Development Authority (IMDA).

This means that only those aged 18 and older will be able to view the film.

Speaking to the media at a conference on Tuesday (April 4), executive producer Anthony Chen says the stringent rating took him by surprise.

"I didn't think the film would get an M18, to be honest. I thought it would be NC16. I've seen full frontal nudity with NC16. But it's a good film and I want audiences to see it in the way it should be seen," he says, adding that the version shown here when it opens on April 13 will be same as the one shown internationally.

IMDA's film classification website describes the Thai-language film - about a middle-aged man who embarks on a whimsical cross-country journey with an elephant he rescues - as having sexual scenes, including one of oral sex.

It also "shows a couple engaging in sex in a dimly lit room with the focus on their upper bodies, with sexual motions visible. Such depictions are contained under a M18 rating."

The film also contains "female upper body nudity" and "infrequent use of the word 'f***' in the film's subtitles," according to the IMDA.

Chen, looking on the bright side, adds that once it is known that the drama contains raunch, it will be good for the film's marketing.

"Maybe, now that it's M18, it will attract more people," he says.

Chen, 32, who directed Ilo Ilo (2013), the family drama that won the Camera d'Or at the Cannes Film Festival, and Tan, 36, also spoke about the screenplay's long gestation over two years. Ms Tan's drafts were pored over by Chen, who made suggestions.

Chen's label, Giraffe Pictures, is producing the movie, Ms Tan's feature debut.

She based the character of Thana, the man going through a mid-life crisis in the film, on men she had met in her life, including her father.

"People like Thana are all around us," she says.

Chen says: "Sometimes I would send her 20 pages of notes."

His goal was to make sure that Ms Tan retained her own distinct voice, and to enforce the rule that whenever a character did anything, it was done with a clear motive. He hopes that this rigorous script development process, which can take years and is the norm in the West, takes root in Singapore.

Lead actor Thaneth Warakulnokroh, 58, plays Thana, the man who reunites with the elephant who had been his best friend as a boy.

He had acted on television, films and on stage when he was younger, but dropped acting to become a rock musician. He eventually stopped acting to focus on a career in music production 30 years ago.

Coming back to acting in Ms Tan's film was easy because he identified with the issues Thana faced, he says.

Neither was there any stress in knowing that, as the lead, he would be in almost every scene.

"It makes me proud. Most actors want to be in a film like that, where they carry the story on their shoulders."